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Abstract

Background:

Considering the lengthy recovery and high recurrence risk after a hamstring injury, effective rehabilitation and accurate prognosis are fundamental to timely and safe return to play (RTP) for athletes.

Purpose:

To analyze methods of rehabilitation for acute proximal and muscular hamstring injuries and summarize prognostic factors associated with RTP.

Study Design:

Systematic review; Level of evidence, 4.

Methods:

In August 2020, MEDLINE, CINAHL, Cochrane Central Register of Controlled Trials, and SPORTDiscus were queried for studies examining management and factors affecting RTP after acute hamstring injury. Included were randomized controlled trials, cohort studies, case-control studies, and case series appraising treatment effects on RTP, reinjury rate, strength, flexibility, hamstrings-to-quadriceps ratio, or functional assessment, as well as studies associating clinical and magnetic resonance imaging factors with RTP. Risk of bias was assessed using the Cochrane Risk-of-Bias Tool for Randomized Trials or the Methodological Index for Non-Randomized Studies (MINORS).

Results:

Of 1289 identified articles, 75 were included. The comparative and noncomparative studies earned MINORS scores of 18.8 ± 1.3 and 11.4 ± 3.4, respectively, and 12 of the 17 randomized controlled trials exhibited low risk of bias. Collectively, studies of muscular injury included younger patients and a greater proportion of male athletes compared with studies of proximal injury. Surgery for proximal hamstring ruptures achieved superior outcomes to nonoperative treatment, whereas physiotherapy incorporating eccentric training, progressive agility, and trunk stabilization restored function and hastened RTP after muscular injuries. Platelet-rich plasma injection for muscular injury yielded inconsistent results. The following initial clinical findings were associated with delayed RTP: greater passive knee extension of the uninjured leg, greater knee extension peak torque angle, biceps femoris injury, greater pain at injury and initial examination, “popping” sound, bruising, and pain on resisted knee flexion. Imaging factors associated with delayed RTP included magnetic resonance imaging-positive injury, longer lesion relative to patient height, greater muscle/tendon involvement, complete central tendon or myotendinous junction rupture, and greater number of muscles injured.

Conclusion:

Surgery enabled earlier RTP and improved strength and flexibility for proximal hamstring injuries, while muscular injuries were effectively managed nonoperatively. Rehabilitation and athlete expectations may be managed by considering several suitable prognostic factors derived from initial clinical and imaging examination.

Keywords

hamstring injury imaging rehabilitation return to play

Hamstring injury is one of the most common injuries among athletes.³¹ Athletes involved in activities requiring high-speed running^6,10 or stretching to extreme muscle lengths^7,8 are particularly subject to hamstring injury, which is classified according to location within the muscle complex, specific muscle(s) affected, severity, and chronicity. Because of the complex anatomic and biomechanical properties necessary to facilitate movement at both the hip and the knee, however, uniform assessment of hamstring injury epidemiology is challenging.²² Determining whether the injury affects the proximal origin or muscle belly is an important first step to elucidating injury epidemiology, understanding clinical presentation, and identifying potential complications. Proximal hamstring injuries occur predominantly in middle-aged patients and are often more severe,⁴³ usually associated with prolonged convalescence and carrying greater risk for complications such as postoperative weakness and sciatic nerve injury.^13,81 Conversely, muscular injuries occur more commonly in younger male athletes with risk factors such as strength or flexibility deficits, and although initially milder than proximal injuries, there exists substantial risk for recurrent injury of greater severity.^32,67

Consideration of injury location is also important when determining clinical management. Although approach to rehabilitation is tailored according to injury location, severity, and patient goals of therapy, management generally includes physiotherapy^∥ with possible concomitant surgical intervention^¶ or injections of platelet-rich plasma (PRP).^＃ Despite extensive research investigating methods of rehabilitation and advances in therapeutic techniques designed to return athletes to competition quickly while minimizing reinjury risk,^61,74 acute hamstring injury continues to account for significant absence from sports, and little consensus has been reached regarding optimal management strategies. Accurate prediction of time to return to play (RTP) is necessary to guide activity progression and manage patient expectations for recovery. Although clinicians often rely on clinical and structural factors gleaned from initial examination and magnetic resonance imaging (MRI) scans to inform their prognosis, whether these adequately correlate with recovery time remains a topic of debate.

The purpose of this study was to systematically review the literature concerning evidence-based management of acute proximal and muscular hamstring injuries in athletes and to report the baseline clinical and MRI factors associated with RTP.

Methods

Research Framework

The design and reporting of this systematic review are compliant with the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines.⁶⁰

Eligibility Criteria

English-language articles examining management and factors affecting RTP after acute hamstring injury were considered for eligibility, and those meeting each of the following criteria were included: (1) the article employed a randomized controlled trial (RCT), cohort, case-control, or case series design; (2) patients had sustained acute proximal or muscular hamstring injury, defined as <6 weeks between injury and initial evaluation; (3) the authors investigated the effects of a well-described intervention on hamstring rehabilitation or associated baseline clinical or MRI assessment findings with RTP; and (4) outcome measures included time to RTP, reinjury rate, hamstring strength, hamstring range of motion (ROM), hamstrings-to-quadriceps (H:Q) ratio, or results of standardized functional assessment. Studies limited to only chronic tendinopathy or only recurrent hamstring injuries were excluded.

Information Sources and Search

Searches of MEDLINE (1966 to present), CINAHL (1981 to present), Cochrane Central Register of Controlled Trials (1996 to present), and SPORTDiscus (1949 to present) were conducted in August 2020. To identify articles pertinent to acute hamstring injury management and prognosis, a comprehensive search strategy was developed using applicable Medical Subject Headings terms and keywords (see Appendix Table A1). Subsequent manual inspection of included article reference lists ascertained any additional relevant articles not found via the computerized search.

Study Selection

Two reviewers (S.S.R. and M.P.K.)independently screened all articles on the basis of title and abstract using a specialized systematic review software (Covidence systematic review software; Veritas Health Innovation). Potentially eligible articles underwent full-text review prior to final determination of study inclusion. Any disagreements between reviewers were resolved via discussion.

Data Collection

Based on the Cochrane Handbook for Systematic Reviews of Interventions recommendations for data extraction,²⁸ a custom data extraction form was developed to collect information on study design; methods; population; intervention(s); and outcome measures, including time to RTP, reinjury rate, hamstring strength, hamstring ROM, H:Q ratio, and/or standardized functional assessment. All data were extracted by a single reviewer (S.S.R.) and verified by a second reviewer (M.P.K.).

Risk-of-Bias and Quality Assessment

A risk-of-bias assessment was performed for all included studies. RCTs were assessed using the Revised Cochrane Risk-of-Bias Tool for Randomized Trials, which appraises studies based on patient randomization, assignment to intervention, availability of outcome data, outcome measurement, and selection of reported results.⁸⁰ Overall risk of bias for each RCT was judged as “low,” “some concerns,” or “high.” Nonrandomized studies were assessed using the Methodological Index for Non-Randomized Studies (MINORS) tool.⁷⁹ The MINORS tool represents a 12-item assessment of methodological value, with 8 criteria indicated for noncomparative studies and an additional 4 criteria indicated for comparative studies. Each criterion was scored from 0 to 2, with higher overall scores indicating higher quality of evidence.

Statistical Analysis

Patient characteristics were quantified using descriptive statistics, calculated as weighted means and standard deviations across included studies. We used t tests to identify any differences in characteristics between patients with acute proximal and muscular hamstring injuries. A P value < .05 was used to determine statistical significance. Stata (Version 13.1; StataCorp) software was used for all statistical analyses.

Results

Study Selection

The database search retrieved 1704 articles, with an additional 22 identified via manual search as potentially relevant. After removing duplicates, 1289 articles were screened on the basis of title and abstract. A total of 126 articles were retained for full-text review, of which 51 were excluded for failure to satisfy the inclusion criteria, and 75 were included (Figure 1).

Figure 1.

Study flowchart.

Study Characteristics

A total 45 of the included studies pertained to injury management,** 25 defined factors associated with RTP,^†† and 5 integrated both.^1,9,10,45,76 Studies investigated 3 to 360 male and female athletes engaged in various sports of all competitive levels with a mean age of 14 to 58 years. Of the studies pertaining to injury management, 22^‡‡ concerned injuries to the proximal origin, and 28^§§ were specific to muscular injuries. A variety of techniques and programs were assessed according to recovery time, reinjury risk, and degree of functional improvement, including surgical and nonsurgical treatment,^∥∥ PRP injection,^¶¶ and physiotherapeutic interventions.^## There was a lack of uniformity across studies regarding diagnostic methods, criteria for RTP, and assessment of outcomes. Prognostic studies determined whether baseline findings were correlated with time to RTP by conducting clinical and/or MRI assessment shortly after injury.

Of note, study samples were duplicated in a few articles.^{5
–7,39,40,44,83,85} Specifically, injuries to the 18 sprinters and 15 dancers described in Askling et al⁵ were also investigated separately in 2 other studies by the same authors.^6,7 Hamilton et al,⁴⁰ Jacobsen et al,⁴⁴ van der Made et al,⁸³ and Wangensteen et al⁸⁵ additionally shared considerable overlap in patient populations due to their use of pooled data from a prior RCT.³⁹

Risk-of-Bias Assessment

Seventeen RCTs were included, of which 12 were determined to present low risk of bias,^a and 5 were judged to raise some concerns.^{9,10,46,49,70} Nonrandomized studies comprised 11 comparative^b and 47 noncomparative^c designs with average scores of 18.8 ± 1.3 and 11.4 ± 3.4 on MINORS assessment, respectively.

Synthesis of Results

Patient Characteristics

Acute hamstring injuries were classified according to location within the muscle complex. Collectively, 775 patients with proximal hamstring injury and 1057 patients with muscular hamstring injury were assessed by the included studies. Studies investigating methods of proximal injury management generally included younger patients and a greater proportion of male patients compared with studies of proximal hamstring injury rehabilitation (Table 1).

TABLE 1
Comparison of Patient Characteristics Between Studies of Proximal Versus Muscular Hamstring Injury ^a

Studies of Proximal Hamstring Injury Management Studies of Muscular Hamstring Injury Management

No. of patients 775 1057

Patient age, y, mean ± SD 42.4 ± 10.5 26.2 ± 6.5

Patient sex, % male 57.2 87.6

^a Bold values were statistically significantly different between groups (P < .05).

Management

Management of hamstring injury was also dependent upon localization to the proximal origin or muscle belly. Time to RTP and reinjury rate at final follow-up are listed according to intervention in Tables 2 to 4. Because of extensive variation in the methods of measuring and reporting hamstring strength, ROM, H:Q ratio, and functional assessment, individual study results for these outcomes are discussed in the text only and not presented in the tables.

TABLE 2
Summary of Studies on Management of Acute Injuries to the Proximal Hamstring ^a

Additional Outcomes

Lead Author (Year) Risk of Bias ^b Injury Type Intervention N Mean ± SD Time to RTP, d Reinjury Rate, % Mean Follow-up, mo Hamstring Strength Hamstring ROM H:Q Ratio Functional Assessment

Arner (2019)⁴ 9 (16) Partial proximal hamstring avulsion Surgical 64 333 (range, 150-1440) — 78 X

Ayuob (2020)¹¹ 12 (16) Complete proximal semimembranosus rupture Surgical 20 83.3 ± 39.9 0.0 35 X X X

Ayuob (2020)¹² 12 (16) Partial/complete tear of proximal MTJ of long head of biceps Surgical 64 93.8 ± 35.7 — 24 X X X

Barnett (2015)¹³ 10 (16) Partial/complete proximal hamstring avulsion Surgical 38 — — 54 X

Best (2019)¹⁵ 9 (16) Complete proximal hamstring avulsion Surgical 49 — — 28 X

Biedert (2015)¹⁷ 9 (16) Avulsion fracture of ischial tuberosity Surgical 3 — — 24 X

Birmingham (2011)¹⁸ 11 (16) Complete proximal hamstring avulsion Surgical 23 294 (range, 90-1080) — 43 X X

Blakeney (2017)¹⁹ 15 (16) Partial/complete proximal hamstring avulsion Surgical 96 — — 34 X

Bowman (2013)²⁰ 10 (16) Partial proximal hamstring avulsion Surgical 17 — — 32 X

Chahal (2012)²³ 9 (16) Complete proximal hamstring avulsion Surgical 13 — — 24 X X

Hofmann (2014)⁴² 9 (16) Complete proximal hamstring avulsion Nonoperative 17 — — 31 X X

Klingele (2002)⁴⁷ 10 (16) Complete proximal hamstring avulsion Surgical 11 180 (range, 90-300) — 34 X

Konan (2010)⁴⁸ 12 (16) Complete proximal hamstring avulsion Surgical 10 175 (range, 126-455) — 12 X X

Lefevre (2013)⁵¹ 18 (24) Partial/complete proximal hamstring avulsion Surgical 34 171 ± 48 — 27 X X X

Léger-St-Jean (2019)⁵² 12 (16) Complete proximal hamstring avulsion Surgical 22 120 (IQR, 60-240) — 6 X

Lempainen (2006)⁵⁴ 10 (16) Partial proximal hamstring avulsion Surgical 48 150 (range, 30-360) — 36

Piposar (2017)⁶² 18 (24) Partial/complete proximal hamstring avulsion (1) Surgical(2) Nonoperative 1510 — — 3035 X X

Sandmann (2016)⁶⁸ 11 (16) Complete proximal hamstring avulsion Surgical 16 180 (range, 120-270) — 56 X X X

Shambaugh (2017)⁷² 17 (24) Complete proximal hamstring avulsion (1) Surgical(2) Nonoperative 1411 — — 4330 X X

Skaara (2013)⁷⁷ 9 (16) Partial proximal hamstring avulsion Surgical 31 — — 30 X X X

Subbu (2014)⁸¹ 12 (16) Complete proximal hamstring avulsion Surgical 78 112 (range, 84-224) 0.0 24

Willinger (2020)⁸⁷ 11 (16) Partial/complete proximal hamstring avulsion Surgical 71 — — 56 X

^a Dashes indicate data not reported. H:Q, hamstrings-to-quadriceps ratio; IQR, interquartile range; MTJ, myotendinous junction; ROM, range of motion; RTP, return to play; X, outcome(s) reported.

^b Reported as Methodological Index for Non-Randomized Studies score (maximum score).

TABLE 3
Summary of Studies Managing Acute Muscular Hamstring Injury Using PRP or Autologous Conditioned Serum ^a

Additional Outcomes

Lead Author (Year) Risk of Bias ^b Injury Type Intervention N Mean ± SD Time to RTP, d Reinjury Rate, % Mean Follow-up, mo Hamstring Strength Hamstring ROM

A Hamid (2014)¹ Low Grade 1 (1) PRP (1 × 3-mL direct injection 5 d postinjury(2) No injection 1414 26.7 ± 7.0 ^c 42.5 ± 20.6 ^c — — X

Bezuglov (2019)¹⁶ Low BAMIC 2a/2b (1) PRP (1 × 8-mL direct injection <48 h postinjury)(2) Saline (1 × 8-mL direct injection <48 h postinjury) 2020 11.4 ± 1.2 ^c 21.3 ± 2.7 ^c 0.00.0 6

Bradley (2020)²¹ 18 (24) Cohen grade 2 (1) PRP (1-3 × 2- to 5-mL direct injections 1 wk apart)(2) No injection 3039 22.5 ± 20.125.7 ± 20.6 3.32.6 —

Gaballah (2018)³³ Low Grade 2 (1) PRP (1 × 3-mL direct injection, 5-7 d postinjury)(2) No injection 89 Maximum, 27 ^c Maximum, 43 ^c — — X

Guillodo (2015)³⁷ 19 (24) Grade 3 (1) PRP (1 × 3-mL direct injection <8 d postinjury)(2) No injection 1519 50.9 ± 10.752.8 ± 15.7 — —

Hamilton (2015)³⁹ Low Grade 1-2 (1) PRP (3 × 1-mL injections 1 cm apart, <5 d postinjury)(2) PPP (3 × 1-mL injections 1 cm apart, <5 d postinjury)(3) No injection 303030 21 (95% CI, 18-24) ^c 27 (95% CI, 21-33) ^c 25 (95% CI, 22-29) 7.710.710.3 6 X

Lee (2020)⁵⁰ 12 (16) Grade 1-3 PRP (single injection) 8 49 (range, 10-112) — —

Rettig (2013)⁶⁵ 18 (24) Grade 1-2 (1) PRP (1 × 9-mL direct injection <48 h postinjury)(2) No injection 55 20 (range, 16-30)17 (range, 8-81) — —

Reurink (2015)⁶⁶ Low Grade 1-2 (1) PRP (3 × 1-mL injections 1 cm apart at 5 and 10 d postinjury)(2) Saline (3 × 1-mL injections 1 cm apart at 5 and 10 d postinjury) 4139 42 (IQR, 30-58)42 (IQR, 37-56) 27.029.7 12 X X

Wright-Carpenter (2004)⁸⁸ 19 (24) Grade 2 (1) Autologous conditioned serum (5 × 1-mL injections over area of injury every 2nd day [mean, 5.4 injections])(2) Actovegin/Traumeel therapy (5 × 1-mL injections over area of injury every second day [mean, 8.3 injections]) 65 16.3 ± 3.1 ^c 21.8 ± 4.8 ^c — —

Zanon (2016)⁸⁹ 12 (16) Grade 2 PRP (2-3 × 3-mL injections at 72 h and 7 d postinjury) 25 35.1 ± 18.9 12.0 37

^a Dashes indicate data not reported. BAMIC, British Athletics Muscle Injury Classification; IQR, interquartile range; PPP, platelet-poor plasma; PRP, platelet-rich plasma; ROM, range of motion; RTP, return to play; X, outcome(s) reported.

^b Reported as Methodological Index for Non-Randomized Studies score (maximum score) for nonrandomized studies or Cochrane Risk-of-Bias Tool for Randomized Trials.

^c Significant difference between interventions (P < .05).

TABLE 4
Summary of Studies Managing Acute Injuries to Hamstring Muscle With Physiotherapy ^a

Additional Outcomes

Lead Author (Year) Risk of Bias ^b Injury Type Intervention(s) N Mean ± SD Time to RTP, d Reinjury Rate, % Mean Follow-up, d Hamstring Strength Hamstring ROM H:Q Ratio Functional Assessment

Albertin (2020)³ 10 (16) Grade 2 Primal Reflex Release Technique 6 — — — X X

Askling (2013)¹⁰ Some concerns Sprinting or stretching (1) L-protocol(2) C-protocol 3738 28 ± 15 ^c 51 ± 21 ^c 0.02.6 12

Askling (2014)⁹ Some concerns Sprinting or stretching (1) L-protocol(2) C-protocol 2828 49 ± 26 ^c 86 ± 34 ^c 0.07.1 12

Bayer (2018)¹⁴ Low Munich type 3-4 (1) Early rehab(2) Delayed rehab 2022 62.5 (IQR, 48.8-77.8) ^d 83.0 (IQR, 64.5-97.3) ^d 9.10.0 12 X X

Hickey (2020)⁴¹ Low Grade 1-2 (1) Pain-threshold rehab(2) Pain-free rehab 2122 17 (95% CI, 11-24)15 (95% CI, 13-17) 9.59.1 6 X

Kilcoyne (2011)⁴⁵ 10 (16) Grade 1-2 Early, progressive rehab 48 11.9 (range, 5-23) 6.3 6

Kim (2018)⁴⁶ Some concerns Grade 2 Stretching and ROM-based rehab 13 — — 2 X X

Kornberg (1989)⁴⁹ Some concerns Grade 1 (1) Slump stretching(2) Standard rehab 1216 1 absent >1 game ^c 16 absent >1 game ^c — —

Malliaropoulos (2004)⁵⁶ Low Grade 2 (1) 1× daily stretching(2) 4× daily stretching 4040 15.1 ± 0.8 ^c 13.3 ± 0.7 ^c — — X

Medeiros (2020)⁵⁷ Low Grade 1-2 (1) LLLT protocol(2) Standard rehab 1111 23.1 ± 9.123.8 ± 12.6 0.00.0 6 X X

Mendiguchia (2017)⁵⁸ Low Grade 1 (1) Rehab algorithm(2) Rehab protocol 2424 25.5 ± 7.823.2 ± 11.7 4.2 ^d 25.0 ^d 6

Sefiddhashti (2018)⁷⁰ Some concerns Grade 1-2 (1) Cryotherapy with stretching(2) Cryotherapy alone 1819 — — 0.25 X X

Sherry (2004)⁷³ Low Grade 1-2 (1) STST protocol(2) PATS protocol 1113 37.4 ± 27.622.2 ± 8.3 70.0 ^c 7.7 ^c 12

Silder (2013)⁷⁶ Low Grade 1-2 (1) PATS protocol(2) PRES protocol 1312 28.8 ± 11.425.2 ± 6.3 16.723.1 12 X

Tyler (2017)⁸² 11 (16) Grade 1-3 Eccentric strength protocol 50 77 ± 70 8.0 24 X

^a Dashes indicate data not reported. C-protocol, conventional protocol; H:Q, hamstrings-to-quadriceps ratio; IQR, interquartile range; L-protocol, lengthening protocol; LLLT, low-level laser therapy; PATS, progressive agility and trunk stabilization; PRES, progressive running and eccentric strengthening; rehab, rehabilitation; ROM, range of motion; RTP, return to play; STST, stretching and strengthening; X, outcome(s) reported.

^b Reported as Methodological Index for Non-Randomized Studies score (maximum score) for nonrandomized studies or Cochrane Risk-of-Bias Tool for Randomized Trials.

^c Significant difference between interventions (P < .001).

^d Significant difference between interventions (P < .05).

Proximal Injuries

To determine optimal treatment for acute proximal hamstring injuries, 22 studies investigated the efficacy of surgical and nonsurgical intervention^‡‡ (Table 2). When supplemented with postoperative rehabilitation, surgical repair for partial avulsion was associated with a high rate of RTP^13,51,87 and low levels of pain and functional limitation.^4,20,54,77 Piposar et al⁶² found no differences in objective outcomes between operative and nonoperative management, although subjective results were superior after surgery. Satisfactory operative results were also observed in the context of complete avulsion, regardless of tendon retraction^19,48,52,81 or ischial tuberosity fracture.¹⁷ Mean hamstring strength recovered to 78.0% to 94.6% within 12 months of surgery, and the rate of RTP surpassed 75%,^11,18,47,81 although up to 45% of patients reported decreased level of activity.^23,87 Two studies measuring hamstring ROM demonstrated >90% recovery within 12 months of surgical repair.^11,12 Functional outcomes did not differ by sex in any study except that by Chahal et al,²³ in which all 4 patients experiencing poor outcomes were female. Comparatively, nonoperative management of complete proximal avulsion resulted in noticeable strength deficits and lower functional scores.⁴²

Muscular Injuries

Management of acute muscular hamstring injury was the focus of 28 studies. Eleven studies evaluated the efficacy of autologous PRP^d or autologous conditioned serum⁸⁸ injection using various injection volumes, locations, and frequencies (Table 3). Although 3 studies found patients receiving PRP achieved earlier RTP than controls by 10 to 15 days,^1,16,33 5 studies showed no such effect.^{21,37,39,65,66} Despite finding no relationships between PRP injection and days or practices missed because of hamstring injury in National Football League athletes, Bradley et al²¹ reported PRP injection to be associated with fewer games missed. Zanon et al⁸⁹ noted a decreased reinjury rate in patients receiving PRP in the short term; however, the long-term rate was not different from that of controls. None observed strength differences associated with PRP injection^1,39,66 except Gaballah et al,³³ who demonstrated a transient increase in strength 4 weeks after injection relative to controls that dissipated by week 8. Only Reurink et al⁶⁶ measured hamstring ROM and elucidated no effect of PRP injection on straight-leg raise or active knee extension ROM. None of the included studies concerning PRP or autologous conditioned serum injection reported the H:Q ratio or standardized functional assessment.

Physiotherapeutic programs for acute hamstring muscular injuries were assessed in 15 studies^e (Table 4). Eccentric training enabled faster RTP for elite soccer¹⁰ and track and field⁹ athletes compared with conventional training regardless of whether the injury was of sprinting or stretching type. Reinjury rate did not differ between eccentric and conventional rehabilitation protocols.^9,10 However, athletes fully compliant with an eccentric training program experienced fewer reinjuries and reduced strength deficits compared with noncompliant patients.⁸² Reinjury risk was further reduced via an individualized rehabilitation algorithm designed to address risk factors, although this approach resulted in possibly slower RTP.⁵⁸

Kim et al⁴⁶ found stretching and ROM exercises were effective in restoring passive ROM and reducing pain in athletes with grade 2 injury, but active ROM and strength were not improved.⁴⁶ Active ROM was increased by increasing the frequency of stretching from 1 to 4 daily sessions, however, as patients were quicker to normalize flexibility between injured and uninjured limbs and RTP.⁵⁶ Stretching after icing (“cryostretching”) yielded greater increases in active knee extension and lower extremity functional scale scores compared with icing alone.⁷⁰ A stretching and strengthening (STST) intervention was compared with progressive agility and trunk stabilization (PATS) by Sherry and Best,⁷³ who reported similar time to RTP between groups but a significantly greater reinjury rate in the 12 months after STST. Silder et al⁷⁶ compared a progressive running and eccentric strengthening program with PATS and found no benefit in RTP, reinjury risk, strength, or ROM. Notably, all 25 athletes in this study displayed residual injury markers on MRI scans at RTP, and half of those who experienced reinjury did so within 2 weeks.

Two studies demonstrated the benefit of early intervention.^45,14 After 24 hours of immobilization, a progressive rehabilitation program developed by Kilcoyne et al⁴⁵ returned patients with grade 1 to 2 injury to activity in an average of <2 weeks with a 6-month reinjury rate of 6.3%. Athletes who began physiotherapy 2 days after grade 3 to 4 injury achieved faster RTP than athletes beginning at 9 days, with no difference in reinjury rate within 1 year.¹⁴ Peak hamstring strength was increased in the early group 13 weeks after injury, but this difference disappeared by 26 weeks. Both early and late groups exhibited decreased H:Q ratios compared with the uninjured leg. Hickey et al⁴¹ determined that pain threshold—based rehabilitation failed to accelerate RTP or influence reinjury rate relative to pain-free therapy. However, isometric hamstring strength was 15% greater after 2 months of training in the pain-threshold group. The Primal Reflex Release Technique, a method of downregulating the autonomic nervous system to reset reflexes via reciprocal inhibition, was shown to significantly increase active and passive ROM as well as functional scores.³ A neurologically based approach was also examined by Kornberg and Lew,⁴⁹ who reported that slump stretching resulted in fewer games missed after grade 2 injury in Australian Rules football players. Last, an RCT by Medeiros et al⁵⁷ investigating low-level laser therapy revealed no effect in any reported outcome measure.

Surgical intervention for muscular injury was examined in 2 studies. Lempainen et al⁵³ (MINORS score, 10/16) assessed outcomes of surgical repair for muscular injury with concomitant complete rupture of the central hamstring tendon, reporting RTP within 4 months and no reinjuries by 1 year for the 2 patients with nonrecurrent injury included in the study. In addition, Cooper and Conway²⁶ (MINORS score, 18/24) compared surgical and nonoperative treatments for complete distal semitendinosus rupture and found no difference in time to RTP. However, 42% of patients treated nonoperatively did not achieve acceptable results and required subsequent surgical intervention.

Prognostic Factors

Characteristics and findings of studies correlating baseline clinical and/or MRI findings with time to RTP are summarized in Tables 5 and 6.

TABLE 5
Summary of Studies Assessing Prognostic Value of Baseline Assessment ^a

Assessment

Lead Author (Year) Risk of Bias ^b N Clinical MRI

A Hamid (2014)¹ Low 28 X

A Hamid (2013)² 10 (16) 360 X

Askling (2006)⁵ 12 (16) 33 X

Askling (2007)⁶ 14 (16) 15 X X

Askling (2007)⁷ 14 (16) 18 X X

Askling (2008)⁸ 11 (16) 30 X X

Askling (2014)⁹ Some concerns 56 X X

Askling (2013)¹⁰ Some concerns 75 X X

Cohen (2011)²⁴ 14 (16) 38 X

Comin (2013)²⁵ 20 (24) 62 X

Crema (2018)²⁷ 11 (16) 22 X

Ekstrand (2012)²⁹ 12 (16) 207 X

Ekstrand (2016)³⁰ 12 (16) 255 X

Gibbs (2004)³³ 12 (16) 31 X

Guillodo (2014)³⁶ 12 (16) 128 X

Hallen (2014)³⁷ 13 (16) 386 X

Hamilton (2018)⁴⁰ 13 (16) 110 X

Jacobsen (2016)⁴⁴ 14 (16) 90 X X

Kilcoyne (2011)⁴⁵ 10 (16) 48 X

Malliaropoulos (2010)⁵⁵ 21 (24) 165 X

Moen (2014)⁵⁹ 13 (16) 74 X X

Pollock (2016)⁶³ 11 (16) 44 X

Pomeranz (1993)⁶⁴ 10 (16) 14 X

Schneider-Kolsky (2006)⁶⁹ 21 (24) 58 X X

Silder (2013)⁷⁶ Low 25 X

Slavotinek (2002)⁷⁵ 12 (16) 30 X

van der Made (2018)⁸⁰ 14 (16) 70 X

Verrall (2003)⁸¹ 12 (16) 83 X X

Wangensteen (2015)⁸² 11 (16) 180 X X

Warren (2010)⁸³ 13 (16) 59 X

^a MRI, magnetic resonance imaging; X, outcome(s) reported.

^b Reported as Methodological Index for Non-Randomized Studies score (maximum score) for nonrandomized studies or Cochrane Risk-of-Bias Tool for Randomized Trials.

TABLE 6
Baseline Assessment Findings and Prognostic Relationships With RTP Times ^a

Clinical Factors MRI Factors

RTP Prognosis: Accelerated

Pain during outer-range strength test⁴² BAMIC grade 0⁶¹

Midrange strength as % of uninjured leg⁴² Shorter radiologist-predicted time to RTP⁶⁶

SLR flexibility of uninjured leg⁴² Shorter length of lesion⁶⁶

Greater physiotherapy attendance⁴² Smaller injury CSA⁶⁶

Shorter clinician-predicted time to RTP⁶⁶ MRI-negative injury^{9,10,33,37,62}

Lower grade of injury⁶⁶ Single muscle/tendon involvement²³

Sprinting-type vs stretching-type injury¹⁰ Lower % of muscle/tendon involvement²³

Lower radiologic grade of injury^23,29

Lower Cohen MRI score²³

Injuries not involving proximal tendon⁹

RTP Prognosis: No Effect

Sex⁴³ Craniocaudal length of injury^{6,7,8,26,42,57}

Dominant vs nondominant limb^2,42,43 Mediolateral width of injury^6,7,42

Sudden vs gradual pain onset⁴² Depth of injury^7,30

Injury during game vs training⁴² Volume of edema^7,26,57

Forced to cease activity within 5 min⁴² Tendon involvement^30,42

Ability to walk/jog pain-free⁴² Myofascial involvement^30,42

No. of days to walk pain-free^42,57 Muscle (most) involved^{24,29,30,37,42,57,61,75,82}

No. of days to ascend stairs pain-free⁸³ Injury CSA as % of total muscle CSA^26,42,57

Mechanism of injury^{2,42,57,82,83} Distance of injury from ischium^7,8,42,57,82

History of low back pain^42,82 Intra- or intermuscular hemorrhage⁶⁶

History of lower limb injury⁴² Site of injury within the muscle^23,30,61,75

History of lower limb surgery⁴² Grade 1 vs grade 2 injury^29,61

Pain on 1- or 2-leg squat⁴² MRI grade of injury⁵⁷

Pain on palpation of injured area^35,42 Presence of extramuscular fluid⁵⁷

Craniocaudal length of palpated pain^1,6,7,42,57 Partial disruption of the central tendon⁸⁰

Mediolateral width of palpated pain⁴² Amount of central tendon retraction⁸⁰

Distance of palpated pain from ischium^35,42,57 BAMIC type a vs b⁶¹

Location of point of highest palpated pain^7,8

Site of injury within the muscle^43,55,81,83

No. of muscles injured²

Positive vs negative slump test^82,83

Frequency of physiotherapy²

Grade of injury^2,43

Level of play/intensity of sport^2,57

Delay in seeking physiotherapy¹

Active knee extension deficit^1,57,83

Pain upon active knee extension⁵⁷

Pain upon PKE³⁵

Pain on passive SLR⁵⁷

Pain upon isometric contraction^35,83

Previous ACL graft harvesting⁵⁷

Isometric knee flexion strength^5,57

Hip ROM^5,83

Use of NSAIDs within 72 h of injury⁸³

RTP Prognosis: Delayed

Female sex² Volume of injury^6,42,75

Greater PKE range of uninjured leg⁴² Greater craniocaudal length of injury^{9,10,23,30,66,73}

Greater peak torque angle in knee extension⁴² Greater width of edema³⁰

Higher grade of injury⁶⁶ Greater length of lesion as % of height³³

Injury to biceps femoris⁶⁶ Greater depth of injury⁶

Shorter distance of pain to ischium^7,9,10 Longer radiologist-predicted time to RTP⁶⁶

Stretching-type vs sprinting-type injury^5,10 Larger injury CSA^{6,33,62,66,75}

Greater maximum pain at time of injury^42,82 Involvement of proximal tendon^6,10

Worst VAS pain score >6³⁵ Proximal vs distal injuries⁶

Higher VAS pain score at initial examination⁸¹ Shorter distance of injury to ischium^6,9,10

“Popping” sound at time of injury³⁵ Higher Cohen MRI score²³/score >10³⁹

Bruising³⁵ MRI-positive injury⁸¹

Greater deficit in passive SLR⁵⁷ Greater % of muscle/tendon involvement²³

Longer clinician-predicted time to RTP^66,81 Complete tendinous/myotendinous rupture⁶²

Forced to cease activity within 5 min⁸² Complete central tendon disruption^24,80

Greater length of palpated pain⁸² Presence of central tendon waviness⁸⁰

Pain on resisted knee flexion⁸² Greater central tendon retraction²³

>1 wk to initial consultation² Higher radiologic grade of injury^{23,29,30,37,61,82}

Recurrent muscle injury² Greater No. of muscles involved³⁹

Greater active knee ROM deficit^35,53 Distal tendinous or myotendinous injury⁶²

Longer self-predicted time to RTP⁵⁷ Peritendinous fluid collection⁶²

Lower level of sport⁸

>1 d to walk pain-free⁸³

^a ACL, anterior cruciate ligament; BAMIC, British Athletics Muscle Injury Classification; CSA, cross-sectional area; MRI, magnetic resonance imaging; NSAID, nonsteroidal anti-inflammatory drug; PKE, passive knee extension; ROM, range of motion; RTP, return to play; SLR, straight-leg raise; VAS, visual analog scale.

Clinical Factors

Seventeen studies investigated relationships between clinical assessment findings and time to RTP ^f. Pain during outer-range strength testing,⁴⁴ greater midrange strength as a percentage of uninjured leg strength,⁴⁴ and shorter clinician-predicted recovery⁶⁹ were associated with accelerated RTP. In contrast, factors associated with delayed RTP included greater passive knee extension of the uninjured leg,⁴⁴ greater peak torque angle in knee extension,⁴⁴ injury to the biceps femoris,⁶⁹ greater maximum pain at injury,^44,85 worst visual analog scale (VAS) pain score >6,³⁶ higher VAS pain score at initial examination,⁸⁴ popping sound at injury,³⁶ bruising,³⁶ pain on resisted knee flexion,⁸⁵ and longer clinician-^69,84 and self-predicted time to RTP.⁵⁹ Several examined factors had contradictory results across studies. Two studies by Askling et al^5,10 noted stretching-type injuries took longer to recover than did sprinting-type ones, while others found injury mechanism to have no effect on recovery time.^{2,44,59,85,86} There was no consensus regarding the effect on time to RTP for sex,^2,45 injury grade,^2,45,69 physiotherapy attendance,^1,2,44 hip ROM,^5,44,59,86 number of days to walk pain-free,^44,59,86 history of ipsilateral or contralateral lower limb injury,^{1,2,44,45,59,85,86} craniocaudal length of pain,^{1,6,7,44,59,85} need to cease activity within 5 minutes of injury,^44,85 level of play,^2,8,59 or active knee extension deficit.^{1,36,55,59,86}

MRI Factors

Twenty-three studies evaluated the role of MRI in predicting time to RTP.^g Accelerated RTP was associated with MRI-negative injury,^{9,10,34,38,64} lower percentage of muscle/tendon involvement,²⁴ and shorter radiologist-predicted recovery.⁶⁹ Conversely, the following were associated with prolonged recovery time: MRI-positive injury,⁸⁴ greater normalized length of lesion,³⁴ greater percentage of muscle/tendon involvement,²⁴ complete tendinous/myotendinous rupture,^63,64 complete central tendon disruption,^25,83 central tendon waviness,⁸³ greater number of muscles involved,⁴⁰ and longer radiologist-predicted recovery.⁶⁹ Studies reported conflicting results for injury grade,^{24,29,30,38,59,63,85} length,^h width,^6,7,30,44 depth,^6,7,30 cross-sectional area,^{6,27,34,44,59,64,69,78} volume,^{6,7,27,44,59,78} tendon involvement,^{6,9,10,24,30,44} amount of tendon retraction,^24,83 site of injury within the muscle,^{6,24,30,63,64,78} presence of extramuscular fluid,^59,64 distance from ischium,^{6

–10,44,59,85} and the Cohen MRI score.^24,40 Of note, the Cohen MRI score refers to an assessment tool designed to evaluate hamstring injuries on the basis of patient age, muscles involved, injury location, extent of injury, and retraction.²⁴

Discussion

This review assessed management of acute proximal and muscular hamstring injuries by reviewing interventions and prognostic factors associated with RTP. According to the literature, patients undergoing surgical treatment for partial or complete proximal hamstring ruptures achieved consistently better outcomes compared with those managed nonoperatively.^{11,12,15,19,68} For patients with acute muscular injuries, physiotherapy incorporating eccentric training^9,10,82 and PATS^73,76 attained favorable outcomes in time to RTP, reinjury rate, and restoration of strength. Stretching-based protocols increased ROM but failed to reduce reinjury risk or improve strength.^46,56,73 Supported by findings that rehabilitation with pain-threshold limits does not predispose to adverse effects,⁴¹ early initiation of rehabilitation enabled faster RTP.^14,45 Slump stretching⁴⁹ and reflexive release techniques³ also offered functional benefit by addressing neurological components of hamstring strain. Regarding the efficacy of PRP injection, results were inconclusive, confounded by a lack of standardization in PRP formulation and injection protocol. Similar inconsistencies have been reported in recent meta-analyses,^35,61,71,75 emphasizing the need to determine the optimal injection protocol for standard use in future research investigating the effect of PRP on time to RTP. Overall, although the quality of evidence of included studies varied, the diverse methods and predictive factors examined warrant consideration by clinicians seeking to optimize injury recovery.

Studies quantifying the prognostic value of baseline assessments have indicated that certain clinical and MRI findings are correlated with time to RTP. Clinical factors associated with accelerated RTP included lesser deficit in strength of the injured leg relative to the uninjured leg⁴⁴ and shorter physician-predicted recovery time,⁶⁹ whereas prolonged time to RTP was observed in patients with greater pain,^36,44,84,85 injury to the biceps femoris,⁶⁹ and longer physician-^69,84 and self-predicted⁵⁹ recovery times. It is possible that patients with greater strength and decreased pain in the injured leg at baseline may be able to begin physiotherapeutic activity and facilitate rehabilitation sooner after injury, resulting in earlier RTP. On MRI scans, findings indicating greater injury severity at initial presentation, such as greater lesion size,^24,34,84 tendinous/myotendinous rupture,^25,63,64,83 and greater number of muscles affected,⁴⁰ were correlated with prolonged RTP. Despite associations of initial examination and MRI findings with time to RTP, accurate prognostication of recovery time remains difficult. In a multivariate analysis of 180 patients, Wangensteen et al⁸⁵ determined that a single clinical examination at initial presentation accounted for 29% of variance in time to RTP, whereas supplementation with MRI findings explained only an additional 2.8%. Jacobsen et al⁴⁴ likewise reported that 59.0% and 8.6% of variance in RTP was accounted for by clinical and MRI examination, respectively, suggesting the added benefit of MRI findings in prognosticating RTP is less pronounced.

This study has several important limitations. First, the strength of any systematic review is dependent upon the quality of evidence of included studies. This review included 17 RCTs, of which 5 were determined as raising “some concerns” on risk-of-bias assessment. The remaining 58 studies consisted of cohort, case-control, and case series study designs included in an effort to be comprehensive in evaluating rehabilitative techniques. When critically appraised, comparative nonrandomized studies achieved a mean MINORS score of 18.8 ± 1.3, and noncomparative nonrandomized studies achieved a score of 11.4 ± 3.4. These scores indicate a reasonable risk of bias and are mainly attributable to a lack of prospective data collection, blinding, and/or prospective calculation of sample size. Differences in study design, patient population, and outcome measures limited direct comparisons between studies and precluded data pooling for meta-analyses, making it difficult to draw concrete conclusions in circumstances of conflicting results. This was particularly apparent when analyzing the efficacy of PRP injection for treatment of hamstring muscular injury, as studies varied in terms of volume, location, and number of injections. With regard to studies examining the prognostic value of clinical and MRI examination, the majority conducted only univariate analyses correlating baseline findings with RTP. Furthermore, criteria for RTP and methods of functional assessment were inconsistent, likely explaining some of the variance in time to RTP across studies. Future large-scale research using standardized RTP criteria and outcome measures are required to determine reliable associations between baseline findings and RTP prognosis via multivariate analysis.

Conclusion

Surgical intervention offers substantial benefits over nonoperative care for treatment of acute partial and complete proximal hamstring ruptures, while muscular injuries are effectively treated with physiotherapy encompassing eccentric training and PATS. The efficacy of PRP, however, remains controversial. Prognostication of RTP is of great importance, and the ability to accurately predict recovery time can be improved with a thorough clinical examination shortly after injury. Although the added benefit may be limited, structural factors observed on MRI scans can also inform RTP prognosis. Future high-quality research evaluating novel therapeutic protocols and prognostic determinants of RTP is needed to further enhance rehabilitation and better predict recovery timelines for athletes with acute hamstring injury.

	Studies of Proximal Hamstring Injury Management	Studies of Muscular Hamstring Injury Management
No. of patients	775	1057
Patient age, y, mean ± SD	42.4 ± 10.5	26.2 ± 6.5
Patient sex, % male	57.2	87.6

								Additional Outcomes
Arner (2019)⁴	9 (16)	Partial proximal hamstring avulsion	Surgical	64	333 (range, 150-1440)	—	78				X
Ayuob (2020)¹¹	12 (16)	Complete proximal semimembranosus rupture	Surgical	20	83.3 ± 39.9	0.0	35	X	X		X
Ayuob (2020)¹²	12 (16)	Partial/complete tear of proximal MTJ of long head of biceps	Surgical	64	93.8 ± 35.7	—	24	X	X		X
Barnett (2015)¹³	10 (16)	Partial/complete proximal hamstring avulsion	Surgical	38	—	—	54	X
Best (2019)¹⁵	9 (16)	Complete proximal hamstring avulsion	Surgical	49	—	—	28				X
Biedert (2015)¹⁷	9 (16)	Avulsion fracture of ischial tuberosity	Surgical	3	—	—	24				X
Birmingham (2011)¹⁸	11 (16)	Complete proximal hamstring avulsion	Surgical	23	294 (range, 90-1080)	—	43	X		X
Blakeney (2017)¹⁹	15 (16)	Partial/complete proximal hamstring avulsion	Surgical	96	—	—	34				X
Bowman (2013)²⁰	10 (16)	Partial proximal hamstring avulsion	Surgical	17	—	—	32				X
Chahal (2012)²³	9 (16)	Complete proximal hamstring avulsion	Surgical	13	—	—	24	X			X
Hofmann (2014)⁴²	9 (16)	Complete proximal hamstring avulsion	Nonoperative	17	—	—	31	X			X
Klingele (2002)⁴⁷	10 (16)	Complete proximal hamstring avulsion	Surgical	11	180 (range, 90-300)	—	34	X
Konan (2010)⁴⁸	12 (16)	Complete proximal hamstring avulsion	Surgical	10	175 (range, 126-455)	—	12	X		X
Lefevre (2013)⁵¹	18 (24)	Partial/complete proximal hamstring avulsion	Surgical	34	171 ± 48	—	27	X		X	X
Léger-St-Jean (2019)⁵²	12 (16)	Complete proximal hamstring avulsion	Surgical	22	120 (IQR, 60-240)	—	6				X
Lempainen (2006)⁵⁴	10 (16)	Partial proximal hamstring avulsion	Surgical	48	150 (range, 30-360)	—	36
Piposar (2017)⁶²	18 (24)	Partial/complete proximal hamstring avulsion	(1) Surgical(2) Nonoperative	1510	—	—	3035	X			X
Sandmann (2016)⁶⁸	11 (16)	Complete proximal hamstring avulsion	Surgical	16	180 (range, 120-270)	—	56	X	X		X
Shambaugh (2017)⁷²	17 (24)	Complete proximal hamstring avulsion	(1) Surgical(2) Nonoperative	1411	—	—	4330	X			X
Skaara (2013)⁷⁷	9 (16)	Partial proximal hamstring avulsion	Surgical	31	—	—	30	X		X	X
Subbu (2014)⁸¹	12 (16)	Complete proximal hamstring avulsion	Surgical	78	112 (range, 84-224)	0.0	24
Willinger (2020)⁸⁷	11 (16)	Partial/complete proximal hamstring avulsion	Surgical	71	—	—	56				X

								Additional Outcomes
A Hamid (2014)¹	Low	Grade 1	(1) PRP (1 × 3-mL direct injection 5 d postinjury(2) No injection	1414	26.7 ± 7.0 ^c 42.5 ± 20.6 ^c	—	—	X
Bezuglov (2019)¹⁶	Low	BAMIC 2a/2b	(1) PRP (1 × 8-mL direct injection <48 h postinjury)(2) Saline (1 × 8-mL direct injection <48 h postinjury)	2020	11.4 ± 1.2 ^c 21.3 ± 2.7 ^c	0.00.0	6
Bradley (2020)²¹	18 (24)	Cohen grade 2	(1) PRP (1-3 × 2- to 5-mL direct injections 1 wk apart)(2) No injection	3039	22.5 ± 20.125.7 ± 20.6	3.32.6	—
Gaballah (2018)³³	Low	Grade 2	(1) PRP (1 × 3-mL direct injection, 5-7 d postinjury)(2) No injection	89	Maximum, 27 ^c Maximum, 43 ^c	—	—	X
Guillodo (2015)³⁷	19 (24)	Grade 3	(1) PRP (1 × 3-mL direct injection <8 d postinjury)(2) No injection	1519	50.9 ± 10.752.8 ± 15.7	—	—
Hamilton (2015)³⁹	Low	Grade 1-2	(1) PRP (3 × 1-mL injections 1 cm apart, <5 d postinjury)(2) PPP (3 × 1-mL injections 1 cm apart, <5 d postinjury)(3) No injection	303030	21 (95% CI, 18-24) ^c 27 (95% CI, 21-33) ^c 25 (95% CI, 22-29)	7.710.710.3	6	X
Lee (2020)⁵⁰	12 (16)	Grade 1-3	PRP (single injection)	8	49 (range, 10-112)	—	—
Rettig (2013)⁶⁵	18 (24)	Grade 1-2	(1) PRP (1 × 9-mL direct injection <48 h postinjury)(2) No injection	55	20 (range, 16-30)17 (range, 8-81)	—	—
Reurink (2015)⁶⁶	Low	Grade 1-2	(1) PRP (3 × 1-mL injections 1 cm apart at 5 and 10 d postinjury)(2) Saline (3 × 1-mL injections 1 cm apart at 5 and 10 d postinjury)	4139	42 (IQR, 30-58)42 (IQR, 37-56)	27.029.7	12	X	X
Wright-Carpenter (2004)⁸⁸	19 (24)	Grade 2	(1) Autologous conditioned serum (5 × 1-mL injections over area of injury every 2nd day [mean, 5.4 injections])(2) Actovegin/Traumeel therapy (5 × 1-mL injections over area of injury every second day [mean, 8.3 injections])	65	16.3 ± 3.1 ^c 21.8 ± 4.8 ^c	—	—
Zanon (2016)⁸⁹	12 (16)	Grade 2	PRP (2-3 × 3-mL injections at 72 h and 7 d postinjury)	25	35.1 ± 18.9	12.0	37

								Additional Outcomes
Albertin (2020)³	10 (16)	Grade 2	Primal Reflex Release Technique	6	—	—	—		X		X
Askling (2013)¹⁰	Some concerns	Sprinting or stretching	(1) L-protocol(2) C-protocol	3738	28 ± 15 ^c 51 ± 21 ^c	0.02.6	12
Askling (2014)⁹	Some concerns	Sprinting or stretching	(1) L-protocol(2) C-protocol	2828	49 ± 26 ^c 86 ± 34 ^c	0.07.1	12
Bayer (2018)¹⁴	Low	Munich type 3-4	(1) Early rehab(2) Delayed rehab	2022	62.5 (IQR, 48.8-77.8) ^d 83.0 (IQR, 64.5-97.3) ^d	9.10.0	12	X		X
Hickey (2020)⁴¹	Low	Grade 1-2	(1) Pain-threshold rehab(2) Pain-free rehab	2122	17 (95% CI, 11-24)15 (95% CI, 13-17)	9.59.1	6	X
Kilcoyne (2011)⁴⁵	10 (16)	Grade 1-2	Early, progressive rehab	48	11.9 (range, 5-23)	6.3	6
Kim (2018)⁴⁶	Some concerns	Grade 2	Stretching and ROM-based rehab	13	—	—	2	X	X
Kornberg (1989)⁴⁹	Some concerns	Grade 1	(1) Slump stretching(2) Standard rehab	1216	1 absent >1 game ^c 16 absent >1 game ^c	—	—
Malliaropoulos (2004)⁵⁶	Low	Grade 2	(1) 1× daily stretching(2) 4× daily stretching	4040	15.1 ± 0.8 ^c 13.3 ± 0.7 ^c	—	—		X
Medeiros (2020)⁵⁷	Low	Grade 1-2	(1) LLLT protocol(2) Standard rehab	1111	23.1 ± 9.123.8 ± 12.6	0.00.0	6	X	X
Mendiguchia (2017)⁵⁸	Low	Grade 1	(1) Rehab algorithm(2) Rehab protocol	2424	25.5 ± 7.823.2 ± 11.7	4.2 ^d 25.0 ^d	6
Sefiddhashti (2018)⁷⁰	Some concerns	Grade 1-2	(1) Cryotherapy with stretching(2) Cryotherapy alone	1819	—	—	0.25		X		X
Sherry (2004)⁷³	Low	Grade 1-2	(1) STST protocol(2) PATS protocol	1113	37.4 ± 27.622.2 ± 8.3	70.0 ^c 7.7 ^c	12
Silder (2013)⁷⁶	Low	Grade 1-2	(1) PATS protocol(2) PRES protocol	1312	28.8 ± 11.425.2 ± 6.3	16.723.1	12	X
Tyler (2017)⁸²	11 (16)	Grade 1-3	Eccentric strength protocol	50	77 ± 70	8.0	24	X

			Assessment
A Hamid (2014)¹	Low	28	X
A Hamid (2013)²	10 (16)	360	X
Askling (2006)⁵	12 (16)	33	X
Askling (2007)⁶	14 (16)	15	X	X
Askling (2007)⁷	14 (16)	18	X	X
Askling (2008)⁸	11 (16)	30	X	X
Askling (2014)⁹	Some concerns	56	X	X
Askling (2013)¹⁰	Some concerns	75	X	X
Cohen (2011)²⁴	14 (16)	38		X
Comin (2013)²⁵	20 (24)	62		X
Crema (2018)²⁷	11 (16)	22		X
Ekstrand (2012)²⁹	12 (16)	207		X
Ekstrand (2016)³⁰	12 (16)	255		X
Gibbs (2004)³³	12 (16)	31		X
Guillodo (2014)³⁶	12 (16)	128	X
Hallen (2014)³⁷	13 (16)	386		X
Hamilton (2018)⁴⁰	13 (16)	110		X
Jacobsen (2016)⁴⁴	14 (16)	90	X	X
Kilcoyne (2011)⁴⁵	10 (16)	48	X
Malliaropoulos (2010)⁵⁵	21 (24)	165	X
Moen (2014)⁵⁹	13 (16)	74	X	X
Pollock (2016)⁶³	11 (16)	44		X
Pomeranz (1993)⁶⁴	10 (16)	14		X
Schneider-Kolsky (2006)⁶⁹	21 (24)	58	X	X
Silder (2013)⁷⁶	Low	25		X
Slavotinek (2002)⁷⁵	12 (16)	30		X
van der Made (2018)⁸⁰	14 (16)	70		X
Verrall (2003)⁸¹	12 (16)	83	X	X
Wangensteen (2015)⁸²	11 (16)	180	X	X
Warren (2010)⁸³	13 (16)	59	X

Clinical Factors	MRI Factors
RTP Prognosis: Accelerated
Pain during outer-range strength test⁴²	BAMIC grade 0⁶¹
Midrange strength as % of uninjured leg⁴²	Shorter radiologist-predicted time to RTP⁶⁶
SLR flexibility of uninjured leg⁴²	Shorter length of lesion⁶⁶
Greater physiotherapy attendance⁴²	Smaller injury CSA⁶⁶
Shorter clinician-predicted time to RTP⁶⁶	MRI-negative injury^{9,10,33,37,62}
Lower grade of injury⁶⁶	Single muscle/tendon involvement²³
Sprinting-type vs stretching-type injury¹⁰	Lower % of muscle/tendon involvement²³
	Lower radiologic grade of injury^23,29
	Lower Cohen MRI score²³
	Injuries not involving proximal tendon⁹
RTP Prognosis: No Effect
Sex⁴³	Craniocaudal length of injury^{6,7,8,26,42,57}
Dominant vs nondominant limb^2,42,43	Mediolateral width of injury^6,7,42
Sudden vs gradual pain onset⁴²	Depth of injury^7,30
Injury during game vs training⁴²	Volume of edema^7,26,57
Forced to cease activity within 5 min⁴²	Tendon involvement^30,42
Ability to walk/jog pain-free⁴²	Myofascial involvement^30,42
No. of days to walk pain-free^42,57	Muscle (most) involved^{24,29,30,37,42,57,61,75,82}
No. of days to ascend stairs pain-free⁸³	Injury CSA as % of total muscle CSA^26,42,57
Mechanism of injury^{2,42,57,82,83}	Distance of injury from ischium^7,8,42,57,82
History of low back pain^42,82	Intra- or intermuscular hemorrhage⁶⁶
History of lower limb injury⁴²	Site of injury within the muscle^23,30,61,75
History of lower limb surgery⁴²	Grade 1 vs grade 2 injury^29,61
Pain on 1- or 2-leg squat⁴²	MRI grade of injury⁵⁷
Pain on palpation of injured area^35,42	Presence of extramuscular fluid⁵⁷
Craniocaudal length of palpated pain^1,6,7,42,57	Partial disruption of the central tendon⁸⁰
Mediolateral width of palpated pain⁴²	Amount of central tendon retraction⁸⁰
Distance of palpated pain from ischium^35,42,57	BAMIC type a vs b⁶¹
Location of point of highest palpated pain^7,8
Site of injury within the muscle^43,55,81,83
No. of muscles injured²
Positive vs negative slump test^82,83
Frequency of physiotherapy²
Grade of injury^2,43
Level of play/intensity of sport^2,57
Delay in seeking physiotherapy¹
Active knee extension deficit^1,57,83
Pain upon active knee extension⁵⁷
Pain upon PKE³⁵
Pain on passive SLR⁵⁷
Pain upon isometric contraction^35,83
Previous ACL graft harvesting⁵⁷
Isometric knee flexion strength^5,57
Hip ROM^5,83
Use of NSAIDs within 72 h of injury⁸³
RTP Prognosis: Delayed
Female sex²	Volume of injury^6,42,75
Greater PKE range of uninjured leg⁴²	Greater craniocaudal length of injury^{9,10,23,30,66,73}
Greater peak torque angle in knee extension⁴²	Greater width of edema³⁰
Higher grade of injury⁶⁶	Greater length of lesion as % of height³³
Injury to biceps femoris⁶⁶	Greater depth of injury⁶
Shorter distance of pain to ischium^7,9,10	Longer radiologist-predicted time to RTP⁶⁶
Stretching-type vs sprinting-type injury^5,10	Larger injury CSA^{6,33,62,66,75}
Greater maximum pain at time of injury^42,82	Involvement of proximal tendon^6,10
Worst VAS pain score >6³⁵	Proximal vs distal injuries⁶
Higher VAS pain score at initial examination⁸¹	Shorter distance of injury to ischium^6,9,10
“Popping” sound at time of injury³⁵	Higher Cohen MRI score²³/score >10³⁹
Bruising³⁵	MRI-positive injury⁸¹
Greater deficit in passive SLR⁵⁷	Greater % of muscle/tendon involvement²³
Longer clinician-predicted time to RTP^66,81	Complete tendinous/myotendinous rupture⁶²
Forced to cease activity within 5 min⁸²	Complete central tendon disruption^24,80
Greater length of palpated pain⁸²	Presence of central tendon waviness⁸⁰
Pain on resisted knee flexion⁸²	Greater central tendon retraction²³
>1 wk to initial consultation²	Higher radiologic grade of injury^{23,29,30,37,61,82}
Recurrent muscle injury²	Greater No. of muscles involved³⁹
Greater active knee ROM deficit^35,53	Distal tendinous or myotendinous injury⁶²
Longer self-predicted time to RTP⁵⁷	Peritendinous fluid collection⁶²
Lower level of sport⁸
>1 d to walk pain-free⁸³

Footnotes

Final revision submitted July 5, 2021; accepted August 10, 2021.

One or more of the authors has declared the following potential conflict of interest or source of funding: Funding was provided by the Conine Family Fund for Joint Preservation. S.D.M. has received education payments from Kairos Surgical and honoraria from Allergan. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Notes

APPENDIX

TABLE A1

Search Strategy

MEDLINE (Ovid)

Exp Hamstring muscles/

((hamstring* or (biceps adj2 femoris) or semimembranosus or semitendinosus or thigh or (posterior adj2 thigh)) not ACL not cruciate).tw, kw

1 or 2

Exp “Wounds and Injuries”/

Exp “Sprains and Strains”/

Exp Pain/

(injur* or (leg adj2 injur*) or (sports adj2 injur*) or (athletic adj2 injur*) or strain* or sprain* or tear* or ruptur* or trauma* or pain* or dysfunction*).tw, kw

4 or 5 or 6 or 7

Exp Therapeutics/

Exp Rehabilitation/

Exp Diagnostic Imaging/

(therap* or rehab* or manag* or interven* or imag*).tw, kw

9 or 10 or 11 or 12 or 13

Exp “Recovery of Function”/

Exp Sports Medicine/

(recover* or progress* or convalescen* or outcome* or “return to play” or “return to sport” or “return to competition” or “return to participation” or “return to training” or “return-to-play” or “return-to-sport” or “return-to-competition” or “return-to-participation” or “return-to-training”).tw, kw

(re-occur* or recur* or reoccur* or re-inj* or reinj*).tw, kw

14 or 15 or 16 or 17

3 and 8 and 13 and 18

Limit 19 to (English language and full text)

Limit 20 to MEDLINE

CINAHL (EBSCO)

(MH “hamstring muscles” OR MH thigh OR TI ((hamstring* or (biceps N2 femoris) or semimembranosus or semitendinosus or thigh or (posterior N2 thigh))) OR AB ((hamstring* or (biceps N2 femoris) or semimembranosus or semitendinosus or thigh or (posterior N2 thigh)))) NOT TI ACL NOT TI cruciate

MH (“Wounds and Injuries”) OR MH (“Sprains and Strains”) OR MH “Pain” or TI ((injur* or (leg N2 injur*) or (sports N2 injur*) or (athletic N2 injur*) or strain* or sprain* or tear* or rupture* or trauma* or pain* or dysfunction*)) OR AB ((injur* or (leg N2 injur*) or (sports N2 injur*) or (athletic N2 injur*) or strain* or sprain* or tear* or rupture* or trauma* or pain* or dysfunction*))

MH Therapeutics OR MH Rehabilitation OR MH “Diagnostic Imaging” OR TI ((therap* or rehab* or manag* or interven* or imag*)) OR AB ((therap* or rehab* or manag* or interven* or imag*))

MH “Recovery of Function” OR MH “Sports Medicine” OR TI ((recover* or progress* or convalescen* or outcome* or “return to play” or “return to sport” or “return to competition” or “return to participat*” or “return to train*” or “return-to-play” or “return-to-sport” or “return-to-competition” or “return-to-participat*” or “return-to-train*”)) OR AB ((recover* or progress* or convalescen* or outcome* or “return to play” or “return to sport” or “return to competition” or “return to participat*” or “return to train*” or “return-to-play” or “return-to-sport” or “return-to-competition” or “return-to-participat*” or “return-to-train*”))

S1 AND S2 AND S3 AND S4

Narrow by language – English

Limiters – full text

Cochrane Central Register for Controlled Trials (EBSCO)

MH Therapeutics OR MH Rehabilitation OR MH “Diagnostic Imaging” OR TI ((therap* or rehab* or manag* or interven* or imag*)) OR AB ((therap* or rehab* or manag* or interven* or imag*))

S1 AND S2 AND S3 AND S4

Narrow by language – English

SPORTDiscus (EBSCO)

MH Therapeutics OR MH Rehabilitation OR MH “Diagnostic Imaging” OR TI ((therap* or rehab* or manag* or interven* or imag*)) OR AB ((therap* or rehab* or manag* or interven* or imag*))

S1 AND S2 AND S3 AND S4

Narrow by Language – English

Limiters – Full Text

References

A Hamid

Mohamed Ali

Yusof

George

Lee

LPC

. Platelet-rich plasma injections for the treatment of hamstring injuries: a randomized controlled trial. Am J Sports Med. 2014;42(10):2410–2418.

A Hamid

Yusof

Mohamed Ali

. Pattern of muscle injuries and predictors of return-to-play duration among Malaysian athletes. Singapore Med J. 2013;54(10):587–591.

Albertin

Walters

May

Baker

Nasypany

Cheatham

. An exploratory case series analysis of the use of Primal Reflex Release Technique™ to improve signs and symptoms of hamstring strain. Int J Sports Phys Ther. 2020;15(2):263–273.

Arner

Freiman

Mauro

Bradley

. Functional results and outcomes after repair of partial proximal hamstring avulsions at midterm follow-up. Am J Sports Med. 2019;47(14):3436–3443.

Askling

Saartok

Thorstensson

. Type of acute hamstring strain affects flexibility, strength, and time to return to pre-injury level. Br J Sports Med. 2006;40(1):40–44.

Askling

Tengvar

Saartok

Thorstensson

. Acute first-time hamstring strains during high-speed running: a longitudinal study including clinical and magnetic resonance imaging findings. Am J Sports Med. 2007;35(2):197–206.

Askling

Tengvar

Saartok

Thorstensson

. Acute first-time hamstring strains during slow-speed stretching: clinical, magnetic resonance imaging, and recovery characteristics. Am J Sports Med. 2007;35(10):1716–1724.

Askling

Tengvar

Saartok

Thorstensson

. Proximal hamstring strains of stretching type in different sports. Am J Sports Med. 2008;36(9):1799–1804.

Askling

Tengvar

Tarassova

Thorstensson

. Acute hamstring injuries in Swedish elite sprinters and jumpers: a prospective randomised controlled clinical trial comparing two rehabilitation protocols. Br J Sports Med. 2014;48(7):532–539.

10.

Askling

Tengvar

Thorstensson

. Acute hamstring injuries in Swedish elite football: a prospective randomised controlled clinical trial comparing two rehabilitation protocols. Br J Sports Med. 2013;47(15):953–959.

11.

Ayuob

Kayani

Haddad

. Acute surgical repair of complete, nonavulsion proximal semimembranosus injuries in professional athletes. Am J Sports Med. 2020;48(9):2170–2177.

12.

Ayuob

Kayani

Haddad

. Musculotendinous junction injuries of the proximal biceps femoris: a prospective study of 64 patients treated surgically. Am J Sports Med. 2020;48(8):1974–1982.

13.

Barnett

Negus

Barton

Wood

. Reattachment of the proximal hamstring origin: outcome in patients with partial and complete tears. Knee Surg Sports Traumatol Arthrosc. 2015;23(7):2130–2135.

14.

Bayer

Hoegberget-Kalisz

Jensen

, et al. Role of tissue perfusion, muscle strength recovery, and pain in rehabilitation after acute muscle strain injury: a randomized controlled trial comparing early and delayed rehabilitation. Scand J Med Sci Sports. 2018;28(12):2579–2591.

15.

Best

Eberle

Beck

Beckmann

Becker

. Functional impairment after successful surgical reconstruction for proximal hamstring avulsion. Int Orthop. 2019;43(10):2341–2347.

16.

Bezuglov

Maffulli

Tokareva

Achkasov

. Platelet-rich plasma in hamstring muscle injuries in professional soccer players: a pilot study. Muscles Ligaments Tendons J. 2019;9(1):112–118.

17.

Biedert

. Surgical management of traumatic avulsion of the ischial tuberosity in young athletes. Clin J Sport Med. 2015;25(1):67–72.

18.

Birmingham

Muller

Wickiewicz

Cavanaugh

Rodeo

Warren

. Functional outcome after repair of proximal hamstring avulsions. J Bone Joint Surg Am. 2011;93(19):1819–1826.

19.

Blakeney

Zilko

Edmonston

Schupp

Annear

. A prospective evaluation of proximal hamstring tendon avulsions: improved functional outcomes following surgical repair. Knee Surg Sports Traumatol Arthrosc. 2017;25(6):1943–1950.

20.

Bowman

Cohen

Bradley

. Operative management of partial-thickness tears of the proximal hamstring muscles in athletes. Am J Sports Med. 2013;41(6):1363–1371.

21.

Bradley

Lawyer

Ruef

Towers

Arner

. Platelet-rich plasma shortens return to play in National Football League players with acute hamstring injuries. Orthop J Sports Med. 2020;8(4):2325967120911731.

22.

Carlson

. The natural history and management of hamstring injuries. Curr Rev Musculoskelet Med. 2008;1(2):120–123.

23.

Chahal

Bush-Joseph

Chow

, et al.

Clinical and magnetic resonance imaging outcomes after surgical repair of complete proximal hamstring ruptures: does the tendon heal?

Am J Sports Med. 2012;40(10):2325–2330.

24.

Cohen

Towers

Zoga

, et al. Hamstring injuries in professional football players: magnetic resonance imaging correlation with return to play. Sports Health. 2011;3(5):423–430.

25.

Comin

Malliaras

Baquie

Barbour

Connell

. Return to competitive play after hamstring injuries involving disruption of the central tendon. Am J Sports Med. 2013;41(1):111–115.

26.

Cooper

Conway

. Distal semitendinosus ruptures in elite-level athletes. Am J Sports Med. 2010;38(6):1174–1178.

27.

Crema

Godoy

IRB

Abdalla

de Aquino

Ingham

SJM

Skaf

. Hamstring injuries in professional soccer players: extent of MRI-detected edema and the time to return to play. Sports Health. 2018;10(1):75–79.

28.

Cumpston

Page

, et al. Updated guidance for trusted systematic reviews: a new edition of the Cochrane Handbook for Systematic Reviews of Interventions. Cochrane Database Syst Rev. 2019;10:ED000142.

29.

Ekstrand

Healy

Waldén

Lee

English

Hägglund

. Hamstring muscle injuries in professional football: the correlation of MRI findings with return to play. Br J Sports Med. 2012;46(2):112–117.

30.

Ekstrand

Lee

Healy

. MRI findings and return to play in football: a prospective analysis of 255 hamstring injuries in the UEFA Elite Club Injury Study. Br J Sports Med. 2016;50(12):738–743.

31.

Ekstrand

Waldén

Hägglund

. Hamstring injuries have increased by 4% annually in men’s professional football, since 2001: a 13-year longitudinal analysis of the UEFA Elite Club Injury Study. Br J Sports Med. 2016;50(12):731–737.

32.

Engebretsen

Myklebust

Holme

Engebretsen

Bahr

. Intrinsic risk factors for hamstring injuries among male soccer players: a prospective cohort study. Am J Sports Med. 2010;38(6):1147–1153.

33.

Gaballah

Elgeidi

Bressel

Shakrah

Abd-Alghany

. Rehabilitation of hamstring strains: does a single injection of platelet-rich plasma improve outcomes? (Clinical study). Sport Sci Health. 2018;14(2):439–447.

34.

Gibbs

Cross

Cameron

Houang

. The accuracy of MRI in predicting recovery and recurrence of acute grade one hamstring muscle strains within the same season in Australian Rules football players. J Sci Med Sport. 2004;7(2):248–258.

35.

Grassi

Napoli

Romandini

, et al. Is platelet-rich plasma (PRP) effective in the treatment of acute muscle injuries? A systematic review and meta-analysis. Sports Med. 2018;48(4):971–989.

36.

Guillodo

Here-Dorignac

Thoribé

, et al. Clinical predictors of time to return to competition following hamstring injuries. Muscles Ligaments Tendons J. 2014;4(3):386–390.

37.

Guillodo

Madouas

Simon

Le Dauphin

Saraux

. Platelet-rich plasma (PRP) treatment of sports-related severe acute hamstring injuries. Muscles Ligaments Tendons J . 2015;5(4):284–288.

38.

Hallén

Ekstrand

. Return to play following muscle injuries in professional footballers. J Sports Sci. 2014;32(13):1229–1236.

39.

Hamilton

Tol

Almusa

, et al. Platelet-rich plasma does not enhance return to play in hamstring injuries: a randomised controlled trial. Br J Sports Med. 2015;49(14):943–950.

40.

Hamilton

Wangensteen

Whiteley

, et al. Cohen’s MRI scoring system has limited value in predicting return to play. Knee Surg Sports Traumatol Arthrosc. 2018;26(4):1288–1294.

41.

Hickey

Timmins

Maniar

, et al. Pain-free versus pain-threshold rehabilitation following acute hamstring strain injury: a randomized controlled trial. J Orthop Sports Phys Ther. 2020;50(2):91–103.

42.

Hofmann

Paggi

Connors

Miller

. Complete avulsion of the proximal hamstring insertion: functional outcomes after nonsurgical treatment. J Bone Joint Surg Am. 2014;96(12):1022–1025.

43.

Irger

Willinger

Lacheta

Pogorzelski

Imhoff

Feucht

. Proximal hamstring tendon avulsion injuries occur predominately in middle-aged patients with distinct gender differences: epidemiologic analysis of 263 surgically treated cases. Knee Surg Sports Traumatol Arthrosc. 2020;28(4):1221–1229.

44.

Jacobsen

Witvrouw

Muxart

Tol

Whiteley

. A combination of initial and follow-up physiotherapist examination predicts physician-determined time to return to play after hamstring injury, with no added value of MRI. Br J Sports Med. 2016;50(7):431–439.

45.

Kilcoyne

Dickens

Keblish

Rue

J-P

Chronister

. Outcome of grade I and II hamstring injuries in intercollegiate athletes: a novel rehabilitation protocol. Sports Health. 2011;3(6):528–533.

46.

Kim

. Effect of stretching-based rehabilitation on pain, flexibility and muscle strength in dancers with hamstring injury: a single-blind, prospective, randomized clinical trial. J Sports Med Phys Fitness. 2018;58(9):1287–1295.

47.

Klingele

Sallay

. Surgical repair of complete proximal hamstring tendon rupture. Am J Sports Med. 2002;30(5):742–747.

48.

Konan

Haddad

. Successful return to high level sports following early surgical repair of complete tears of the proximal hamstring tendons. Int Orthop. 2010;34(1):119–123.

49.

Kornberg

Lew

. The effect of stretching neural structures on grade one hamstring injuries. J Orthop Sports Phys Ther. 1989;10(12):481–487.

50.

Lee

Baker

Hanaoka

Tjong

Terry

. Treatment of patellar and hamstring tendinopathy with platelet-rich plasma in varsity collegiate athletes: a case series. J Orthop. 2020;18:91–94.

51.

Lefevre

Bohu

Naouri

Klouche

Herman

. Returning to sports after surgical repair of acute proximal hamstring ruptures. Knee Surg Sports Traumatol Arthrosc. 2013;21(3):534–539.

52.

Léger-St-Jean

Gorica

Magnussen

Vasileff

Kaeding

. Accelerated rehabilitation results in good outcomes following acute repair of proximal hamstring ruptures. Knee Surg Sports Traumatol Arthrosc. 2019;27(10):3121–3124.

53.

Lempainen

Kosola

Pruna

, et al. Central tendon injuries of hamstring muscles: case series of operative treatment. Orthop J Sports Med. 2018;6(2):2325967118755992.

54.

Lempainen

Sarimo

Heikkila

Mattila

Orava

. Surgical treatment of partial tears of the proximal origin of the hamstring muscles. Br J Sports Med. 2006;40(8):688–691.

55.

Malliaropoulos

Papacostas

Kiritsi

Papalada

Gougoulias

Maffulli

. Posterior thigh muscle injuries in elite track and field athletes. Am J Sports Med. 2010;38(9):1813–1819.

56.

Malliaropoulos

Papalexandris

Papalada

Papacostas

. The role of stretching in rehabilitation of hamstring injuries: 80 athletes follow-up. Med Sci Sports Exerc. 2004;36(5):756–759.

57.

Medeiros

Aimi

Vaz

Baroni

. Effects of low-level laser therapy on hamstring strain injury rehabilitation: a randomized controlled trial. Phys Ther Sport. 2020;42:124–130.

58.

Mendiguchia

Martinez-Ruiz

Edouard

, et al. A multifactorial, criteria-based progressive algorithm for hamstring injury treatment. Med Sci Sports Exerc. 2017;49(7):1482–1492.

59.

Moen

Reurink

Weir

Tol

Maas

Goudswaard

. Predicting return to play after hamstring injuries. Br J Sports Med. 2014;48(18):1358–1363.

60.

Moher

Liberati

Tetzlaff

Altman

; the PRISMA Group. Preferred Reporting Items for Systematic Reviews and Meta-Analyses: the PRISMA statement. PLoS Med. 2009;6(7):e1000097.

61.

Pas

Reurink

Tol

Weir

Winters

Moen

. Efficacy of rehabilitation (lengthening) exercises, platelet-rich plasma injections, and other conservative interventions in acute hamstring injuries: an updated systematic review and meta-analysis. Br J Sports Med. 2015;49(18):1197–1205.

62.

Piposar

Vinod

Olsen

Lacerte

Miller

. High-grade partial and retracted (<2 cm) proximal hamstring ruptures. Orthop J Sports Med. 2017;5(2):2325967117692507.

63.

Pollock

Patel

Chakraverty

Suokas

James

Chakraverty

. Time to return to full training is delayed and recurrence rate is higher in intratendinous (“c”) acute hamstring injury in elite track and field athletes: clinical application of the British Athletics Muscle Injury Classification. Br J Sports Med. 2016;50(5):305–310.

64.

Pomeranz

Heidt

MR imaging in the prognostication of hamstring injury: work in progress. Radiology. 1993;189(3):897–900.

65.

Rettig

Meyer

Bhadra

. Platelet-rich plasma in addition to rehabilitation for acute hamstring injuries in NFL players: clinical effects and time to return to play. Orthop J Sports Med. 2013;1(1):2325967113494354.

66.

Reurink

Goudswaard

Moen

, et al. Rationale, secondary outcome scores and 1-year follow-up of a randomised trial of platelet-rich plasma injections in acute hamstring muscle injury: the Dutch Hamstring Injection Therapy study. Br J Sports Med. 2015;49(18):1206–1212.

67.

Ribeiro-Alvares

Marques

Vaz

Baroni

. Four weeks of Nordic hamstring exercise reduce muscle injury risk factors in young adults. J Strength Cond Res. 2018;32(5):1254–1262.

68.

Sandmann

Hahn

Amereller

, et al. Mid-term functional outcome and return to sports after proximal hamstring tendon repair. Int J Sports Med. 2016;37(7):570–576.

69.

Schneider-Kolsky

Hoving

Warren

Connell

. A comparison between clinical assessment and magnetic resonance imaging of acute hamstring injuries. Am J Sports Med. 2006;34(6):1008–1015.

70.

Sefiddashti

Ghotbi

Salavati

Farhadi

Mazaheri

. The effects of cryotherapy versus cryostretching on clinical and functional outcomes in athletes with acute hamstring strain. J Bodyw Mov Ther. 2018;22(3):805–809.

71.

Seow

Shimozono

Tengku Yusof

TNB

Yasui

Massey

Kennedy

. Platelet-rich plasma injection for the treatment of hamstring injuries: a systematic review and meta-analysis with best-worst case analysis. Am J Sports Med. 2021;49(2):529–537.

72.

Shambaugh

Olsen

Kellum

Lacerte

Miller

. A comparison of nonoperative and operative treatment of complete proximal hamstring ruptures. Orthop J Sports Med. 2017;5(11):2325967117738551.

73.

Sherry

Best

. A comparison of 2 rehabilitation programs in the treatment of acute hamstring strains. J Orthop Sports Phys Ther. 2004;34(3):116–125.

74.

Sherry

Johnston

Heiderscheit

. Rehabilitation of acute hamstring strain injuries. Clin Sports Med. 2015;34(2):263–284.

75.

Sheth

Dwyer

Smith

, et al.

Does platelet-rich plasma lead to earlier return to sport when compared with conservative treatment in acute muscle injuries? A systematic review and meta-analysis.

Arthroscopy. 2018;34(1):281–288.e281.

76.

Silder

Sherry

Sanfilippo

Tuite

Hetzel

Heiderscheit

. Clinical and morphological changes following 2 rehabilitation programs for acute hamstring strain injuries: a randomized clinical trial. J Orthop Sports Phys Ther. 2013;43(5):284–299.

77.

Skaara

Moksnes

Frihagen

Stuge

. Self-reported and performance-based functional outcomes after surgical repair of proximal hamstring avulsions. Am J Sports Med. 2013;41(11):2577–2584.

78.

Slavotinek

Verrall

Fon

. Hamstring injury in athletes: using MR imaging measurements to compare extent of muscle injury with amount of time lost from competition. AJR Am J Roentgenol. 2002;179(6):1621–1628.

79.

Slim

Nini

Forestier

Kwiatkowski

Panis

Chipponi

. Methodological Index for Non-Randomized Studies (MINORS): development and validation of a new instrument. ANZ J Surg. 2003;73(9):712–716.

80.

Sterne

JAC

Savovic

Page

, et al. RoB 2: a revised tool for assessing risk of bias in randomised trials. BMJ. 2019;366:l4898.

81.

Subbu

Benjamin-Laing

Haddad

. Timing of surgery for complete proximal hamstring avulsion injuries: successful clinical outcomes at 6 weeks, 6 months, and after 6 months of injury. Am J Sports Med. 2015;43(2):385–391.

82.

Tyler

Schmitt

Nicholas

McHugh

. Rehabilitation after hamstring-strain injury emphasizing eccentric strengthening at long muscle lengths: results of long-term follow-up. J Sport Rehabil. 2017;26(2):131–140.

83.

van der Made

Almusa

Whiteley

, et al. Intramuscular tendon involvement on MRI has limited value for predicting time to return to play following acute hamstring injury. Br J Sports Med. 2018;52(2):83–88.

84.

Verrall

Slavotinek

Barnes

Fon

. Diagnostic and prognostic value of clinical findings in 83 athletes with posterior thigh injury: comparison of clinical findings with magnetic resonance imaging documentation of hamstring muscle strain. Am J Sports Med. 2003;31(6):969–973.

85.

Wangensteen

Almusa

Boukarroum

, et al. MRI does not add value over and above patient history and clinical examination in predicting time to return to sport after acute hamstring injuries: a prospective cohort of 180 male athletes. Br J Sports Med. 2015;49(24):1579–1587.

86.

Warren

Gabbe

Schneider-Kolsky

Bennell

. Clinical predictors of time to return to competition and of recurrence following hamstring strain in elite Australian footballers. Br J Sports Med. 2010;44(6):415–419.

87.

Willinger

Siebenlist

Lacheta

, et al. Excellent clinical outcome and low complication rate after proximal hamstring tendon repair at mid-term follow up. Knee Surg Sports Traumatol Arthrosc. 2020;28(4):1230–1235.

88.

Wright-Carpenter

Klein

Schaferhoff

Appell

Mir

Wehling

. Treatment of muscle injuries by local administration of autologous conditioned serum: a pilot study on sportsmen with muscle strains. Int J Sports Med. 2004;25(8):588–593.

89.

Zanon

Combi

Perticarini

Sammarchi

Benazzo

. Platelet-rich plasma in the treatment of acute hamstring injuries in professional football players. Joints. 2016;4(1):17–23.

								Additional Outcomes
Lead Author (Year)	Risk of Bias ^b	Injury Type	Intervention	N	Mean ± SD Time to RTP, d	Reinjury Rate, %	Mean Follow-up, mo	Hamstring Strength	Hamstring ROM	H:Q Ratio	Functional Assessment
Arner (2019)⁴	9 (16)	Partial proximal hamstring avulsion	Surgical	64	333 (range, 150-1440)	—	78				X
Ayuob (2020)¹¹	12 (16)	Complete proximal semimembranosus rupture	Surgical	20	83.3 ± 39.9	0.0	35	X	X		X
Ayuob (2020)¹²	12 (16)	Partial/complete tear of proximal MTJ of long head of biceps	Surgical	64	93.8 ± 35.7	—	24	X	X		X
Barnett (2015)¹³	10 (16)	Partial/complete proximal hamstring avulsion	Surgical	38	—	—	54	X
Best (2019)¹⁵	9 (16)	Complete proximal hamstring avulsion	Surgical	49	—	—	28				X
Biedert (2015)¹⁷	9 (16)	Avulsion fracture of ischial tuberosity	Surgical	3	—	—	24				X
Birmingham (2011)¹⁸	11 (16)	Complete proximal hamstring avulsion	Surgical	23	294 (range, 90-1080)	—	43	X		X
Blakeney (2017)¹⁹	15 (16)	Partial/complete proximal hamstring avulsion	Surgical	96	—	—	34				X
Bowman (2013)²⁰	10 (16)	Partial proximal hamstring avulsion	Surgical	17	—	—	32				X
Chahal (2012)²³	9 (16)	Complete proximal hamstring avulsion	Surgical	13	—	—	24	X			X
Hofmann (2014)⁴²	9 (16)	Complete proximal hamstring avulsion	Nonoperative	17	—	—	31	X			X
Klingele (2002)⁴⁷	10 (16)	Complete proximal hamstring avulsion	Surgical	11	180 (range, 90-300)	—	34	X
Konan (2010)⁴⁸	12 (16)	Complete proximal hamstring avulsion	Surgical	10	175 (range, 126-455)	—	12	X		X
Lefevre (2013)⁵¹	18 (24)	Partial/complete proximal hamstring avulsion	Surgical	34	171 ± 48	—	27	X		X	X
Léger-St-Jean (2019)⁵²	12 (16)	Complete proximal hamstring avulsion	Surgical	22	120 (IQR, 60-240)	—	6				X
Lempainen (2006)⁵⁴	10 (16)	Partial proximal hamstring avulsion	Surgical	48	150 (range, 30-360)	—	36
Piposar (2017)⁶²	18 (24)	Partial/complete proximal hamstring avulsion	(1) Surgical(2) Nonoperative	1510	—	—	3035	X			X
Sandmann (2016)⁶⁸	11 (16)	Complete proximal hamstring avulsion	Surgical	16	180 (range, 120-270)	—	56	X	X		X
Shambaugh (2017)⁷²	17 (24)	Complete proximal hamstring avulsion	(1) Surgical(2) Nonoperative	1411	—	—	4330	X			X
Skaara (2013)⁷⁷	9 (16)	Partial proximal hamstring avulsion	Surgical	31	—	—	30	X		X	X
Subbu (2014)⁸¹	12 (16)	Complete proximal hamstring avulsion	Surgical	78	112 (range, 84-224)	0.0	24
Willinger (2020)⁸⁷	11 (16)	Partial/complete proximal hamstring avulsion	Surgical	71	—	—	56				X

			Assessment
Lead Author (Year)	Risk of Bias ^b	N	Clinical	MRI
A Hamid (2014)¹	Low	28	X
A Hamid (2013)²	10 (16)	360	X
Askling (2006)⁵	12 (16)	33	X
Askling (2007)⁶	14 (16)	15	X	X
Askling (2007)⁷	14 (16)	18	X	X
Askling (2008)⁸	11 (16)	30	X	X
Askling (2014)⁹	Some concerns	56	X	X
Askling (2013)¹⁰	Some concerns	75	X	X
Cohen (2011)²⁴	14 (16)	38		X
Comin (2013)²⁵	20 (24)	62		X
Crema (2018)²⁷	11 (16)	22		X
Ekstrand (2012)²⁹	12 (16)	207		X
Ekstrand (2016)³⁰	12 (16)	255		X
Gibbs (2004)³³	12 (16)	31		X
Guillodo (2014)³⁶	12 (16)	128	X
Hallen (2014)³⁷	13 (16)	386		X
Hamilton (2018)⁴⁰	13 (16)	110		X
Jacobsen (2016)⁴⁴	14 (16)	90	X	X
Kilcoyne (2011)⁴⁵	10 (16)	48	X
Malliaropoulos (2010)⁵⁵	21 (24)	165	X
Moen (2014)⁵⁹	13 (16)	74	X	X
Pollock (2016)⁶³	11 (16)	44		X
Pomeranz (1993)⁶⁴	10 (16)	14		X
Schneider-Kolsky (2006)⁶⁹	21 (24)	58	X	X
Silder (2013)⁷⁶	Low	25		X
Slavotinek (2002)⁷⁵	12 (16)	30		X
van der Made (2018)⁸⁰	14 (16)	70		X
Verrall (2003)⁸¹	12 (16)	83	X	X
Wangensteen (2015)⁸²	11 (16)	180	X	X
Warren (2010)⁸³	13 (16)	59	X

Evidence-Based Management and Factors Associated With Return to Play After Acute Hamstring Injury in Athletes: A Systematic Review

Abstract

Background:

Purpose:

Study Design:

Methods:

Results:

Conclusion:

Keywords

Methods

Research Framework

Eligibility Criteria

Information Sources and Search

Study Selection

Data Collection

Risk-of-Bias and Quality Assessment

Statistical Analysis

Results

Study Selection

Study Characteristics

Risk-of-Bias Assessment

Synthesis of Results

Patient Characteristics

Management

Proximal Injuries

Muscular Injuries

Prognostic Factors

Clinical Factors

MRI Factors

Discussion

Conclusion

Footnotes

Notes

APPENDIX

References