Abstract
Background:
The Major League Baseball (MLB) Health and Injury Tracking System (HITS), created in 2010 with the MLB Players Association, was designed to overcome limitations of injured list-based reporting. It serves as a longitudinal injury surveillance platform and electronic medical record across major and minor league players.
Purpose:
To evaluate all publications related to the HITS database to provide an overview of epidemiology, treatment outcomes, and return-to-play (RTP) rates in professional baseball, guiding player safety and performance strategies.
Study Design:
Scoping review; Level of evidence, 4.
Methods:
All peer-reviewed publications utilizing the HITS database (2010-2023) were reviewed under PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Studies reporting epidemiology, surgical versus nonoperative management, and RTP outcomes across upper extremity, lower extremity, spine, and other injuries were synthesized.
Results:
From 2011 to 2016, HITS recorded 49,955 injuries, resulting in 722,176 missed days of play. Pitchers accounted for 39% of injuries, with the upper extremity most affected (39%). Ulnar collateral ligament (UCL) injuries, while the sixth most common, represented the leading cause of surgery (46%) and season-ending injuries (60%). RTP following UCL reconstruction ranged from 73% to 84%, though outcomes declined with revision procedures. Shoulder injuries were also prevalent: labral repairs showed moderate RTP rates (74%-82%), whereas rotator cuff repair yielded poor outcomes (14%-42%), leading to preference for nonoperative care. Lower extremity injuries included hamstring strains, hip/groin injuries, and meniscal pathology, with variable RTP timelines. Core injuries, lumbar spine disorders, and concussions also contributed significantly to time lost. Overall, HITS has informed >40 publications, highlighting variable outcomes by injury type, treatment, and player position.
Conclusion:
The HITS database provides the most comprehensive epidemiologic resource on injuries in professional baseball, identifying high-risk conditions and characterizing management outcomes. RTP success varies widely, with certain injuries such as UCL reconstruction yielding relatively favorable results, while others such as rotator cuff repair remain challenging.
Keywords
History and Goals of the MLB HITS Database
The Major League Baseball (MLB) Health and Injury Tracking System (HITS) was developed in 2010 in a collaboration between the MLB and the MLB Players Association to address deficiencies in prior injury monitoring practices, which historically relied on the injured list and were limited by incomplete reporting and nonmedical roster management decisions. HITS functions as a longitudinal electronic medical record and injury surveillance platform, uniquely capturing data from all players across both major and minor league affiliates. Its primary objective is to efficiently track player medical histories throughout their careers, while secondary aims include identifying injury patterns, monitoring areas of concern, and facilitating epidemiologic research to inform strategies for improving player health and safety through potential rule changes, equipment modifications, and educational initiatives.
Scope of Data Collection
The MLB HITS database collects data documenting any injury or physical impairment sustained by a player that results in restricted participation or functional limitation in any baseball-related activity. This includes off-field activity such as weight training and conditioning, as well as on-field activity such as warm-up, practice, and playing in a game. These injuries are further categorized by the timing of the injury—off season, spring training, regular season, or postseason (Table 1). Importantly, because the minor league system contains a far larger population of players than the major leagues, the total number of injuries recorded in HITS is typically higher among Minor League Baseball (MiLB) players. The HITS database has a unique identifying number for each player, which allows the injury information to be linked to demographic data, personnel records, and performance metrics (Table 2).
Summary of Variables Collected in the Health and Injuring Tracking System (HITS) database
Summary of Performance Metrics in Major League Baseball5
Summative Report on Time Out of Play for MLB and MiLB Injuries
Camp et al 5 conducted a summative report on all MLB and MiLB injuries from 2011 through 2016 using the HITS database. Throughout the study period, a total of 49,955 injuries were recorded. Of these, 45,123 were non–season ending injuries, collectively accounting for 722,176 days of missed play. Pitchers were affected in 39.1% of all cases. Upper extremity injuries represented 39% of the total, while 35% involved the hip, groin, or lower extremity. Surgical intervention was necessary in 6.5% of injuries, and 9.7% ultimately resulted in a season-ending outcome. 5 This summative report eloquently highlighted the most common injuries in professional baseball players up until 2016. The purpose of this narrative review was to evaluate all publications related to the HITS database to provide overview of epidemiology, treatment outcomes, and return-to-play (RTP) rates in professional baseball, guiding player safety and performance strategies. By doing so, we aimed to update several of the key findings in the prior summative report, while also highlighting the advancements being made through the HITS database.
This article serves to expand and update the injuries tracked in the HITS database, while also highlighting the findings from this summative report (Table 3).
MiLB, Minor League Baseball; MLB, Major League Baseball.
Methods
Search Strategy
In August 2024, a systematic review of the PubMed database was completed based on the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. The following search terms were used: ((Major League Baseball Health and Injury Tracking System) OR (MLB HITS) OR (Major League Baseball)). Papers were included if they used the MLB HITS database to describe an injury in professional baseball players. All resulting studies were screened by 2 independent researchers (B.A.L. and B.J.E.) with the aforementioned criteria. (Figure 1) The senior author (A.A.R.) was consulted to arbitrate any disagreements that arose.
PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) diagram for screening studies for inclusion and exclusion. HITS, Health and Injury Tracking System; MLB, Major League Baseball.
Results
Upper Extremity Injuries
Shoulder Injuries
The shoulder and clavicular region represents the most commonly injured body region among professional baseball players. 5 The MLB HITS database contains several studies focused on shoulder pathology in professional baseball players.5,6,8,20,33-35 Chalmers et al 6 evaluated all shoulder surgeries in MLB players between 2012 and 2016, reporting 581 surgical procedures across 542 professional players (60 pitchers) with an overall incidence of 1.48%. The most common procedures involved the glenoid labrum (61%), rotator cuff (32%), and subacromial space (24%), with return to prior level of play rates of 45% in pitchers and 38% for position players.
Labral tears, including superior labrum anterior to posterior (SLAP) lesions, are particularly common among throwing athletes. Several HITS-based studies have evaluated outcomes following labral repair.33-35 Paul et al 34 examined 53 professional baseball players who underwent SLAP repair—36 pitchers and 17 position players—reporting an RTP rate of 82% for pitchers and 81% for position players without significant changes to their performance metrics. The authors did not report the RTP rate at the same level or higher in this study. A separate study by Paul et al 35 on isolated posterior labral repair—78 pitchers and 55 position players—found a lower rate of RTP for pitchers at 74.5% versus position players at 91% following isolated posterior labral repair—the authors did not report on RTP at the same level or higher in this study.
Rotator cuff injuries also contribute significantly to shoulder pathology in baseball players. Erickson et al 20 investigated performance and RTP following rotator cuff surgery in 151 professional baseball players—61% pitchers—finding that nonoperative management was preferred because of poor surgical outcomes. Among players undergoing surgery, RTP rates at the same level were 42.3% following debridement and only 14.3% following rotator cuff repair, with notable declines in performance metrics.
Internal impingement represents another cause of shoulder dysfunction, particularly in pitchers. Chalmers et al 8 evaluated 624 professional pitchers over 6 years and found that cumulative workload (innings pitched) and starting pitcher status, but not acute workload increases, were significantly associated with internal impingement risk.
Last, Marigi et al 33 reported on shoulder injuries among professional batters, identifying rotator cuff injuries (23.1%), subacromial impingement/bursitis (14.4%), and contusions (14.0%) as the most common diagnoses. Despite excluding pitchers, throwing remained the leading mechanism of injury. SLAP tears had the highest surgery rate (45.1%) and season-ending injury rate (35.3%), followed by anterior instability with labral tear.
Acromioclavicular Joint Injuries
Acromioclavicular joint injuries are relatively uncommon in overhead athletes. Frantz et al, 24 using the MLB HITS database, identified 312 AC joint injuries over a 6-year period, most frequently affecting outfielders (34.6%), infielders (26.6%), and starting pitchers (7.1%). Contact during fielding was the predominant mechanism. Most injuries were managed nonoperatively, with only 5.4% requiring surgery. Surgically treated players missed a mean of 219.4 days compared with 20.7 days in the nonsurgical group. All players returned to sport, although return to the same or higher level was not reported. 24
Thoracic Outlet Syndrome
Thoracic outlet syndrome (TOS) is an uncommon but recognized source of upper extremity dysfunction in professional baseball players. Chauhan et al, 9 using the HITS database, performed a matched cohort analysis of 52 players who underwent TOS surgery between 2010 and 2017. Of these, 88% were pitchers, with neurogenic TOS (69%) more common than venous TOS (29%). The RTP rate at the same or higher level was 70% at a mean of 9.5 months postoperatively, with no significant differences between MLB and MiLB players. 9
Chest and Upper Back Injuries—Pectoralis Major, Latissimus Dorsi, and Teres Major Injuries
Chest and upper back injuries are less common than shoulder and upper extremity injuries in professional baseball players. Haeberle et al, 27 using the HITS database, identified 138 pectoralis muscle injuries between 2011 and 2017, primarily strains (n = 133) rather than tears or ruptures (n = 5), most often occurring during pitching (45.9%), throwing (28.6%), or weightlifting. Only 2.9% required surgery, and all players returned to play after a mean of 19.5 days, although return to the same or higher level was not reported. No subanalysis comparing operative and nonoperative treatment was performed, and several players with partial tears returned without missed time, lowering the overall mean despite inclusion of surgical cases.
Latissimus dorsi and teres major (LD/TM) injuries have become a more commonly recognized source of pain and disability among professional baseball players, specifically pitchers. Erickson et al 18 investigated performance and RTP after LD/TM tears among professional baseball pitchers between 2011 and 2016—including 120 pitchers, 42 were MLB players (35%) the rest were MiLB players. Most were treated nonoperatively (89.2%), with a 75% RTP rate at the same or higher level. Operatively treated players missed more time (406 ± 146 days vs 170 ± 169 days) but maintained performance levels, while nonoperative players experienced declines.
Ulnar Collateral Ligament (UCL) Injuries—Primary UCL Injuries
UCL injuries are one of the most frequently discussed injuries in professional baseball players with an increasing incidence over the past 2 decades. UCL injuries rank as the sixth most common injury in professional baseball, but account for the highest percentage of injuries requiring surgery (46.3%) and the highest percentage of season-ending injuries (60%). 5
The first UCL HITS database publication by Erickson et al 13 examined retirement following UCL reconstruction (UCLR) in MLB pitchers using the HITS database as a cross-reference source. Among 153 retired pitchers post-UCLR, the mean time to retirement was 4.4 ± 3.5 years, similar to controls without UCLR (4.4 ± 4.7 years). Pitchers undergoing UCLR were more likely to be released during the season, although shoulder or elbow injuries were not more common causes of retirement compared with controls. Decline in performance was the leading cause of retirement post-UCLR.
In 2018, Camp et al 3 conducted an epidemiologic study of UCLR in MMLB and MiLB players using the HITS database as a cross-reference source. The final cohort included 1429 UCLRs. The authors reported that 83.7% of players returned to any level of play at a mean of 435 days, whereas 72.8% returned to their prior level of play at a mean 506 days. MLB players were more likely to RTP and to their prior level of performance than minor leaguers. The overall revision rate was higher in MLB players (6.7%) compared with minor leaguers (5.2%).
In 2019, Erickson et al 16 compared outcomes after UCLR using hamstring versus palmaris autograft in 195 players. RTP rates at the same or higher level were similar (61% hamstring vs 68.7% palmaris), with both groups demonstrating postoperative declines in performance metrics (wins above replacement, walks plus hits per inning pitched). Players with hamstring grafts sustained more contralateral lower extremity injuries, while palmaris graft recipients had a higher, though not statistically significant, rate of upper extremity injuries.
In 2019, Chauhan et al 10 investigated the nonoperative treatment of UCL injuries with and without platelet-rich plasma (PRP) in professional baseball players using the HITS database. The study included 544 professional baseball players—133 who received PRP injections and 411 who did not prior to their nonoperative treatment program. These players were matched by age, position, throwing side, and MLB versus MiLB status. Overall, nonoperative treatment of UCL injuries in this study yielded a 54% RTP rate. Players treated with PRP experienced significantly longer delays in both return to throwing and overall RTP. In matched-cohort analysis, pitchers who did not receive PRP—particularly those in MiLB—returned to throwing and competition more quickly. However, long-term outcomes did not differ significantly between groups on survival analysis.
Finally, in 2020, Erickson et al 23 reported on the timing of return to batting milestones following UCLR in professional baseball players using the HITS database. The most common positions were catchers and shortstops, while 76% of players had UCLR on the trail/back arm while batting. Of the 137 players included, 71% were able to RTP at the same or higher level. Overall hitting utilization—at bats and hits—decreased following UCLR in batters.
UCL Injuries—Revision UCL Injuries
Given the increasing number of primary UCLRs being performed, the number of revision UCLRs is also increasing.4,14 Camp et al 4 investigated revision UCLR in professional baseball players from 2010 to 2016 using the HITS database. The authors reported on 69 professional baseball pitchers who underwent revision UCLR at a mean of 47 months after their primary UCLR. The most commonly used revision UCLR tunnel configuration was the modified Jobe figure-of-8 technique (59.4%) followed by the docking technique (24.6%), and the most commonly used graft was hamstring autograft (49.3%), followed by palmaris longus autograft (31.9%). In terms of RTP, 76.6% pitchers achieved RTP, but only 55.3% were able to return to the same level at a mean time of 14.5 months.
Erickson et al 14 more recently investigated revision UCLRs from 2010 to 2023 in professional baseball players using the HITS database. Overall, 191 pitchers were included in the study—130 MiLB players (68%)—with revision surgery occurring at a mean of 45 months after index procedure. The authors reported the most commonly used graft source to be the hamstring tendon autograft (47%) as was seen in the Camp et al 4 study, followed by palmaris longus autograft (35%). 14 Conversely, however, the tunnel configuration was found to be equal in occurrence between the modified Jobe technique and the docking techniques (37% each). 14 The RTP at any level rate was found to be slightly lower at 72% at a mean of 18 months, however, only 58% were able to return to the same level of play at a mean 20 months. 14
Flexor–Pronator Mass Injuries
The flexor–pronator mass serves as a secondary dynamic stabilizer against valgus stress in throwing athletes. Hodgins et al, 28 using the HITS database, identified 763 forearm flexor injuries between 2010 and 2014, predominantly in minor league players (82%). Mean time missed was 117 days in MLB and 93.9 days in MiLB. Pitchers showed a decline in performance metrics across all categories leading up to the season in which they sustained a flexor pronator injury. Following a flexor-pronator injury, there was an increased incidence of subsequent upper extremity injuries—including those to the shoulder, elbow (including UCL), and forearm. As such, flexor-pronator injuries should be recognized as a significant risk factor for future upper extremity pathology, particularly UCL injuries.
Elbow Fractures—Olecranon Fracture, Medial Epicondylar Fracture
Fractures of the elbow are uncommon in professional baseball players; however, when they occur, they can be a cause of significant morbidity. Erickson et al, 15 using the HITS database (2010-2016), reported on 52 players undergoing open reduction and internal fixation (ORIF) for olecranon fractures, the majority of which were stress fractures (73.1%). 15 RTP rates at the same or higher level were 57.9% for stress fractures and 83.3% for acute fractures, with a mean return time of 314 ± 206 days.
Medial epicondylar fractures, often occurring as a complication after UCLR, are another uncommon elbow injury. Erickson et al 17 evaluated 15 pitchers who underwent ORIF between 2010 and 2016, finding an RTP rate of 73.3%, although only 55% returned at the same or higher level.
Ulnar Nerve Neuropathy
Ulnar neuropathy, or cubital tunnel syndrome, is an uncommon but significant issue in professional baseball players and may occur independently or following UCLR. Erickson et al, 19 using the HITS database (2010-2016), reviewed 52 players (83% pitchers), 14 of whom had prior UCLR. A total of 62% returned to sport after isolated ulnar nerve decompression or transposition, with 56% returning at the same or higher level.
Hand/Wrist Injuries
Although less common than other upper extremity injuries, professional baseball players are at increased risk for both acute and chronic hand and wrist injuries. Rhee et al, 36 using the HITS database (2011-2016), reported 4478 hand injuries and 1748 wrist injuries, with the most common diagnoses being hand contusion (42.4%), wrist sprain (33.7%), wrist contusion (25.3%), hook of hamate fracture (10.6%), thumb UCL rupture (7.4%), and metacarpal fracture (4.7%). Hook of hamate (72%) and scaphoid fractures (60%) most frequently required surgery. Chalmers et al 7 separately evaluated outcomes after hook of hamate excision in 261 players—96% hitters, 89% acute fractures, and 11% nonunions. The RTP rate at the same or higher level was high at 81% at a mean of 48 days after surgery.
Lower Extremity Injuries
Hip and Groin Injuries
Hip and groin injuries in professional baseball players include muscle strains, avulsions, contusions, and femoroacetabular impingement (FAI) syndrome. Coleman et al, 11 using the HITS database (2011-2014), reported 1823 hip or groin injuries, 95% of which were extra-articular, most commonly adductor strains (40.8%) and iliopsoas strains (21.2%). Intra-articular pathology was less frequent, with FAI (2.2%) and labral tears (1.5%) being the most common; these injuries more often required surgery and resulted in a mean of 123 days missed.
Hamstring Injuries
Hamstring strains are the most common injury among professional baseball players, 5 often occurring through noncontact mechanisms such as base running, fielding, and pitching. Ahmad et al, 1 using the HITS database from 2011, identified 286 hamstring strains, with a mean of 24 days missed in MLB and 27 days in MiLB players, most frequently during baserunning to first base. Chalmers et al 7 later reported 1042 hamstring strains between 2011 and 2017, predominantly in position players (97.8%), with increased risk associated with shorter rest intervals, greater defensive innings, and higher plate appearances.
Knee Injuries (Ligamentous, Meniscal)
Knee injuries are less common in professional baseball compared with other sports such as basketball or football. Dahm et al, 12 using the HITS database (2011-2014), reported 2171 knee injuries, most commonly in baserunners (24%) and primarily from noncontact mechanisms (44%). Overall, 12.6% required surgery. The most frequent diagnoses were knee contusion (30.5%), patellar tendinopathy (10.2%), medial collateral ligament sprain (5.5%), medial meniscal tear (4.7%), lateral meniscal tear (4.5%), and lateral collateral ligament sprain (2.1%).
Erickson et al21,22 evaluated outcomes following meniscectomy 22 and meniscal repair 21 in professional baseball players using the HITS database (2010-2017). Among 168 players undergoing meniscectomy, RTP was 80% overall and 76% at the same or higher level, compared with 68% for 31 players undergoing meniscal repair. Most repairs were all-inside (60%), with mean time missed significantly longer for meniscal repair (209 days) than meniscectomy (42 days).
Gastrocnemius Injuries
Gastrocnemius injuries are a common lower extremity issue in professional baseball players. Hultman et al, 29 using the HITS database (2011-2016), identified 402 injuries, most frequently during baserunning (36.1%) and fielding (23.6%). The most common diagnoses were gastrocnemius strain (64.2%), spasm (35.1%), and tear (0.7%), with MLB players missing a mean of 12.7 days and MiLB players 10.9 days. All players returned to sport. Chalmers et al 7 further found that position players with shorter rest intervals, more innings, and more plate appearances were at increased risk for calf injury.
Ankle/Foot Injuries
Ankle and foot injuries are common in sports, and professional baseball players experience these injuries as well. Lucasti et al 30 investigated all ankle and lower leg injuries in professional baseball players using the HITS database between 2011 and 2017. Over the study period, there were 4756 ankle and lower leg injuries, most commonly ankle sprain (37%), followed by leg contusion (24.5%) and muscle strain (12.7%). A total of 127 of these injuries (2.7%) required surgery, most commonly for fibular fracture (20.4%), followed by ligamentous ankle injury (15.7%) and various other causes, such as tibial stress fracture (3.9%) and Achilles tendinopathy (3.9%). The mean number of days missed regardless of surgery was 27.8 days.
Other Injuries
Abdominal Oblique Injuries
Abdominal oblique injuries are the fifth most common injury in professional baseball players, given the core's critical role in swinging, throwing, and running. 20 Camp et al, 2 using the HITS database (2011-2015), identified 996 oblique injuries, with 26% in MLB and 74% in MiLB players. Batting (46%) and pitching (35%) were the most common mechanisms, typically involving the lead side (77%). Most injuries were treated conservatively; however, players receiving corticosteroid or PRP injections experienced 11 days longer recovery. Recurrence occurred in 7.4% of cases at a mean of 428 days.
Spinal Injuries
Lumbar spinal conditions are a common source of lower back pain in professional baseball players, with paralumbar strains being the third most frequent injury.5,31 Makhni et al, 31 using the HITS database (2011-2017), identified 206 lumbar spine injuries, most commonly lumbar disc herniation (41.7%), pars stress fracture/reaction (23.7%), and disc degeneration (22.3%). 5 Surgical intervention was required in 13.1% of cases, with 25% of surgeries resulting in season-ending injuries. Total days missed averaged 4134 for MiLB players and 1814 for MLB players.
Makhni et al 32 also reviewed 172 spine-related neurologic injuries between 2011 and 2016, with 73.3% involving the lumbar spine and 26.7% the cervical spine. Surgical intervention was more common in lumbar injuries (18.3%) than cervical (13%), and lumbar conditions accounted for a greater total time lost (3380 vs 866 days).
Concussions
Sports-related concussions, or mild traumatic brain injuries (MTBIs), are an increasing concern in professional baseball. Green et al, 26 using the HITS database (2011-2012), reported 307 MTBIs (41 in MLB, 266 in MiLB), accounting for 1% of injuries resulting in time lost. A standardized RTP protocol was required, with a mean of 9 days missed per injury.
Green et al 25 further analyzed batting performance following MTBI in MLB position players (2011-2015), identifying 77 MTBI events with a mean of 11.4 days missed. No significant differences in batting performance were observed when comparing metrics 30 and 60 days before injury.
Fractures
While MLB lacks the high-impact collisions often seen in contact sports such as football or hockey, fractures still account for a notable share of injuries in professional baseball players. Rubenstein et al 37 used the HITS database to explore the epidemiology of fractures in professional baseball from 2011 to 2017. During the study period, there were a total of 1798 fractures—342 in MLB players and 1456 in MiLB players. The most common fractures were hand/finger/thumb (32.6%), followed by wrist (17.5%) and head/face (10.4%). The mean time missed due to fracture was 56.6 ± 48.4 days. The most common mechanism was contact with the ball (46.1%) during batting (43.9%); however, the most common position to sustain a fracture was starting pitchers (12.6%).
Discussion
The major findings of this review demonstrated that injury outcomes in professional baseball vary substantially by anatomic region, injury subtype, and positional demands, with the throwing shoulder and elbow presenting the greatest challenges to return to prior performance. Shoulder injuries remain particularly problematic, as fewer than half of players regain preinjury levels despite moderate overall RTP rates, reflecting the shoulder's complex, individualized biomechanics and the “all-or-nothing” return pattern observed in pitchers. In contrast, UCLR reliably enables RTP for most athletes—especially MLB pitchers—though performance decline is common, nonoperative management of partial tears is inconsistent, and revision surgery carries a markedly worse prognosis; flexor-pronator injuries further serve as an important warning sign for future elbow pathology. Other upper extremity injuries generally demonstrate more favorable outcomes, though conditions involving the elbow, ulnar nerve, or key throwing musculature (latissimus dorsi/teres major) require prolonged rehabilitation and careful management. Lower extremity injuries account for a large proportion of overall injury burden and missed time, with muscle strains being most common but typically recoverable, while intra-articular hip and surgically treated knee or ankle injuries result in longer absences despite high eventual return rates. Finally, trunk, spinal, concussion-related, and fracture injuries—though less frequent—collectively impose significant time loss due to baseball's rotational demands and ball-impact mechanisms. Taken together, these findings emphasize that while many professional baseball injuries permit RTP, return to prior performance is far from guaranteed, underscoring the need for sport-specific prevention, individualized treatment strategies, and realistic counseling regarding prognosis and career impact.
Shoulder Injuries
Shoulder injuries remain among the most challenging conditions in professional baseball, with labral tears, rotator cuff pathology, and subacromial impingement comprising the majority of cases. Data from the MLB HITS database consistently show that although approximately 60% to 70% of players return to some level of play following shoulder surgery, fewer than half regain their prior level. This disparity reflects the uniquely complex biomechanical demands of the shoulder as well in combination with high-level throwing.
Unlike the elbow—whose primary task during pitching is to resist valgus stress—the shoulder must accommodate multiplanar motion and tolerate adaptive biomechanical changes that would be considered pathologic in nonthrowers. Elite pitchers often develop supraphysiologic external rotation and increased humeral head translation, adaptations that enhance velocity but also place the joint near the limits of stability. These adaptations vary markedly between athletes; as a result, distinguishing beneficial laxity from true pathology is inherently difficult. The same degree of capsular laxity may be normal for one pitcher yet injurious for another, complicating both diagnosis and postoperative expectations. This study's findings reinforce that the shoulder's more intricate mechanics contribute significantly to the difficulty pitchers face when attempting to RTP after surgery.
These biomechanical realities help explain observed RTP patterns. Pitchers, who experience the highest cumulative shoulder stress, have lower overall RTP rates but, when they do return, are more likely to regain preinjury performance—creating an all-or-nothing phenomenon. Position players, by contrast, can often return in reduced throwing roles or at less demanding defensive positions, which elevates overall RTP rates but yields fewer full returns to form. Injury subtype further modifies prognosis: SLAP and posterior labral repairs show relatively favorable outcomes, while rotator cuff surgery—especially full-thickness repairs—demonstrates poor return rates and frequently ends careers.
These findings underscore critical clinical implications. Prevention and workload management remain essential, particularly for pitchers, given the strong correlation between cumulative innings and overuse mechanisms such as internal impingement. Nonoperative treatment should be prioritized for many rotator cuff and select labral injuries, especially in older athletes and those nearing career endpoints. When surgery is necessary, players should be counseled that return to prior performance is uncertain and may require 9 to 12+ months of rehabilitation. Postoperative plans should be individualized according to positional demands—gradual interval throwing programs for pitchers and temporary positional modifications for field players—to ensure controlled reloading of the healing shoulder.
Ultimately, while a subset of athletes can successfully return to elite play, persistently low return-to-prior-level rates highlight the need for continued innovation in surgical techniques, biologic augmentation, and rehabilitation strategies tailored to the unique, highly individualized mechanics of the throwing shoulder.
UCL Injuries and Flexor-Pronator Injuries
UCL injuries have increased sharply in professional baseball and, while only about the sixth most common injury type, they account for a disproportionate share of surgeries and season-ending injuries. UCLR generally permits RTP, with large HITS-based series showing overall RTP rates above 80% and roughly 70% to 75% of players returning to their prior level, particularly among MLB pitchers. Career length after UCLR appears similar to controls, though post-UCLR pitchers are more likely to be released midseason and many ultimately retire for performance-related reasons. Graft choice (palmaris vs hamstring) does not meaningfully alter RTS rates or timing, although each may be associated with different subsequent injury patterns, and most pitchers experience some decline in advanced performance metrics after surgery. Nonoperative management for partial UCL tears succeeds in only about half of professional players, and adjunctive PRP has not convincingly improved RTP rates or timelines. Outcomes for position players are also generally favorable, but recovery of full offensive workload and preinjury usage is less predictable. Revision UCLR is increasingly common and carries a markedly worse prognosis: only about 70% to 75% return to any professional level and barely half regain their prior level, often after 14 to 20 months of rehabilitation.
Flexor–pronator mass injuries add an important layer to this picture as both a major source of downtime and a harbinger of future elbow pathology. Forearm flexor-pronator strains in pitchers are associated with significant time lost (3-4 months on average) and precede elevated rates of subsequent shoulder, elbow, and especially UCL injuries, with a notable proportion of these athletes ultimately undergoing UCLR. Performance metrics often deteriorate in the season leading up to a flexor injury, suggesting underlying fatigue or biomechanical compromise. Consequently, flexor-pronator injuries should be viewed as a red flag that prompts careful evaluation of the UCL, thoughtful workload modification, and targeted strengthening of the forearm musculature. For sports medicine surgeons, these data underscore the need for early recognition of medial elbow and forearm symptoms, individualized return-to-throw programs, and integrated prevention strategies aimed at protecting both the dynamic and the static stabilizers of the elbow.
Other Upper Extremity Injuries
Across the upper extremity, injuries outside the shoulder remain important but generally less frequent in professional baseball players, with wide variability in recovery depending on injury type and treatment. Acromioclavicular joint injuries most often occur from contact during fielding and are usually treated nonoperatively, allowing return within weeks; surgery is rare and associated with prolonged recovery. Thoracic outlet syndrome, though uncommon, affects primarily pitchers and often necessitates surgery, with approximately 70% successfully returning to their prior level after nearly a year of rehabilitation. Chest and upper back musculature injuries show similarly varied outcomes: most pectoralis major strains resolve quickly with conservative management, while latissimus dorsi and teres major injuries—particularly impactful for pitchers—demonstrate good RTP rates overall, though operative cases require far longer recovery times.
Elbow fractures and nerve-related injuries, while less common, pose substantial challenges. Olecranon and medial epicondylar fractures treated surgically yield moderate RTP rates, with acute fractures faring better than stress injuries. Ulnar nerve neuropathy is another meaningful source of lost playing time, especially in pitchers and those with prior UCLR, with only about half returning to their previous performance level after decompression or transposition. In contrast, hand and wrist injuries are common but often less debilitating; although many require surgical management—particularly hook of hamate or scaphoid fractures—players generally return quickly and at high rates. Together, these studies highlight that while many nonshoulder upper extremity injuries in baseball have favorable outcomes, those involving the elbow or throwing musculature carry a more guarded prognosis, emphasizing the need for early recognition, tailored treatment, and sport-specific rehabilitation strategies.
Lower Extremity Injuries
Lower extremity injuries represent a major share of musculoskeletal problems in professional baseball and have a substantial impact on player availability. Hamstring strains are the most common injury in the sport, with >2600 cases recorded from 2011 to 2016 and an incidence that continues to rise. Knee injuries account for roughly 6% to 7% of all cases, while ankle and foot injuries make up 10% to 15%, and hip/groin injuries about 5%. Although many of these injuries—such as mild hamstring strains, calf strains, groin strains, and ankle sprains—are low grade and treated nonoperatively, their cumulative effect is significant, costing thousands of days of missed play. Intra-articular hip pathology and surgically treated ankle or knee injuries are less common but far more debilitating, often requiring months of recovery. Workload factors, especially limited rest days, have emerged as key contributors to muscle injury risk, emphasizing the need for balanced scheduling.
Despite the burden of these injuries, outcomes are generally favorable when conditions are correctly diagnosed and treated with sport-specific strategies. Hip arthroscopy for FAI or labral tears yields RTP rates of 80% to 90%, partial meniscectomy allows most players to return within 6 weeks, and nearly all athletes recover fully from mild-to-moderate muscle strains. Across the league, both MLB and MiLB, prevention efforts continue to evolve, integrating eccentric strengthening, flexibility work, proprioceptive training, and analytics-driven workload monitoring. For sports medicine surgeons, understanding baseball-specific biomechanics and position-based demands is essential for tailoring treatment and RTP timelines. By combining injury surveillance data with individualized rehabilitation and strategic rest planning, teams can reduce recurrence rates and minimize time lost, ensuring athletes maintain peak performance throughout the season.
Other Injuries
Abdominal oblique and lumbar spinal injuries represent major sources of lost playing time in professional baseball due to the high rotational and torsional demands of batting and pitching. Oblique strains rank among the top 5 most common injuries, with nearly 1000 cases identified from 2011 to 2015 and most occurring during batting or pitching on the lead side of the torso. These injuries are typically treated conservatively, though injections were associated with longer recovery, and recurrence occurs in ~7% to 8% of players more than a year after RTP. Lower back injuries are similarly impactful: lumbar disc herniations, pars stress injuries, and degenerative conditions collectively caused nearly 6000 missed days across 6 seasons, with 13% requiring surgery and nearly one-third being season ending. Pitchers are disproportionately affected because of repetitive rotational loading. Neurologic spine injuries further compound this burden, with lumbar conditions leading to longer absences than cervical injuries and totaling over 4200 missed days in a 5-year period.
Although concussions account for only about 1% of all injuries, they remain a high-priority concern because of their potential neurologic implications; most players miss about 9 to 11 days, but position players generally return without measurable short-term declines in batting performance. Fractures, while less common than soft tissue injuries, still produced nearly 1800 cases from 2011 to 2017 and typically resulted from direct ball impact, particularly during batting or on the mound. Hand and wrist fractures were most common, and pitchers constituted the single largest positional group affected, often from line-drive comebackers. These data underscore that despite baseball's noncontact nature, trunk, spinal, head, and bone injuries collectively impose a substantial burden, emphasizing the importance of refined prevention strategies, protective equipment, and evidence-based RTP protocols.
Limitations and Strengths of the HITS Database
The MLB HITS provides an unprecedented, leaguewide surveillance platform that captures all injuries and medical events across major and minor league players, enabling population-level analysis, rich clinical detail through integration with the electronic medical record, and deterministic linkage to workload metrics, outcomes, and costs. Its comprehensive structure supports sophisticated longitudinal research, prospective surveillance, and policy evaluation—already contributing to changes such as the 7-day concussion injured list. However, HITS also has limitations, including reliance on athletic trainers’ manual data entry, early issues with missing or inconsistent data, and imprecise exposure measurement given that athlete exposures do not reflect true workload and practices are not captured. Research definitions further exclude non–time loss and offseason injuries, potentially missing important precursor conditions. Variability in coding practices, risk of misclassification, and restricted access centralized through the Johns Hopkins research team also constrain analytic flexibility. Despite these limitations, HITS remains the most robust injury surveillance system in professional baseball and continues to evolve to improve data quality and exposure assessment.
Conclusion
The HITS database provides the most comprehensive epidemiologic resource on injuries in professional baseball, identifying high-risk conditions and characterizing management outcomes. RTP success varies widely, with certain injuries such as UCLR yielding relatively favorable results, while others such as rotator cuff repair remain challenging. The MLB HITS database enables evidence-based decision-making and supports injury prevention, safety policy, and management strategies to optimize health and career longevity of professional baseball players.
Footnotes
Final revision submitted December 21, 2025; accepted January 4, 2026.
The authors have declared that there are no conflicts of interest in the authorship and publication of this contribution. 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.
