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Abstract

Objective

Arthroscopic partial meniscectomy (APM) is one of the most commonly performed surgical procedures. However, the indications for APM are controversial and obese patients may have worse outcomes. This study’s primary purpose was to investigate differences in outcome after APM associated with elevated body mass index (BMI). Secondary objectives included differences in pathophysiology, surgical complications/failures, or osteoarthritis development.

Design

MEDLINE, EMBASE, and OVID databases were systematically searched for eligible studies reporting on APM outcomes at a minimum of 1 year postoperatively. Studies that did not include BMI categorization were excluded. Meta-analysis was conducted with random-effects modeling where data from at least 2 studies was available.

Results

A total of 16 articles were included. Overweight/obese BMI was associated with worse preoperative Lysholm (mean difference, −6.06 [95% CI, −11.70 to −0.42]) and visual analogue scale pain scores (0.43 [0.07 to 0.79]). Worse postoperative normalized knee-specific patient-reported outcome scores were also associated with obese BMI (−4.57 [−5.33 to −3.81]). There were no significant differences in clinical improvement or osteoarthritis progression among BMI groups. Two studies found higher complication/failure rates, 3 articles associated medial meniscus posterior root tears, and 1 article found differences in gene transcript expression with increased BMI.

Conclusions

Obesity is associated with worse knee function after APM, and patients with elevated BMI have worse preoperative knee pain and function. However, there is no difference in amount of improvement between elevated and normal BMI patients. Further prospective research is necessary to determine the comparative effectiveness of APM in patients with elevated BMI.

Keywords

knee meniscus tear meniscectomy obesity body mass index (BMI)

Introduction

In a 10-year span from 1996 to 2006, the number of arthroscopic knee procedures increased by 49%, and over half were performed for meniscal tears in just 1 year.¹ Arthroscopy for meniscal tears was also the single most commonly-reported procedure to the American Board of Orthopaedic Surgery from 1999 to 2003.² The specific surgical treatment of meniscal tears varies depending on multiple clinical and patient factors but when meniscal tears are symptomatic and irreparable, arthroscopic partial meniscectomy (APM) is currently the gold standard.³ However, obesity may affect surgical outcome and there is no consensus in the current literature on how body mass index (BMI) should factor into the clinical decision-making process for treatment of meniscal tears.

Almost 40% of the US population was obese in 2016, and this number is projected to continue increasing.^4-6 Patients with elevated BMI are thought to experience higher load through the knee joint, altered alignment and gait, and often have higher levels of pro-inflammatory cytokines associated with increased adipose tissue.^7,8 These characteristics may affect the pathoanatomy and/or pathophysiology of meniscal tears, and could contribute to the development or progression of knee osteoarthritis (OA). Meniscal tears and APM are independently associated with knee OA in previous literature, and obesity may further increase the risk of OA.^9-12 Additionally, increased BMI is associated with increased risk of postoperative complications such as venous thromboembolism or surgical site infections.^13,14 Therefore, it is critical for orthopedic surgeons to understand how obesity may play a role in treatment of meniscal tears with APM.

The purpose of this study is to investigate any differences in surgical outcomes associated with overweight and/or obese BMI after APM. Secondary goals of this study include assessing differences in postoperative complications or failures and in pathophysiology of meniscal tears among BMI classification groups.

Methods

This study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and was registered with PROSPERO.^15,16 Studies that reported mechanism of injury, pathoanatomy/pathophysiology, outcomes, and complications of partial meniscectomy in the overweight and obese patient population were eligible. Two authors (T.Z. and J.J.J) independently and systematically searched the MEDLINE, EMBASE, and OVID electronic libraries up to July 2019 for any articles that met the eligibility criteria by using the following Boolean string: menis*[ti] AND (obese OR overweight OR BMI OR “body mass index”). All articles were checked for references to identify any other articles that could potentially meet eligibility criteria.

Articles were then screened based on the following inclusion criteria: (1) primary partial meniscectomy; (2) skeletally mature; (3) containing comparison groups based on BMI category/classification; (4) minimum follow-up of 1-year postoperatively; (5) original article; (6) published in English; and (7) human study population. The exclusion criteria were the following: (1) bilateral or revision partial meniscectomy; (2) previous or concomitant meniscus repair or meniscus transplantation; (3) previous or concomitant ligamentous reconstruction; (4) lack of stratification by BMI; (5) studies that excluded any groups that would be considered overweight or obese by BMI; and (6) any publication that was a case report, review, abstract, or technical notes. The quality of the included studies was assessed based on the Methodological Index for Non-Randomized Studies (MINORS) criteria and any study with a MINORS score less than 16 was excluded.¹⁷ In order to guarantee full inclusion of the adequate studies this process was independently performed by both authors, if any discrepancies appeared, these were resolved by the senior author (R.F.H.).

The initial search returned 239 total articles, and 45 additional records were identified via cross-referencing relevant articles, for a total of 284 articles. Articles were excluded due to the listed exclusion criteria either during initial screening of abstracts or evaluation of full-text articles as seen in Figure 1 . There was a total of 16 studies that met all the criteria and were included in this study ( Table 1 ). Four of those articles used the same or overlapping patient cohorts but each produced different analyses such as tibiofemoral versus patellofemoral or radiographic versus symptomatic OA.^18-21

Figure 1.

PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) flow diagram of systematic literature search.

Table 1.

Detail of Included Articles.

Authors, Year	Level of Evidence	No. of Patients	No. of Obese patients	Follow-Up in Months, Mean (Range)		Patient Age in Years, Mean (±SD or Range)
Englund et al., 2003	III	155	19	193.2	NR	38.2	(±12)
Englund and Lohmander, 2004	III	317	38	216	NR	36	(±12)
Englund and Lohmander, 2005	III	317	38	216	NR	36	(±12)
Paradowski et al., 2005	III	143	16	NR	(168-192)	50	(27-83)
Ozkoc et al., 2008	III	67	13	56.7	(8-123)	55.8	(38-72)
Hwang et al., 2012	III	476	NR	NA	NA	NR	NR
Yeh et al., 2012	II	19	NR	NA	NA	26.9	(±4.17)
Erdil et al., 2013	III	1090	286	12	NR	43.4	(18-50)
Rai et al., 2013	II	12	9	NA	NA	40.8	(±12.1)
Choi et al.,2013	IV	186	NR	NA	NA	NR	NR
Yilar and Yildirim, 2014	III	90	50	NR^a	NR	58.3	(±8.74)
Sofu et al., 2016	III	128	65	49.2	(36-60)	NR	(60-75)
Kluczynski et al., 2017	II	256	106	12.3	(10.2-22.9)	53.4	(±7.9)
Krych et al., 2018	III	26	NR	66	(27.6-11.6)	54.7	(±9)
Lizaur-Urilla et al., 2019	II	258	NR	NR^a	NR	55.7	(45-60)
Longo et al., 2019	III	57	15	97.3	(61-145)	57.1	(34-75)

NR = not reported in the article; NA = not applicable, study was not on outcomes.

Mean follow-up was not listed but article claimed follow-up time point of at least 12 months.

The specific data that were extracted from the included articles when available included: study design, level of evidence, sample size, patient age and demographic characteristics, BMI classification, length of follow-up, mechanism of injury, postoperative outcome measures and results, and complication or failure rates. Again, the 2 authors (T.Z. and J.J.J.) independently extracted the data to an electronic spreadsheet (Microsoft Excel; Microsoft Corp., Redmond, WA) and the senior author (R.F.H.) resolved any discrepancies.

Statistical Analysis

All data were initially extracted into an electronic spreadsheet (Microsoft Excel). Descriptive statistics were generated using JMP Pro, Version 13 software (JMP, Version 13. SAS Institute Inc., Cary, NC). The Review Manager (RevMan) software (Version 5.3. Cophenhagen, Denmark: The Nordic Cochrane Centre, The Cochrane Collaboration, 2014) was used to determine proportions or mean differences using either fixed or random effects modeling, depending on the heterogeneity of the data analyzed. A P value of less than 0.05 was interpreted as statistically significant.

As in previous studies, to compare various knee-specific patient-reported outcomes (PROs) used by different studies, the scores were normalized to a scale out of 100 points where 0 is the worst and 100 is the best score. Improvement or change in a PRO score is defined as the postoperative score minus the preoperative score. Six studies reported on knee-specific PROs such as the Lysholm Knee Score (LKS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Knee Injury and Osteoarthritis Outcome Score (KOOS), International Knee Documentation Committee (IKDC) score, Oxford Knee Score (OKS), and the Tapper-Hoover score. The most commonly used knee-specific PROs were LKS (3 studies), WOMAC (2 studies), and IKDC (2 studies) while the other PROs were used by 1 study each ( Table 2 ).

Table 2.

All Patient-Reported Outcomes after Meniscectomy for Body Mass Index (BMI) Categories by Article.

Authors, Year	Outcome Measure	Normal (NL) BMI Result	Overweight (OW) BMI Result	Obese (OB) BMI Result	Conclusion/P-Values
Paradowski et al., 2005	Odds ratio (OR) of clinically relevant change in KOOS ADL	1.0 (ref)	2.0 (95% CI, 0.5-3.9)	1.8 (95% CI, 0.3-6.3)	Only the odds ratio for clinically relevant change in SF-35 Physical Function was found to be significantly increased in OW vs. NL BMI.
	OR of clinically relevant change in KOOS Pain	1.0 (ref)	2.0 (95% CI, 0.8-4.9)	1.8 (95% CI, 0.4-7.1)
	OR of clinically relevant change in SF-36 Physical Function	1.0 (ref)	2.4 (95% CI, 1.0-5.7)	0.1 (95% CI, 0.2-0.9)
	OR of clinically relevant change in SF-36 Pain	1.0 (ref)	1.9 (95% CI, 0.8-4.3)	0.6 (95% CI, 0.2-2.5)
Erdil et al., 2013	OKS preop	29.83 ± 2.76	29.1 ± 2.66	27.18 ± 1.97	∆OKS: OB vs. NL (P < 0.001), OW vs. NL (P < 0.001), and OB vs OW (P = 0.042). ∆LKS: OB vs. NL (P < 0.001), OW vs. NL (P < 0.001), and OB vs. OW (P = 0.013). ∆IKDC: OB vs. NL (P < 0.001), OW vs. NL (P < 0.001), and OB vs. OW (P = 0.0002).
	OKS postop	44.35 ± 3.6	42 ± 3.98	41.79 ± 3.55
	IKDC preop	49.58 ± 7.95	50.07 ± 5.74	46.09 ± 4.15
	IKDC postop	92.72 ± 4.28	89.44 ± 4.14	88.79 ± 3.26
	LKS preop	54.83 ±10.07	54.83 ± 10.07	47.95 ± 6.64
	LKS postop	91.42 ±4.34	91.42 ± 4.34	86.88 ± 3.26
Yilar and Yildirim, 2014	Perfect Tapper-Hoover	11	6	4	Tapper-Hoover: among BMI groups (P = 0.000). WOMAC: OB vs NL (P = 0.000), OW vs NL (NS) LKS: OB vs. NL (P = 0.000), OW vs. NL (NS). VAS: OB vs. NL (P = 0.000), OW vs NL (NS).
	Good Tapper-Hoover	6	9	9
	Moderate-Bad Tapper-Hoover	2	6	37
	WOMAC mean difference compared to normal BMI	NA	−8 ± 5.07	−17.34 ± 4.316
	LKS mean difference compared to normal BMI	NA	−5.03 ±3.559	−13.01 ± 3.029
	VAS mean difference compared to normal BMI	NA	0.58 ± 0.45	1.74 ± 0.383
Sofu et al., 2016	VAS preop	5.4 ± 1.3	5.9 ± 1.5	NR	VAS: postop OW vs. NL (P < 0.05) LKS: postop OW vs. NL (P < 0.05)
	VAS postop	1.8 ± 1.1	3.1 ± 1.5	NR
	LKS preop	47 ± 5.7	38 ± 6.6	NR
	LKS postop	79.6 ± 6.3	62.5 ± 5.7	NR
Kluczynski et al., 2017	VAS preop	4.2 ± 1.9	4.1 ± 2.1	4.9 ± 2.1	VAS: preop OB vs. NL (P = 0.01). All other comparisons were NS. WOMAC pain: preop OB vs. NL (P = 0.02). All other comparisons were NS. WOMAC stiffness: All comparisons NS. WOMAC PF: preop OB vs. NL (P = 0.04). All other comparisons were NS. KOOS pain: preop OB vs. NL (P = 0.02). All other comparisons were NS. KOOS other symptoms: All comparisons NS. KOOS sports/rec: All comparisons NS. KOOS QoL: preop OB vs. NL (P = 0.001) and change OW vs. NL (P = 0.04). All other comparisons were NS.
	VAS postop	1.4 ± 1.8	1.5 ± 2.1	1.5 ±1.9
	VAS change	2.7 ± 2.2	2.6 ± 1.9	3.3 ± 2.5
	WOMAC pain preop	61.3 ± 17.2	60.0 ± 16.3	56.2 ± 17.2
	WOMAC pain postop	87.9 ± 16	87.6 ± 15.8	86.6 ± 15.7
	WOMAC pain change	−26.3 ± 17.6	−27.6 ± 16.1	−29.8 ± 19.5
	WOMAC stiffness preop	48.7 ± 19.7	48.5 ± 18.7	45.3 ± 17.7
	WOMAC stiffness postop	79.4 ± 20.2	79.5 ± 20.6	76.4 ± 21.2
	WOMAC stiffness change	−29.8 ± 24.9	−31.0 ± 22.4	−30.2 ± 22.5
	WOMAC PF preop	62.8 ± 17.1	61.1 ± 17.3	55.8 ± 17.1
	WOMAC PF postop	88.7 ± 16.2	88.7 ± 15.2	86.0 ± 15.6
	WOMAC PF change	−25.3 ± 19.1	−27.5 ± 16.1	−29 ± 17.5
	KOOS pain preop	54 ± 15.1	53.1 ± 15.2	49.5 ± 14.9
	KOOS pain postop	84.4 ± 17.1	84.4 ± 17.7	83.1 ± 17.9
	KOOS pain change	−29.8 ± 18.1	−31.2 ± 16.5	−33 ± 18.2
	KOOS other symptoms preop	45.8 ± 12.6	48.5 ± 13.3	44.6 ± 10.8
	KOOS other symptoms postop	60.5 ± 15.4	60.0 ± 12.2	59.3 ± 12.9
	KOOS other symptoms change	−14.5 ± 15.6	−12.3 ± 13.6	−13.3 ± 18.2
	KOOS sports/rec preop	42.5 ± 21.6	40.2 ± 23.5	36 ± 22.8
	KOOS sports/rec postop	77.6 ± 23.3	77.4 ± 24.0	72.1 ± 26.1
	KOOS sports/rec change	−35.6 ± 28.5	−35.1 ± 26.6	−34.9 ± 26.2
	KOOS QoL preop	36.9 ± 17.0	32.1 ± 17.6	27.9 ± 18.3
	KOOS QoL postop	73.1 ± 23.0	74.5 ± 24.0	69.5 ± 24.9
	KOOS QoL change	−35.8 ± 24.9	−43.3 ± 23.9	−41.9 ± 25.3
Krych et al., 2018	IKDC postop	87.3 ± 5.9	NA	52.2 ± 8.8	OB vs. non-OB (P = 0.0002)
Lizaur-Urilla et al., 2019	OR of dissatisfaction	1.0 (ref)	NA	2.6 (95% CI, 1.7-4.9)	OB vs. non-OB (P = 0.035)

NR = not reported in article; NS = not significant with P > 0.05; CI = confidence interval; preop = preoperative; postop = postoperative; OB = obese; OW = overweight; NL = normal; OKS = Oxford Knee Score; IKDC = International Knee Documentation Committee; LKS = Lysholm Knee Score; WOMAC = Western Ontario McMaster Universities Osteoarthritis Index; PF = physical function; QoL = quality of life; VAS = visual analogue scale; KOOS = Knee Injury and Osteoarthritis Outcome Score.

Results

The final cohort, after excluding duplicate patient cohorts, consisted of 3,091 patients. Of these patients, 59.0% (n = 1,823) were male and 41.0% (n = 1,268) were female. A total of 618 patients were categorized as obese and 636 patients were categorized overweight. However, there were various definitions or thresholds for BMI categorization (Supplemental Appendix A). Most studies included 3 groups for normal BMI, overweight BMI, and obese BMI. However, a few studies used only 2 BMI groups such as nonobese versus obese or normal versus overweight,^22-24 and 2 studies had additional groups such as morbidly obese at BMI ≥40 kg/m² or underweight at BMI <18.5 kg/m².^25,26 The range of mean follow-up in the included studies was 12 to 216 months.

Erdil et al.²⁷ and Sofu et al.²² reported on pre- and postoperative LKS scores, and our random model effects demonstrated worse preoperative scores in overweight/obese versus normal BMI patients with a mean difference of -6.06 [95% CI, −11.70 to −0.42]. However, there were no significant differences in final postoperative or improvement of scores with a mean difference of −9.57 [95% CI, −24.23 to 5.09] and −0.47 [95% CI, −4.99 to 4.05], respectively ( Fig. 2 ).^22,27 Similarly, when evaluating the normalized PRO scores with the addition of data from Kluczynski et al. ( Fig. 3 ),²⁸ overweight/obese BMI was not associated with any significant differences in improvement or final postoperative normalized PRO scores with a mean difference of −2.80 [95% CI, −8.45 to 2.85] and −7.52 [95% CI, −17.97 to 2.94], respectively. But looking at obese versus notobese BMI ( Fig. 4 ), worse postoperative scores were more likely with a mean difference of −4.57 [95% CI, −5.33 to −3.81], though no differences were found regarding improvement of PRO scores with a mean difference of 0.75 [95% CI, −0.44 to 1.94].

Figure 2.

Overweight/obese versus normal body mass index (BMI) groups: (A) preoperative Lysholm Knee Score (LKS), (B) postoperative LKS, (C) change in LKS.

Figure 3.

Overweight/obese versus normal body mass index (BMI) groups: (A) change in normalized patient-reported outcomes (PROs), (B) postoperative normalized PROs.

Figure 4.

Obese versus normal body mass index (BMI) groups: (A) change in normalized knee-specific patient-reported outcomes (PROs), (B) postoperative normalized knee-specific PROs.

There were a few significant differences in other knee-specific PROs reported by singular studies that could not be included in our analyses ( Table 2 ). Kluczynski et al.²⁸ found that worse preoperative KOOS pain, KOOS QOL, WOMAC pain, and WOMAC physical function scores was associated with obese BMI. Similarly, Yilar and Yildirim²⁹ noted that patients with BMI >29 kg/m² were more likely to have a worse postoperative WOMAC scores compared with patients with BMI < 25 kg/m². They also reported increased frequency of moderate or bad Tapper-Hoover scores in higher BMI groups. Both Erdil et al.²⁷ and Krych et al.²³ observed that increased improvement in IKDC scores was associated with obese BMI. Finally, Erdil et al.²⁷ also showed better improvement in OKS in obese and overweight patients when compared with the normal BMI group.

With regard to pain, Sofu et al.²² and Kluczynski et al.²⁸ reported on pre- and postoperative visual analogue scale (VAS) for knee pain, and our random-effects model demonstrated that overweight/obese BMI was associated with worse preoperative VAS scores at a mean difference of 0.43 [95% CI, 0.07 to 0.79] ( Fig. 5 ), but not worse postoperative or improvement in VAS scores (0.72 [95% CI, −0.46 to 1.89] and −0.28 [−1.32 to 0.76], respectively). Yilar and Yildirim²⁹ reported only on the mean difference in postoperative VAS pain score between increased and normal BMI groups, which could not be included in the analysis, but the authors reported that this difference was significant ( Table 2 ).

Figure 5.

Overweight/obese versus normal body mass index (BMI) groups: (A) preoperative visual analogue scale (VAS), (B) postoperative VAS, (C) change in VAS.

Regarding other outcome metrics, Paradowski et al.²⁰ looked at the odds ratio of clinically relevant change in Short Form 36 (SF-36) Physical Function and Pain scores, reporting no significant differences among BMI groups except for increased change in SF-36 physical function scores for overweight BMI. Lizaur-Urilla et al.²⁴ found that patients with BMI >30 kg/m² were more likely to be dissatisfied based on a Likert-type scale survey ( Table 2 ).

For objective outcomes, Kluczynski et al.²⁸ was the only study to evaluate pre- and postoperative extension deficit, flexion, and presence of knee effusion ( Table 3 ). The authors did not find any significant differences regarding neutral extension deficit but did observe that obese BMI patients were more likely to have decreased flexion both pre- and postoperatively. However, no significant difference was found when comparing change in flexion. Additionally, they found that both obese and overweight patients were more likely to have knee effusion preoperatively.

Table 3.

Objective Outcome Measures of Meniscectomy for Body Mass Index (BMI) Categories by Article.

Authors, Year	Outcome Measure	Normal BMI Result	Overweight BMI Result	Obese BMI Result	Conclusion
Kluczynski et al, 2017	Neutral extension deficit preop	2.4 ± 3	2.8 ± 3.2	3.3 ± 3.6	No statistically significant differences in neutral extension were found among BMI groups. Obese patients were more likely to have decreased flexion when compared to normal BMI patients (P = 0.003). Both overweight and obese patients were more likely to have knee effusion before surgery than normal BMI patients (P = 0.003 and P = 0.03)
	Neutral extension deficit postop	1.3 ± 2	2.1 ± 3	2.4 ± 2.5
	Flexion preop	132.3 ± 16.5	126.6 ± 16.1	121.8 ± 22.6
	Flexion postop	134.5 ± 8.3	130.2 ± 7.7	128.1 ± 7.1
	Knee effusion preop	17	51	56
	Knee effusion postop	3	14	11

preop = preoperative; postop = postoperative.

Several studies evaluated the incidence of degenerative joint disease following APM ( Table 4 ) at a mean or minimum follow-up of 5 years postoperatively. Two articles^18,30 reported odd ratios for radiographic tibiofemoral OA at latest follow-up; however, our random model effects did not demonstrate a significantly increased odds ratio (OR) for obese when compared to normal BMI (OR, 5.34 [95% CI, 0.75 to 38.11]) or overweight/obese versus normal BMI (OR, 1.52 [95% CI, 0.99 to 2.32]) as seen in Figure 6 . Regarding other measures of OA that could not be included in our analysis, Englund and Lohmander¹⁸ also evaluated patellofemoral OA as well as symptomatic tibiofemoral OA, finding increased ORs associated with obese BMI ( Table 4 ). Lizaur-Utrilla et al²⁴ also observed increased OR for progression of OA in obese patients, as measured by change in Kellgren-Lawrence (K-L) grade pre- and postoperatively.

Table 4.

Osteoarthritis Outcomes of Meniscectomy for Body Mass Index (BMI) Categories by Article.

Authors, Year	Outcome Measure	Normal BMI Result	Overweight BMI Result	Obese BMI Result	Conclusion
Englund et al., 2003	Odds ratio of radiographic tibiofemoral OA	1.0 (ref)	1.3 (95% CI, 0.7-2.7)	3.7 (95% CI, 1.2-11.2)	Increased odds ratio for radiographic tibiofemoral OA as well as for radiographic and symptomatic tibiofemoral OA in the obese BMI group.
Englund et al., 2003	Odds ratio of radiographic and symptomatic tibiofemoral OA	1.0 (ref)	2.4 (95% CI, 1.0-5.8)	4.0 (95% CI, 1.3-12.8)
Englund and Lohmander, 2004	Odds ratio of radiographic tibiofemoral OA	1.0 (ref)	1.2 (95% CI, 0.7-2.1)	2.5 (95% CI, 1.1-5.7)	Increased odds ratio for radiographic tibiofemoral OA in the obese BMI group, Increased odds ratio for symptomatic tibiofemoral OA in both the overweight and obese BMI groups. Increased odds ratio for radiographic and symptomatic tibiofemoral and patellofemoral OA for both overweight and obese BMI groups.
	Odds ratio of symptomatic tibiofemoral OA	1.0 (ref)	2.6 (95% CI, 1.2-4.6)	3.0 (95% CI, 1.3-7.0)
	Odds ratio of radiographic and symptomatic tibiofemoral and patellofemoral OA	1.0 (ref)	2.4 (95% CI, 1.2-4.8)	3.9 (95% CI, 1.6-9.8)
Englund and Lohmander, 2005	Odds ratio of radiographic patellofemoral OA	1.0 (ref)	1.0 (95% CI, 0.5-2.0)	2.8 (95% CI, 1.2-6.4)	Increased odds ratio for obese BMI patients but not for overweight BMI.
Lizaur-Urilla et al., 2019	Odds ratio of OA progression	1.0 (ref)	NA	2.5 (95% CI, 1.4-4.6)	Increased odds ratio for BMI >30 kg/m².
Longo et al., 2019	Prevalence of medial OA preop	21.24%	13.04%	18.18%	Both overweight and obese groups had significant increases in medial compartment OA prevalence from pre- to postoperatively (P = 0.0097 and P = 0.0007). No significant increase in medial OA prevalence was detected in the normal BMI group (P = 0.02365). Additionally, no significant increase in lateral compartment OA prevalence was seen for normal, overweight, or obese groups (P = 0.5594, P = 0.2063, and P = 0.5455)
	Prevalence of medial OA postop	50%	56.52%	100%
	Prevalence of lateral OA preop	16.66%	14.28%	20%
	Prevalence of lateral OA postop	50%	42.85%	80%

preop = preoperative; postop = postoperative; NA = not applicable; OA = osteoarthritis.

Figure 6.

Radiographic osteoarthritis (OA): (A) obese versus normal body mass index (BMI) groups, (B) overweight/obese versus normal BMI groups.

Complication or failure rates after APM stratified by BMI were studied by Erdil et al.²⁷ and Krych et al.²³ ( Table 5 ). Erdil et al.²⁷ reported that the obese BMI group had a significantly higher percentage of patients who experienced early unspecified complications after meniscectomy at 36.7% (P = 0.037). Similarly, Krych et al.²³ described that the obese BMI group also had significantly higher failure rate compared with the nonobese BMI group (94.4% vs. 44.4%, P = 0.004). They defined failure as progression to total knee arthroplasty (TKA) or an IKDC score less than 75.4 points.²³

Table 5.

Failures and Complications for Body Mass Index (BMI) Categories by Article.

Authors, Year	Normal BMI			Overweight BMI			Obese BMI
Authors, Year	n	Failure, n (%)	Complication, n (%)	n	Failure, n (%)	Complication, n (%)	n	Failure, n (%)	Complication, n (%)
Erdil et al., 2013	483	NR	149 (30.8)	321	NR	87 (27.1)	286	NR	105 (36.7)
Krych et al., 2018	NR	NR (44.4)	NR	NR	NR	NR	NR	NR (94.4)	NR

NR = not reported.

Of the studies investigating differences in pathoanatomy or pathophysiology associated with increased BMI, 3 studies looked at presence of medial meniscus posterior root tears and suggested that there may be an association with obese BMI ( Table 6 ).^25,26,31 Additionally, Yeh et al.³² observed that professional basketball athletes with a BMI >25 kg/m² had increased risk of lateral versus medial meniscus tears in addition to an overall increased risk of meniscal injury. Last, Rai et al.³³ observed differences in meniscal gene expression among BMI categories in patients undergoing meniscectomy.

Table 6.

Pathophysiology of Meniscal Injury for Body Mass Index (BMI) Categories by Article.

Authors, Year	Outcome Measure	Normal BMI Result	Overweight BMI Result	Obese BMI Result	Conclusion
Ozkoc et al., 2008	n (%) of MMPRT	1 (1.5)	12 (17.9)	52 (79.6)	Ratio of obese patients with MMPRT was much higher than regional obesity rate but no P-values were reported.
Hwang et al., 2012	MMPRT odds ratio	1	1.746 (95% CI, 0.821-3.713)	4.929 (95% CI, 1.160-20.955)	No significant between overweight and normal BMI groups (P = 0.148). Significant difference between obese and normal BMI groups (P = 0.031).
Yeh et al., 2012	Injury rate ratio	1	1.6 (95% CI, 1.2-2.3)	NA	Significantly higher risk of injury in patients with higher BMI (P < 0.05). Significantly higher risk of lateral vs medial meniscal tear in individuals with higher BMI (P < 0.05).
Yeh et al., 2012	Lateral vs. medial meniscus injury ratio	1	1.7 (95% CI, 1.03-2.29)	NA
Choi et al., 2013	n of MMPRT	41	46	4	Significant difference in the frequency distribution of BMI between MMPRT and horizontal tears (P = 0.007)
Choi et al., 2013	n of horizontal tears	63	26	4
Rai et al., 2014	% differently expressed genes compared with normal BMI group	NA	2.8	3.4	Differences in expressed genes among BMI groups were largely related to metabolism. Largest difference in expressed genes was between obese and overweight groups. All included gene transcripts showed fold changes of ≥1.5 and P < 0.05.
Rai et al., 2014	% differently expressed genes compared with overweight BMI group	NA	NA	4.7

MMPRT = medial meniscus posterior root tear; NR = not reported; NA = not applicable.

Discussion

As the prevalence of obesity continues to rise, it is important for orthopedic surgeons to understand how obesity may affect evaluation, treatment, and surgical outcomes of injuries such as meniscal tears. To the authors’ knowledge, this study is the first meta-analysis on the surgical outcomes associated with obese BMI categorization in patients undergoing APM.

Regarding knee-specific PROs, this study suggests that although obesity may be associated with worse pre- and postoperative scores, there is no strong evidence for any differences in score improvement compared with nonobese patients. Thus, these findings suggest that at short- to mid-term follow-up, obese patients may have similar improvement of symptoms and/or function after meniscectomy as patients with normal BMI. If meniscectomy successfully removes a meniscal tear as the culprit for causing pain and mechanical symptoms, it is plausible that BMI may not significantly affect how much relief a patient experiences in the short-term follow-up period.

In our analysis of the development of radiographic OA as a long-term outcome/complication of APM, there were no significantly higher ORs associated with obese and/or overweight BMI. However, the results were close to statistical significance, and a few studies noted differences individually therefore, these studies may be underpowered. Also, it was variable whether studies categorized OA as being clinically symptomatic in addition to radiographically evident, and these studies did not consistently indicate if OA was present preoperatively as well as at follow-up. Thus, future studies should aim to delineate symptomatic vs non-symptomatic OA both pre- and postoperatively.

Overall, there is a lack of studies that report on surgical complication or failure rates after APM by BMI category. Articles in this review indicated higher rates of complications and failure in obese patients but did not include a statistical analysis. Based on studies of BMI as a risk factor in other types of surgeries, there could be a theoretical increased risk of poor wound healing and infection.^13,34 However, in general knee arthroscopy is considered to have an overall low complication rate; therefore, individual studies are likely to be underpowered to detect differences by BMI categories. In the context of meniscectomy, failure can encompass revision/further meniscal surgery, high tibial osteotomy, conversion to TKA, or little to no relief of symptoms.^18,21,22,24 Thus, more failures might be expected in the obese population due to increased joint loading forces or altered biomechanics that contribute to either meniscal retear or the development of OA.^35,36

Regarding possible differences in pathoanatomy of meniscal tears, there is some evidence obesity may be associated with a higher risk of medial meniscal root tears. This could be due to differences in biomechanics and/or mechanism of injury as elevated BMI is likely to chronically expose the meniscus to higher forces that could act with a greater degree on the medial meniscus posterior horn due to its lack of mobility and close attachment to the tibia.³⁷ While the studies examining this did not report the treatment of these tears, we felt it was important to include these findings in this article as part of our secondary goals. APM in the setting of a root tear has questionable utility, and meniscal root tears are best treated with root repair in most patients. In another study, an association between lateral versus medial meniscal tears in National Basketball Association athletes with a BMI >25 kg/m² was reported.³² However, BMI is a poor measurement of body fat content in professional athletes due to increased muscle mass and therefore, this study is unlikely to be generalizable to a normal population.³⁸ Last, 1 study provided evidence that obesity may be associated with changes in gene expression related to meniscal tissue degeneration.³³ However, the tissue specimen samples were taken at time meniscectomy so it is unknown if these genetic differences are baseline or in response to injury.

As with any meta-analysis, this study has several inherent limitations such as being limited to the strength of existing literature. The included studies used different definitions for BMI categories, osteoarthritis progression, or surgical failure. Additionally, PROs were not reported in a uniform manner. Another limitation is that many articles were excluded for using BMI as a continuous variable. However, the results from these types of analyses were inconsistent in indicating whether BMI was an independent predictor of PROs after meniscectomy. Possible reasons for this include a nonlinear relationship between BMI and PROs, underpowered studies, or the use of only postoperative versus change in PRO scores. Finally, the inclusion criterion of 1-year follow-up may be short for assessment of certain metrics. However, a minimum or mean follow-up time of 5 years was utilized in the studies investigating the development or progression of OA.

In conclusion, obesity is associated with worse knee function after APM, and patients with elevated BMI have worse preoperative knee pain and function. However, there is no difference in amount of pre- to postoperative improvement in symptoms, suggesting that APM can be as beneficial to overweight and obese patients as to patients with normal BMI. Further prospective research with longer follow-up is necessary to determine the comparative effectiveness of APM in patients with elevated BMI.

Supplemental Material

Appendix_A_BMI_definitions – Supplemental material for Outcomes of Partial Meniscectomy in Obese Patients: A Systematic Review and Meta-Analysis

Supplemental material, Appendix_A_BMI_definitions for Outcomes of Partial Meniscectomy in Obese Patients: A Systematic Review and Meta-Analysis by Tina Zhang, Julio J. Jauregui, Michael Foster, Jonathan D. Packer, Sean J. Meredith, Natalie L. Leong and R. Frank Henn in CARTILAGE

Footnotes

Supplemental material for this article is available on the Cartilage website at .

Acknowledgments and Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Declaration of Conflicting Interests

The author(s) declared the following potential conflicts of interest with respect to the research, authorship, and/or publication of this article: S.J.M. and J.P. are board or committee members of the American Orthopaedic Society for Sports Medicine. R.F.H. has previously received research support from Arthrex, Inc.

ORCID iDs

Tina Zhang

Sean J. Meredith

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