Successful Medial Meniscal Repair Reduces Knee Pain 10 Years After Anterior Cruciate Ligament Reconstruction: Exploring the Consequences of Subsequent Surgery With Causal Mediation Analysis in the MOON Cohort

Background: Medial meniscal repair performed at the time of primary anterior cruciate ligament reconstruction (ACLR) has been shown to be significantly associated with subsequent surgery, and subsequent surgery has been associated with increased Knee injury and Osteoarthritis Outcome Score (KOOS) pain score and decreased patient satisfaction. Hypothesis/Purpose: The purpose was to determine if medial meniscal repair decreases KOOS pain 10 years after ACLR and to assess the consequences of subsequent surgery on the development of KOOS pain. The authors hypothesized that medial meniscal repair performed at the time of primary ACLR decreases the likelihood of developing KOOS pain. It was further hypothesized that surgery performed subsequent to medial meniscal repair and primary ACLR increases KOOS pain 10 years after ACLR. Study Design: Cohort study; Level of evidence, 2. Methods: Our inclusion criteria were all patients undergoing unilateral primary ACLR from 2002 to 2008 who were enrolled in the Multicenter Orthopaedic Outcomes Network without a history of medial or lateral meniscal surgery and contralateral ACLR. Causal mediation analysis using R software (Version 4.2.3) was employed to compare 2 effects on the development of significant knee pain, as represented by a KOOS pain score <80, at 10-year follow-up: (1) medial meniscal repair for longitudinal tears >10 mm in medial-to-lateral length and (2) medial meniscal excision at baseline of ACLR. A directed acyclic graph was constructed to provide a qualitative representation of the influence of known confounders that have been shown to affect the outcome of interest. Missing data were multiply imputed using multivariate imputation by chained equations. All tests were 2-sided, assuming a type I error rate of .05. Results: In total, 2387 participants (1074 female [45%]; 1313 male [55%]) were included in the final analysis. In 1502 (62.9%) cases, there was no medial meniscal tear reported. Of the 885 cases with medial meniscal tears, no treatment was performed in 109 (12.4%), meniscal excision was performed in 396 (44.7%), and meniscal repair was performed in 380 (42.9%). An overall 1825 of 2387 (76.5%) patients reported KOOS pain at 10-year follow-up: 252 (13.8%) had KOOS pain <80 and 1573 had ≥80. In the KOOS pain <80 group, 75 (29.8%) had subsequent surgery. In the KOOS pain ≥80 group, 223 (14.2%) had subsequent surgery. The step-by-step approach to causal mediation analysis demonstrated that a medial meniscal procedure (ie, no treatment for the tear, repair, or excision) significantly affected the likelihood of subsequent surgery (χ 2 = 28.9; P < .001) and subsequent surgery significantly increased the likelihood of KOOS pain <80 (χ 2 = 17.3; P < .001). However, the direct effect of a successful medial meniscal repair without subsequent surgery decreased the likelihood of KOOS pain <80 by 7.1% when compared with medial meniscal excision (95% CI, –13.3% to −1%; P = .024). When subsequent surgery was performed after medial meniscal repair and ACLR, the likelihood of KOOS pain <80 increased by 2.9% (95% CI, 1.1%-5.3%; P < .001.) Conclusion: Successful medial meniscal repair performed at the time of primary ACLR decreased clinically significant knee pain 10 years postoperatively. However, the mediating effect of subsequent surgery was significant and diminished the overall contribution of medial meniscal repair in decreasing the likelihood of KOOS pain. Continued efforts should be made to decrease the likelihood of subsequent surgery after medial meniscal repair performed at the time of primary ACLR.