Abstract
BACKGROUND: Mucoid degeneration (MD) of the anterior cruciate ligament (ACL) is a recognized pathology marked by collagen fiber degradation and infiltration of a mucoid substance, which may be associated with the subsequent development of knee osteoarthritis. PURPOSE: To investigate the association between progressive MD-ACL and intermediate-term outcomes following high tibial osteotomy (HTO) for medial compartment knee osteoarthritis. STUDY DESIGN: Cohort study; Level of evidence, 3. METHODS: The authors identified 322 patients who underwent medial opening-wedge HTO for medial compartment osteoarthritis with an intact ACL between 2015 and 2022. All patients underwent second-look arthroscopy approximately 2 years after the initial HTO, with a mean follow-up of 72.5 months (range, 27.0-116.0) from the initial HTO to the latest evaluation. Patients with MD-ACL observed during second-look arthroscopy were classified as the MD-ACL group, while those with a normal ACL served as the control group. Propensity score matching was conducted by age, sex, body mass index, and the interval between HTO and second-look arthroscopy, resulting in 43 matched patients in each group. Clinical outcomes were evaluated with the International Knee Documentation Committee (IKDC) score and Knee injury and Osteoarthritis Outcome Score (KOOS). RESULTS: Both groups showed significant improvements in clinical outcomes at second-look arthroscopy as compared with baseline (all P < .001). However, at second-look arthroscopy, the MD-ACL group had significantly worse IKDC scores (mean ± SD, 61.0 ± 13.9 vs 68.8 ± 14.4; P = .020), KOOS pain (70.1 ± 19.1 vs 78.6 ± 15.0; P = .023), KOOS symptoms (67.3 ± 19.5 vs 76.1 ± 13.6; P = .022), KOOS activities of daily living (70.7 ± 18.9 vs 80.4 ± 15.5; P = .011), and range of motion (128.8°± 8.9° vs 136.1°± 7.8°; P < .001) as compared with the control group. At the latest follow-up, outcomes in the control group remained stable without significant decline (P = .568), while the MD-ACL group demonstrated a clear tendency toward deterioration, including a significant decline in IKDC scores (61.0 ± 13.9 at second-look arthroscopy to 57.4 ± 12.3 at the latest follow-up; P = .025). The survival rate at a mean follow-up of 72.5 months was 97.6%, with no significant difference between groups (P = .400, log-rank test). Multivariate regression analysis identified smaller intercondylar notch geometry (P = .003), increased postoperative medial proximal tibial angle (P = .031), and larger changes in posterior tibial slope (P = .004) as significant predictors of MD-ACL development. CONCLUSION: The development of MD-ACL was associated with poorer clinical outcomes after HTO over an intermediate follow-up period. Smaller intercondylar notch geometry, increased medial proximal tibial angle, and larger changes in posterior tibial slope were significant predictors of MD-ACL development. These findings highlight the importance of careful preoperative planning and meticulous attention to surgical techniques that avoid excessive increases in medial proximal tibial angle and PTS, thereby improving HTO outcomes.