Summary

Superficial medial collateral ligament transection in open wedge high tibial osteotomy effectively enlarged the medial joint space width to 9.2 mm in 20° knee flexion, facilitating medial meniscus procedures, furthermore it returned to pre-transection levels after plate fixation.

Abstract

Objectives: Treatment strategy for meniscal lesion in unicompartmental knee osteoarthritis has not been established in clinical practice. While repairing the medial meniscus (MM) during opening wedge high tibial osteotomy (OWHTO) can restore meniscal function and reduce femorotibial contact pressure, approach to the posterior portion of the MM is known as a risk factor for iatrogenic chondral damage due to narrowed medial joint space in osteoarthritic knees. On the other hand, OWHTO often involves transecting or releasing the superficial medial collateral ligament (sMCL), however, whether or to what extent sMCL transection effectively widens the medial joint space for meniscal repair is unclear. The purpose of this study was to investigate changes in minimum joint space width (mJSW) due to sMCL transection during OWHTO.

Methods

We included 44 knees of 43 participants, who underwent OWHTO for unicompartmental knee osteoarthritis, in the final statistical analysis. During the OWHTO, the 1st layer was incised along with the superior border of pes anserinus and the pes was retracted posteriorly to expose the sMCL. Then, the level of osteotomy was determined by fluoroscopy, and the sMCL was transected using a chisel and knife. Intraoperative fluoroscopic evaluations of mJSW were recorded under neutral, valgus stress, and varus stress positions at knee extension and 20° knee flexion before sMCL transection, after transection, and after plate fixation. Changes in mJSW and increases in valgus stress were calculated and compared using analysis of variance. Linear regression analysis was performed to investigate the related factors for increased mJSW after transection.

Results

Maximum mJSW occurred during valgus stress after sMCL transection in 20° flexion and returned to baseline after plate fixation. Under the valgus stress condition, the mean mJSW before transection was 5.1 ± 0.9 mm in extension and 5.5 ± 1.1 mm in 20° flexion. It increased significantly after transection to 7.8 ± 1.4 mm (p < 0.001) and 9.2 ± 2.1 mm (p < 0.001), respectively. Notably, a sMCL transection could obtain 2.7 ± 1.5 mm additional mJSW in extension and 3.5 ± 2.3 mm in 20° flexion. Their increasing ratios were 227.4% and 281.2% for extension and 20° flexion, respectively. Regression analysis showed that increased mJSW after transection in extension positively correlated with the knee extension angle (p = 0.032). Conversely, no significant related factors were observed for the mJSW, which increased with sMCL transection in 20° flexion.

Conclusions

This study demonstrates that sMCL transection during OWHTO effectively enlarged the mJSW, achieving a significant increase of 3.8 mm compared to pre-transection values. This expanded space, reaching a post-transection maximum of 9.2 mm, provides sufficient access for safe and efficient MM repair procedures. Notably, plate fixation effectively restored mJSW to its pre-transection level. These findings suggest that sMCL transection presents a valuable strategy for facilitating posterior medial meniscus repair in OWHTO while maintaining joint stability.