Medial opening wedge high tibial osteotomy (OWHTO) is a useful treatment for medial osteoarthritis. However, OWHTO sometimes causes a change in tibial slope in the sagittal plane. Although several studies have described the effects of the tibial slope on the biomechanics of the knee, including the anterior cruciate ligament (ACL), there has been little study of the magnetic resonance imaging (MRI) visible changes occurring to the native ACL and the factors affecting them after OWHTO.

We hypothesized that morphologic MRI changes to an uninjured ACL after OWHTO would be associated with increased medial tibial plateau bony slope.

Thirty-three patients who underwent OWHTO and pre/postoperative MRI were included in this retrospective study. The mean period of follow-up MRI was 22.35 (±14.78) months. The patients were divided into two groups according to the occurrence of postoperative ACL morphologic MRI changes defined as mucoid degeneration, ganglion cyst occurrence, or change in the ACL fiber shape (stationary group n=21, altered group n=12). The medial tibial plateau bony slope (MTS) and anterior tibial translation (ATT) were evaluated on MRI. Logistic regression analysis was used to determine factors affecting the occurrence of postoperative ACL morphologic changes.

Postoperative MTS and the difference between pre- and post values (ΔMTS), postoperative ATT and the difference between pre- and post values (ΔATT) were significantly different between stationary and altered groups. ΔMTS was associated with postoperative morphologic changes to the ACL (odds ratio: 0.30, 95% confidence interval=0.11–0.82, p=0.019).

The occurrence of morphologic ACL change after OWHTO is associated with the amount of MTS change.

III, Retrospective comparative study.