Preoperative Medial Meniscus Extrusion on Magnetic Resonance Imaging Is Associated With a Tendency Toward Varus Shifting of Open-Wedge High Tibial Osteotomy: A Minimum 5-Year Follow-Up Study.

Purpose: To investigate serial changes in postoperative alignment over 5 years after open-wedge high tibial osteotomy (OWHTO) and to identify risk factors associated with alterations in the postoperative weightbearing line (WBL) ratio.

Methods: Patients who underwent OWHTO during 2011-2017 were retrospectively reviewed. The inclusion criteria were (1) follow-up duration ≥5 years and (2) serial postoperative longstanding hip-to-ankle radiographs to evaluate alignment alterations. The WBL ratio was measured preoperatively and at 3 months, 6 months, 1 year, and 5 years postoperatively to evaluate serial changes. Alterations in the WBL ratio were analyzed using a linear mixed model, considering potential risk factors including International Cartilage Repair Society grades of each compartment and medial meniscus extrusion (≥3 mm). Clinical outcomes were assessed using the Knee Society objective and functional scores, and the correlations between clinical outcomes and alignment alteration were examined.

Results: A total of 78 knees were investigated. During the study period, the overall WBL ratio decreased by 5.5% ± 7.2%, signifying varus shifting, from 58.6% ± 11.5% at 3 months postsurgery to 51.5% ± 12.7% at 5 years postsurgery. Based on univariate regression analyses, International Cartilage Repair Society grades of the medial compartment and medial meniscus extrusion were included in a linear mixed model regarding alignment alteration. The model identified medial meniscus extrusion as a significant risk factor after adjusting for time (P < .001). Medial meniscus extrusion also had a significant interaction with time (P < .001), indicating greater alignment alteration in cases of medial meniscus extrusion. The extrusion was noted in 68 of 78 knees.

Conclusions: In the midterm following OWHTO, the overall alignment had a tendency toward varus shifting. A linear mixed model found that preoperative medial meniscus extrusion on magnetic resonance imaging is associated with the tendency.

Level of evidence: Level III, retrospective cohort study.