Lateral meniscus extrusion on preoperative MRI and its impact upon mid-term clinical outcomes following mobile-bearing unicompartmental knee arthroplasty.

Abstract

The presence of full-thickness cartilage in the lateral compartment on valgus stress radiography is a criterion for medial mobile-bearing unicompartmental knee arthroplasty (UKA). However, the appropriateness of medial UKA is uncertain when preoperative MRI shows extrusion of the lateral meniscus. We therefore assessed how preoperative MRI-detected lateral meniscus extrusion affects mid-term functional outcomes after mobile-bearing UKA. We retrospectively reviewed the records of our patients that underwent mobile-bearing medial UKA between January 2017 and December 2019. Crema's classification system was used to assess MRI of the lateral meniscus, categorizing patients as either grade 0 or ≥ grade 1. We preoperatively evaluated patient-reported outcomes using the Oxford knee score and Knee Society functional score, and then again at the latest follow-up. We also measured range of motion pre- and postoperatively. We compared preoperative individual data with outcome data obtained for at least three years. The lateral meniscus extrusion group included 19 knees, and the remainder included 98 knees. Clinical outcomes were similar between these groups (<i>p</i> > 0.05). No progression of lateral arthritis was observed in either group during the follow-up period. Excluding UKA as an option for cases with lateral meniscus extrusion findings on preoperative MRI may require reconsideration.