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

Background: 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. Methods: 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. Results: The lateral meniscus extrusion group included 19 knees, and the remainder included 98 knees. Clinical outcomes were similar between these groups ( Conclusion: Excluding UKA as an option for cases with lateral meniscus extrusion findings on preoperative MRI may require reconsideration.