Clinical outcomes of patients with residual medial osteophytes following mobile bearing unicompartmental knee arthroplasty

Abstract

Introduction: The surgical technique used in unicompartmental knee arthroplasty (UKA) is crucial for achieving good short and long term clinical outcomes. The medial mobile bearing UKA has shown excellent clinical outcomes and survivorship. But release of the medial collateral ligament during entering joint is cause of mobile bearing dislocation in short term outcomes and lateral compartment osteoarthritis may occur in the mid to long term outcomes. Removing all osteophytes at the time of UKA is sometime impossible due to their large size and extend to the inferior part of medial tibial plateau and removing them completely my result in release of the MCL. But no data exist on clinical outcomes in such patients.

Methods: We conducted a prospective study from 2010 to 2015 of patients undergoing mobile bearing UKA and classified them in to two groups: those with (Gp1) and without (Gp2) residual osteophytes. Osteophyte size was measured using Hernborg's technique. The primary outcomes were pain score, functional score, and knee scores and the presence of reported medial knee pain.

Results: 176 patients who underwent 199 mobile bearing UKAs were recruited: Gp1 = 42 patients (46 knees) and Gp2 = 134 patients (153 knees). Residual osteophyte sizes ranged from 2.13-9.42 mm (mean 4.12). The mean Gp1 Gp2 pain score (49.04, 48.92, p = 0.84), functional score (83.75, 84.04, p = 0.83) and knee score (89.86, 98.7, p = 0.0.78) scores were almost identical and no one complained of medial joint pain. Followed up ranged from 2 - 7 years (mean 4.23). No patients were lost to follow up.

Conclusion: The patients with residual osteophytes of length less than 9 mm had good and similar clinical outcomes as patients without residual osteophytes following mobile bearing UKA.

Level of evidence: Level II-2, evidence obtained from well-designed cohort studies or case-control studies, preferably from more than one center or research group.

Fig 1. The size of residual osteophyte was measured from the medial cortex of the tibial plateau to the outer margin of osteophyte.

Fig 2. Only the anterior capsule was released when entering the knee joint (triangle shape).

Removal of as much of the anteromedial osteophyte was done but always keeping above the insertion of the medial collateral ligament MCL and capsule (A). The anteromedial cortex was identified and used to position of the tibial component to prevent implant overhang. The posteromedial osteophyte (arrow) was difficult to remove without releasing MCL (B). The preoperative radiographic showing the large medial osteophyte (C). The postoperative radiograph (D) showing the residual osteophyte.