Perceived Instability Is Associated With Strength and Pain, Not Frontal Knee Laxity, in Patients With Advanced Knee Osteoarthritis

Abstract

Background Increased varus/valgus laxity and perceived knee instability are independently associated with poor outcomes in people with knee osteoarthritis. However, the relationship between laxity and perceived instability is unclear. Objective To assess whether knee extensor strength, pain, and knee laxity are related to perceived knee instability in patients with advanced knee osteoarthritis. Methods This was a secondary analysis of a prospective observational cohort study of 35 patients (24 female; mean ± SD age, 60 ± 8 years; body mass index, 33 ± 5 kg/m2) with knee osteoarthritis awaiting total knee arthroplasty (36 knees). Within 1 month before arthroplasty, we measured isometric knee extension strength and self-reported knee pain (using the Knee injury and Osteoarthritis Outcome Score pain subscale). Patients rated their perception of knee instability as moderate to severe (n = 20) or slight to none (n = 15 patients, n = 16 knees) using the Knee Outcome Survey. We measured intraoperative varus/valgus knee laxity. Results Lower knee extension strength (P = .01) and greater pain (P<.01) were associated with the perception of moderate to severe knee instability. Laxity was not related to perceived knee instability (P = .63). Conclusion Knee extension strength and pain were associated with perceived instability in people with advanced osteoarthritis. Varus/valgus laxity was not related to perceived knee instability. Level of Evidence Level 2, prognostic. J Orthop Sports Phys Ther 2019;49(7):513–517. doi:10.2519/jospt.2019.8619