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

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/m(2)) 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 subscalc). Patients rated their perception of knee instability 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.