Anteroposterior and varus–valgus laxity of the knee increase after stair climbing in patients with mild osteoarthritis

The aim of this study was to measure exercise-induced changes in knee joint laxity in patients with knee osteoarthritis (OA). The study subjects were 46 female patients with OA and 22 age- and sex-matched normal controls. Radiographs of the knee were taken in all subjects, and the disease severity was graded according to the Kellgren and Lawrence (K–L) grading system. The K–L grade of the control subjects (non-OA group) was 0–1. The OA patients were divided into those with mild OA (K–L grade 2, n = 20) and advanced OA (K–L grade 3–4, n = 26). The subject climbed up and down 8 steps on a staircase apparatus over a period of 10 min. The anteroposterior (A–P) translation was measured with KT2000 arthrometer, and varus–valgus (V–V) rotation was measured on stress radiographs before and after the stair climbing. The Δchange in A–P translation after the exercise was significantly larger in mild OA group than other groups (P < 0.005). The Δchange in V–V rotation after exercise was significantly larger in mild and advanced OA groups than the control (P < 0.003). There were no significant differences in A–P laxity and V–V laxity before exercise among the non-OA, mild OA and advanced OA groups. Exercise resulted in significant changes in A–P knee joint laxity in patients with mild OA relative to the control. The results suggest that daily physical activities (e.g., knee bending or squatting) play a role in the development of knee laxity, particularly in patients with mild OA, and that progression of knee OA seems to correlate with increments of A–P knee joint laxity.