Varus–valgus laxity and passive stiffness in medial knee osteoarthritis

OBJECTIVE: To compare differences in knee varus and valgus angular laxity and passive mechanical stiffness between asymptomatic knees and those with mild, moderate, and severe knee osteoarthritis (OA). METHODS: A total of 127 participants with symptomatic medial tibiofemoral OA and 32 asymptomatic controls participated. OA knees were stratified according to radiographic severity. Varus-valgus laxity was evaluated using a customized dynamometer, providing continuous measurement of varus-valgus joint angle and torque. The following indices were calculated: 1) varus, valgus, and total angular laxity, 2) end-range varus and valgus stiffness, and 3) midrange stiffness. RESULTS: There was no difference in varus, valgus, and total angular laxity, or varus and valgus end-range stiffness between the groups (P > 0.05 for all). The OA groups were less stiff in the midrange compared with the controls (P = 0.004-0.043). CONCLUSION: The absence of differences in total angular laxity is contrary to previous findings, and may be associated with the failure of previous work to account for body size effects. Less midrange stiffness in OA participants compared with controls may indicate less rotational support provided by passive joint structures in knee OA within the functionally important range. The role of passive varus-valgus stiffness in disease onset and progression is worthy of further investigation.