Strength and voluntary activation of the quadriceps femoris muscle at different severities of osteoarthritic knee joint damage

Objective: Improvements of quadriceps motor deficits represent a major therapeutical target in knee osteoarthritis (OA). In the present study, we investigated changes in quadriceps function at different stages of osteoarthritic cartilage damage.

Methods: Measurements of quadriceps voluntary activation (VA) and maximum voluntary contraction (MVC) were performed by a twitch interpolation technique and the total muscular capacity (TMC) was calculated as the ratio of MVC and VA. We assessed 68 patients (56.7 ± 9.5 years) with stage II and 154 patients (65.6 ± 6.0 years) with stage IV chondropathy. As controls, we used 85 age related healthy subjects (58.1 ± 8.7 years).

Results: While TMC was significantly lower in stage IV (90.6 ± 43.7 N m) than in stage II chondropathy (109.6 ± 51.0) there were no differences in the MVCs between both groups. Quadriceps VA was even higher in stage IV (77.2 ± 13.2%) than in stage II chondropathy (70.8 ± 16.0%). In the controls, MVC, VA and TMC were significantly higher than in both OA groups.

Conclusion: We assume that a decrease of TMC might occur within the course of OA and, in consequence, VA increases to maintain quadriceps MVC.