Aberrations in the control of quadriceps muscle force in patients with knee osteoarthritis

Objective. To characterize the distribution of error in knee joint proprioception, quadriceps force accuracy and steadiness, and muscle strength in patients with knee osteoarthritis (OA). Special attention was paid to eccentric strength. Methods. We compared knee OA patients (n = 20: 15 women, 5 men) with age- and sex-matched, symptom-free adults. Knee pain and mobility were assessed with standard tests. Knee joint proprioception was measured with a repositioning test. Quadriceps force accuracy and steadiness were determined during a force target-tracking task. Maximal voluntary quadriceps force was measured during eccentric, isometric, and concentric contractions. Results. OA patients had knee pain, needed 67% more time to complete 4 functional tasks, and produced 82% more proprioception errors (all P < 0.05). About 80% of this error was due to overshooting the target and 68% of the overshooting error occurred at 2 of the 5 least flexed knee joint positions. OA patients had 89% more errors in accurately matching target forces during submaximal quadriceps contractions and in the same tasks, OA patients also produced these forces with 155% more variability (all P < 0.05). OA patients had especially weakened ability to produce maximal voluntary eccentric strength. Conclusion. Quadriceps dysfunction in knee OA includes impaired proprioception, especially in the more extended knee joint positions; impaired ability to accurately and steadily control submaximal force; and impaired eccentric strength. These results have implications for designing exercise and rehabilitation programs for patients with knee OA.