Knee extensor and flexor muscle power explains stair ascension time in patients with unilateral late-stage knee osteoarthritis: a cross-sectional study.

OBJECTIVES

To determine the extent of asymmetrical deficits in knee extensor and flexor muscles, and to examine whether asymmetrical muscle deficits are associated with mobility limitations in persons with late-stage knee osteoarthritis (OA).

DESIGN

Cross-sectional.

SETTING

Research laboratory.

PARTICIPANTS

A clinical sample (N=56; age range, 50-75y) of eligible persons with late-stage knee OA awaiting knee replacement.

INTERVENTIONS: Not applicable.

MAIN OUTCOME MEASURES: Knee extensor and flexor power and torque assessed isokinetically; thigh muscle cross-sectional area (CSA) assessed by computed tomography; mobility limitation assessed by walking speed and stair ascension time; and pain assessed with the Western Ontario and McMaster Universities Osteoarthritis Index questionnaire.

RESULTS

The asymmetrical deficits in knee extensor and flexor power and torque were between 18% and 29% (P<.001). Regarding the thigh muscle CSA, the asymmetrical deficit was 4% (P<.001). Larger asymmetrical knee extensor power deficits and weaker knee extensor and flexor power on the contralateral side were associated with slower stair ascension times. Moreover, weaker knee extensor and flexor power on the ipsilateral side were associated with slower stair ascension times. Greater knee pain in the OA joint was independently associated with slower stair ascending time in both models.

CONCLUSIONS

The knee extensor and flexor muscle power of both the ipsilateral and contralateral sides and the pain in the OA knee were independently associated with stair ascension times. These results highlight the importance of assessing muscle power on both sides and knee pain in the prevention of mobility limitations in patients with knee OA.