Mechanisms underlying quadriceps weakness in knee osteoarthritis

Abstract

Purpose: To identify determinants of quadriceps weakness among persons with end-stage knee osteoarthritis (OA).

Methods: One-hundred twenty-three individuals (mean age 64.9 +/- 8.5 yr) with Kellgren/Lawrence grade IV knee OA participated. Quadriceps strength (MVIC) and volitional muscle activation (CAR) were measured using a burst superimposition test. Muscle composition (lean muscle cross-sectional area (LMCSA) and fat CSA (FCSA)) were quantified using magnetic resonance imaging. Specific strength (MVIC/LMCSA) was computed. Interlimb differences were analyzed using paired-sample t-tests. Regression analysis was applied to identify determinants of MVIC. An alpha level of 0.05 was adopted.

Results: The OA limb was significantly weaker, had lower CAR, and had smaller LMCSA than the contralateral limb. CAR explained 17% of the variance in the contralateral limb's MVIC compared with 40% in the OA limb. LMCSA explained 41% of the variance in the contralateral limb's MVIC compared with 27% in the OA limb.

Conclusion: Both reduced CAR and LMCSA contribute to muscle weakness in persons with knee OA. Similar to healthy elders, the best predictor of strength in the contralateral, nondiseased limb was largely determined by LMCSA, whereas CAR was found to be the primary determinant of strength in the OA limb. Deficits in CAR may undermine the effectiveness of volitional strengthening programs in targeting quadriceps weakness in the OA population.

Figures

FIGURE 1

Muscle identification of the quadriceps femoris muscle group on magnetic resonance image. The OA limb is on the left, and the contralateral, nondiseased limb is on the right. RF, rectus femoris; VL, vastus lateralis; VM, vastus medialis; VI, vastus intermedius.

FIGURE 2

The influence of central activation ratio (CAR) on quadriceps femoris muscle strength (MVIC). The equation shows the relationship between CAR and MVIC, and the line represents the line of best fit from the results of the exponential regression analysis. The y-axis is presented in Newtons. A, Contribution of CAR to the contralateral, nondiseased limb's quadriceps stirength. B, Contribution of CAR to the OA limb's quadriceps strength.

FIGURE 3

The influence of lean muscle cross-sectional area (LMCSA) on Quadriceps femoris muscle strength (MVIC). The equation shows the relationship between LMCSA and MVIC, and the fine represents the line of best fit from the results of the linear regression analysis. The y-axis is presented in Newtons, and the x-axis is presented in centimeters squared. A, Contribution of LMCSA to the contralateril, nondiseased limb's quadriceps strength. B, Contribution of LMCSA to the OA limb's quadriceps strength.