Mechanisms underlying quadriceps weakness in knee osteoarthritis.
OBJECTIVE
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.


CONCLUSIONS
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.
Petterson
Stephanie C
SC
School of Health & Bioscience, University of East London, London,U.K. s.petterson@uel.ac.uk
Barrance
Peter
P
Buchanan
Thomas
T
Binder-Macleod
Stuart
S
Snyder-Mackler
Lynn
L
D000368:Aged; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D018908:Muscle Weakness; D020370:Osteoarthritis, Knee / Q000503:physiopathology*; D052097:Quadriceps Muscle / Q000502:physiology*; D012044:Regression Analysis