Side differences of thigh muscle cross-sectional areas and maximal isometric muscle force in bilateral knees with the same radiographic disease stage, but unilateral frequent pain - data from the osteoarthritis initiative.

OBJECTIVE: To determine whether anatomical thigh muscle cross-sectional areas (MCSAs) and strength differ between osteoarthritis (OA) knees with frequent pain compared with contra-lateral knees without pain, and to examine the correlation between MCSAs and strength in painful vs painless knees.
METHODS: Forty-eight subjects (31 women; 17 men; age 45-78 years) were drawn from 4,796 Osteoarthritis Initiative (OAI) participants, in whom both knees displayed the same radiographic stage (KLG2 or 3), one with frequent pain (most days of the month within the past 12 months) and the contra-lateral one without pain. Axial MR images were used to determine MCSAs of extensors, flexors and adductors at 35% femoral length (distal to proximal) and in two adjacent 5 mm images. Maximal isometric extensor and flexor forces were used as provided from the OAI database.
RESULTS: Painful knees showed 5.2% lower extensor MCSAs (P=0.00003; paired t-test), and 7.8% lower maximal extensor muscle forces (P=0.003) than contra-lateral painless knees. There were no significant differences in flexor forces, or flexor and adductor MCSAs (P>0.39). Correlations between force and MCSAs were similar in painful and painless OA knees (0.44<r<0.66).
CONCLUSIONS: Knees with frequent pain demonstrate lower MCSAs and force of the quadriceps (but not of other thigh muscles) compared with contra-lateral knees without knee pain with the same radiographic stage. Frequent pain does not appear to affect the correlations between MCSAs and strength in OA knees. The findings suggest that quadriceps strengthening exercise may be useful in treating symptomatic knee OA.