Intrinsic foot muscle size and associations with strength, pain and foot-related disability in people with midfoot osteoarthritis.

Background: To compare intrinsic foot muscle size between people with and without symptomatic midfoot osteoarthritis, and examine the association between muscle size and strength, pain and foot-related disability.

Methods: Twenty-three participants with symptomatic midfoot osteoarthritis and 23 age, sex and BMI matched controls were included. Intrinsic foot muscle cross-sectional area was measured using MRI. Hand-held dynamometry was used to assess foot and ankle muscle strength, and foot-related pain and disability was measured using Manchester Foot Pain & Disability Index.

Findings: Small and non-statistically significant differences were found in intrinsic foot muscle cross-sectional area between the two groups (effect sizes 0.15-0.26, p > 0.05). Muscle strength was reduced in the midfoot osteoarthritis group, with differences of 12-33% (effect sizes 0.47-1.2). In the control group, moderate positive associations) existed between foot muscle cross-sectional area and lesser digits flexor strength (r = 0.5 to 0.7, p < 0.05). Conversely, in the midfoot osteoarthritis group, negligible positive associations were found (r < 0.3, p > 0.05). Associations between foot muscle cross-sectional with and pain and disability scores in the midfoot osteoarthritis group were negligible (r < -0.3, p > 0.05).

Interpretation: Despite reductions in maximal isometric muscle strength, midfoot osteoarthritis does not appear to be associated with reduced intrinsic foot muscle cross-sectional area measured by MRI. Muscle compositional or neural factors may explain the reductions in muscle strength and variation in symptoms in people with midfoot osteoarthritis and should be investigated.