Knee muscle torques of healthy adults with tibia vara: Hypothetical relationship to medial compartment knee osteoarthrosis

Background: In earlier work we noted that women with medial compartment knee osteoarthrosis and varus deformity displayed greater neuromuscular deficiencies of quadriceps muscles than those with normal tibial alignment when tested isokinetically at 90° sec ^{-1} and at 0° sec ^{-1} using an isokinetic dynamometer.

Purpose: The present purpose was to provide further insight into the potential influence of muscular factors in the development of medial compartment knee osteoarthrosis.

Methods: Because our previous findings indicated significantly greater torque generating problems at higher isokinetic speeds than lower speeds among adults with varus alignment deformities, and prior work is strongly associated with isometric test outcomes, we elected to perform quantitative measures of maximal isometric knee torques generated 0° sec ^{-1} and to compare these to validated goniometric alignment measures of the lower legs of 14 health individuals exhibiting genu varum on a single test occasion.

Results. The analyses revealed: 1) a significant inverse relationship between the right quadriceps and hamstrings muscle torque and right tibia varus measures (r=-0.59; r=-0.66), and between the left hamstrings muscle torque and left tibia vara measures (r=-0.62) (p < 0.05) when controlling for gender; 2) antagonist-agonist knee torque ratios that tended to vary inversely with the magnitude of the prevailing varus deformity; 3) the presence of asymmetric tibia vara magnitudes with greater angulations recorded for the subject's right side, regardless of limb dominance; 4) greater varus angulation deformities for both legs of the males compared to the females (p< 0.05).

Conclusions: The slope of the regression line linking the maximal knee extensor and flexor torques of healthy young adults tends to vary inversely with the degree of varus angulation as presently recorded. There may be considerable intra-individual and gender differences in the manifestation of this finding. These observations may have a bearing on the etiology and pathogenesis of uni- or bilateral medial compartmental knee joint disease in healthy adults exhibiting genu varum, hence warranting further study using more sophisticated measures and isokinetic testing at different angular velocities.