Effect of foot-progression angle on hip joint moments during gait

Loosening has emerged as the most serious long-term complication of total hip replacement and torsional loading of the femoral implant has been implicated as a possible cause. In an effort to explore a strategy for minimizing this risk, the following hypothesis was tested: the foot-progression angle has a significant effect on the resultant hip moments, and particularly the internal-external rotation moment, during level walking. Twelve normal subjects performed a total of nine trials: three in which they walked normally with the right foot pointing approximately straight ahead; three in which they were told to walk with the foot internally rotated approximately 30°; and three in which the foot was externally rotated about 30°. The inverse dynamics approach was used to integrate the body segment parameter, kinematic and force plate data, and to solve for the resultant moment at the right hip joint. In all three conditions—foot straight, foot in, and foot out—the subjects walked at the same average speed of 1.5 (± 0.3) m s−1. For the flexion-extension moment (where the maximum flexion moment of 95 Nm was in good agreement with other published data), there was no significant difference between the three foot orientation conditions. For the abduction-adduction moment, the foot straight condition exhibited the classic double peak pattern with a maximum abductor moment of 57 Nm, and there was no statistically significant difference between the three curves. Although the three curves for the internal-external rotation moment were similar in shape, the foot out condition resulted in a statistically significant (p< 0.05) reduction, from 10 to 5 Nm, in the external rotation moment at 40% of the gait cycle. The hypothesis was therefore shown to hold true for the internal-external rotation moment, but it is not certain whether this reduction of about 5 Nm has any clinical significance. The findings do suggest that foot progression and other strategies to reduce torsional loading on the femoral implant could be explored with patients who have undergone total hip arthroplasty.