A case study of gait compensations for hip muscle weakness in idiopathic inflammatory myopathy

Abstract

Background: The purpose of this case series was to quantify different strategies used to compensate in gait for hip muscle weakness.

Methods: An instrumented gait analysis was performed of three females diagnosed with idiopathic inflammatory myopathies and compared to a healthy unimpaired subject. Lower extremity joint moments obtained from the gait analysis were used to drive an induced acceleration model which determined each moment's contribution to upright support, forward progression, and hip joint acceleration.

Findings: Results showed that after midstance, the ankle plantar flexors normally provide upright support and forward progression while producing hip extension acceleration. In normal gait, the hip flexors eccentrically resist hip extension, but the hip flexor muscles of the impaired subjects (S1-3) were too weak to control extension. Instead S1-3 altered joint positions and muscle function to produce forward progression while minimizing hip extension acceleration. S1 increased knee flexion angle to decrease the hip extension effect of the ankle plantar flexors. S2 and S3 used either a knee flexor moment or gravity to produce forward progression, which had the advantage of accelerating the hip into flexion rather than extension, and decreased the demand on the hip flexors.

Interpretation: Results showed how gait compensations for hip muscle weakness can produce independent (i.e. successful) ambulation, although at a reduced speed as compared to normal gait. Knowledge of these successful strategies can assist the rehabilitation of patients with hip muscle weakness who are unable to ambulate and potentially be used to reduce their disability.

Figure 1

Results from the gait analysis as a percent of stance phase for the 3 subjects with weakness (S1–S3) and the unimpaired subject (NL). Joint angle is in the top row and flexion angles are positive. Joint moments are in the bottom row and internal extensor moments are positive. Ground reaction forces are shown on the far right, with anterior on the top, and vertical (upward) on the bottom being positive. Results represent the mean (and standard deviation, gray lines) of 4 repeated trials per subject, except S3 contributed only 3 trials. The large tick mark on the horizontal axis is at 66% of stance phase and corresponds to the average time at which the induced acceleration analysis was performed.

Figure 2

Input to and results from the induced acceleration analysis for the 3 subjects with weakness (S1–S3) and the unimpaired subject (NL). From top to bottom, graphic showing input joint positions, input joint moments (internal extensor moments are positive), output vertical GRF (up is positive), A/P GRF (anterior is positive), and hip acceleration (flexion is positive). Output bar graphs show how much each input joint moment or gravity (passive source) contributed to producing upright support, forward progression, or hip joint acceleration.