Gait and function after intra-articular arthrodesis of the hip in adolescents

Background: Patients who have had a hip arthrodesis have been reported to have pain in the back and the knee due to an altered gait. There is little information about the specific compensatory mechanisms that are adopted when walking. The purpose of this study was to objectively define gait adaptations after an arthrodesis of the hip and to correlate the kinematic findings with pain and other patient outcomes. Methods: Nine patients who had had an arthrodesis of the hip at an average age of thirteen years and five months (range, ten years and nine months to sixteen years and eleven months) were evaluated with gait analysis and muscle strength-testing and completed a questionnaire related to pain and function. The average duration of follow-up was eight years and ten months (range, two years and one month to thirteen years and ten months). The frequency of the postoperative visits varied. Seven patients were adults at the time of the study and were called back specifically for the study. Results: All patients had decreased cadence and step lengths. The kinematic findings included decreased dorsiflexion of the ipsilateral ankle, hyperextension of the ipsilateral knee during the stance phase, and a tendency toward increased genu valgum during gait. In normal gait, there is no genu varum or valgum during the stance phase. The patients had an average (and standard deviation) of 7 ± 4 degrees of genu valgum. Pelvic and lumbar motion in the sagittal plane was excessive in all patients. Strength-testing revealed clinically relevant weakness in the ipsilateral quadriceps in all patients, with a difference of more than 20 percent between the two extremities in six patients. The gastrocnemiussoleus muscle was stronger on the side with the fused hip in six patients. The questionnaire, designed by Harris in 1969 and completed by the patients at the time of the gait analysis, revealed back pain in seven patients. The questionnaire was administered only once. The functional outcome as measured with use of the same questionnaire worsened as the duration of follow-up increased. Conclusions: The gait analysis showed excessive motion in the lumbar spine and the ipsilateral knee in all nine patients. This abnormal motion led to pain as the duration of follow-up increased, and all patients who had been followed for four or more years after the arthrodesis complained of back pain. We hypothesized that excessive motion for an extended duration can lead to back pain. The preferred position of the hip for the arthrodesis was 20 to 25 degrees of flexion, neutral abduction-adduction, and neutral rotation.