Evaluation of the biomechanics of the hip following a triple osteotomy of the innominate bone.

The biomechanics of the hip joint were evaluated in seventeen patients (twenty-two hips), twelve to forty-one years old (mean, twenty-four years old), who had a triple osteotomy of the innominate bone for treatment of symptomatic dysplasia of the hip. The duration of follow-up ranged from 2.2 to 13.8 years (mean, 6.8 years). Hip load, the area of the weight-bearing surface, and stress were determined from measurements on pelvic radiographs that were made preoperatively, postoperatively, and at the time of the latest follow-up; the values were compared with those in twenty-one hips from control subjects. The Harris hip-rating system was used for clinical assessment. According to the biomechanical analysis, there was significantly less relative stress on the hip after the triple osteotomy and at the time of the latest follow-up (p < 0.001 for both) than there had been preoperatively. The decrease in stress was a direct result of a significant increase in the area of the weight-bearing surface of the hip (p < 0.001). The load on the hip was not altered significantly, with the numbers available. The functional outcome was improved substantially when the biomechanical goals were achieved. Through the application of basic biomechanical principles, we were able to demonstrate the biomechanical efficacy of a triple osteotomy of the innominate bone. We recommend the use of biomechanical analysis as an adjunct to the clinical decision-making process in the treatment of a dysplastic hip.