The influence of heterotopic ossification on functional status of hip joint following total hip arthroplasty

Purpose: The functional failure induced by heterotopic ossification (HO) following total hip arthroplasty (THA) was analyzed and correlated to the radiologic failure. Patients and Methods: From July 1997 to July 2001, 315 patients (345 hips) received THA indicated by a hypertrophic osteoarthritis of higher degree (Kellgren grade III, IV). ALL patients were irradiated prophylactically for prevention of HO on the evening before surgery with a 7-Gy single fraction. The patients' median age was 663 years. Radiologic failure was assessed by comparison of pre- and postoperative hip X-rays (immediately and 6 months after surgery). Analysis of radiographs was performed according to the Brooker Score. Clinical failure was appraised by measurement of passive range of motion (ROM) of the hip joint with a standard goniometer. The t-test was used for statistical analysis. Results: 281 patients (81.5%) did not develop HO. HO of Brooker grade I or II was found in 58 patients (16.8%). Six patients (1.7%) developed HO Brooker grade III or IV. There was a significant negative correlation between the degree of radiologic and clinical failure. ROM differed significantly between patients with HO Brooker grade 0, 1, 11 and patients with HO Brooker grade III, IV. Comparing the pre- and postoperative ROM, all patients with Brooker grade 0, 1 and II showed a significant improvement of flexion, internal and external rotation, abduction and adduction movement. Patients with HO Brooker grade III and IV showed no improvement of ROM in the postoperative follow-up. Conclusion: The development of HO following THA influences the physical function of the hip joint dependent on the degree of ossification. HO of Lower degree (Brooker 1, 11) does not influence the clinical outcome, whereas HO of higher degree (Brooker III, IV) reduces the function of hip arthroplasty. Therefore, the purpose of a prophylactic therapy must be to reduce HO of higher degree.