RADIOGRAPHIC STUDY OF OSTEOINTEGRATION IN HYDROXYAPATITE-COATED TOTAL HIP PROSTHESES

Abstract

Introduction and Objectives: The goal of this study is to document radiographic changes occurring in patients with hydroxyapatite(HA)-coated total hip prostheses (THP).

Materials and Methods: From May 1990 to May 1993, 60 THP with complete (femoral and acetabular) HA-coating were implanted in 59 patients. Of these 59 patients, 36 were male and 23 female. Average age was 69.26 years. A retrospective study of these patients was done, with an average follow-up time of 11 years. Radiological follow-up was done at 1 month, 3 months, 6 months, 1 year, and annually thereafter. Available imaging methods included conventional radiography, direct digital radiography, digital processing, CT scan, bone scintigra-phy, and tomodensitometry. We used the first 3 of these techniques. The acetabular cup and femoral stem have been divided based on DeLee-Charnley zones (cup) and Gruen zones (femur). The following variables were tracked for the acetabular component: subchondral sclerosis, radiolucent lines, resorption, remodeling, and the appearance of osteolyic lesions. For the femoral component, the following were tracked: radiolucent lines, calcar resorption, periprosthetic cortical thickness, appearance and progression of the pedestal, appearance of osteo-lytic lesions, new intramedullary bone formation, and state of cancellous bone, with particular emphasis on periprosthetic trabeculation. We also assessed prosthetic positioning (normal, varus, valgus), angle of the acetabular component, changes in the polyethylene, and heterotopic ossification (Brooker’s classification). Radiographic studies were performed by 2 independent observers, blinded as to the clinical situation.

Results: Of the 60 THP with HA coating in our study, 5 could not be reviewed due to incorrect personal data on their clinical records, and 6 were deceased. With the cups, DeLee-Charnley zone 1 showed bone remodeling with frequent sclerotic changes, and zone 3 showed radiolucent lines of less than 1 mm. Femoral stems had a typical pattern of poor endosteal apposition around Gruen’s zone 6. Calcar remodeling was slowly progressive, with thinning of the cortex. Minimal resorption of the femoral neck was also observed. A periosteal reaction was noted in eccentrically loaded stems. Pedestals were common and did not seem to reflect loosening of the prosthesis in our data. Image digitalisation permitted the examination of newly-formed trabeculae, particularly in Gruen’s zones 2–3 and 5–6, which appeared at 3 months.

Discussion and Conclusions: Radiographic progression in most of the patients with THP with HA coating was satisfactory. Digitalisation of radiographic images permitted better visualization of changes occurring at the bone-prosthesis interface.