REVIEW OF 192 METAL-BACKED HIP PROSTHESES AT SEVEN YEARS

Abstract

Purpose: We were confronted with four cases of major loosening with migration of the metal-backed implant and acetabular osteolysis at seven years follow-up. We thus conducted a retrospective clinical and radiological analysis of our 192 prosthesis of this type implanted in 1993.

Material and methods: The clinical results were analysed using the Postel Merle d’Aubigné score (PMA). Radiographic wear was measured on the AP views without loading according to the Charnley method. Osteolysis was determined on the AP view using the De Lee and Charnley criteria. Certain files also had a scintigraphy or a CT scan performed to search for bone lysis. Osteolysis and femoral loosening were studied on the AP and lateral views. In agreement with the literature, wear of 0.1 mm/year was considered normal for these cemented prostheses and 0.15 mm/year for metal-backed cups.

Results: For the femoral component, there were two cases of loosening with massive osteolysis with a sanded titanium inserted with cement. None of the patients, with a cemented or non-cemented prosthesis underwent revision for pain. At the acetabular level, there were no failures for primary instability. Wear was normal (mean 0.08) in 89 cases (46.5%) and excessive (mean 0.26) in 103 cases (53.5%). Significant factors for wear were: patient age, gender, and level of activity. Factors without a significant influence were: size of the acetabular cup, type of bead, patient overweight. Osteolysis was the consequence of abnormal wear since in 42% of the abnormal wear cases showed osteolysis compared with 20% when wear was less than 0.15. The same observations were made for the clinical impact as 15.5% of the worn cups were symptomatic (PMA < 4) and 18 of the 103 patients (17.5%) underwent or will undergo revision.

Conclusion: Metal-backed cups present excessive wear at mid term causing early failure by osteolysis and implant migration. There are two options: remove the polyethylene sing a new metal-on-metal combination or a ceramic-ceramic combination, or returning to the metal-polyethylene combination with a cemented cup.