Long-term results of the ABG-1 hydroxyapatite coated total hip arthroplasty: analysis of 111 cases with a minimum follow-up of 10 years.

INTRODUCTION: Medium-term studies of ABG-1 cementless total hip arthroplasty have shown favorable functional results with excellent femoral component fixation but an abnormally high rate of periacetabular component osteolysis, which may require early revision.

HYPOTHESIS: The periacetabular osteolysis rate increases with time with the ABG-1 implant, leading to a high revision rate.

OBJECTIVE: The objective of this study was to test this hypothesis with a minimum follow-up of 10 years and evaluate the progression of periacetabular osteolysis and its consequences on implant fixation.

MATERIAL AND METHODS: A continuous series of 111 ABG-1 cementless prostheses implanted by a single operator with a theoretical minimum follow-up of 10 years. Seventy-five implants were analyzed with a mean follow-up of 13 years. All the prostheses had been implanted via a posterolateral approach and consisted of a 28 mm cup matching a head in zirconia and an antidislocation rim design high-density polyethylene insert.

RESULTS: Twelve cups were revised because of progressive retroacetabular osteolysis. The revisions were performed systematically although there was no pain or gross cup loosening. The revisions included resection of the granuloma, cavity filling with morselized bone grafts, and implantation of new uncemented ABG-2 cups in eight cases or cemented cups associated with a support ring in the four other cases. Thirty-two (48.5%) of the cups still in place at the end of the follow-up evaluation presented moderate and asymptomatic radiographic osteolysis, inciting close subsequent observation. No predictive factor of osteolysis onset was identified (age, body mass index, polyethylene wear, or cup orientation). None of the femoral stems was changed because of osteolysis: the only two femoral revisions resulted from periprosthetic fracture and one case of bipolar loosening. The femoral osteolysis images were small and all limited to zones 7a (18.8% of cases), 1a, and 1b (65.2% of cases). The overall survival rate of the series at 13 years of follow-up was 80.5%; the cup survival rate was 83.2%; the femoral implant, 94.3%; and failure of the femoral stem secondary to aseptic loosening was only 1.3%.

DISCUSSION, CONCLUSION: This long-term study confirms the high frequency of retroacetabular osteolysis of ABG-1 prostheses surpassing the osteolysis rate of other uncemented cups with a polyethylene insert. The absence of predictive criteria of osteolysis occurrence and the lack of symptoms warrants periodic follow-up of patients with ABG-1 cups and, if necessary, early repair of bone stock loss with grafts combined with acetabular cup revision. This procedure remains simple as long as performed before the onset of massive bone destruction, confirming the proposed revisions in this series were judicious. This study also confirms the excellent long-term fixation of the ABG-1 femoral stems derived from the osteointegration and proximal seal around the hydroxyapatite coating.