197. PRELIMINARY AND COMPARATIVE RESULTS IN A CONSECUTIVE SERIES OF 250 HIP PROSTHESES WITH A LARGE DIAMETER HEAD

Abstract

Purpose of the study: The tribologic characteristics of the metal-on-metal bearing enabled the introduction of large-diameter femoral heads on a conventional stem with the aim of improving implant stability. Our work was designed to determine whether the short-term outcomes corroborate this hypothesis and identify any specific complications.

Material and methods: This was a comparative study of two series of non-cemented total hip arthroplasties (THA) with a high-carbon content metal-on-metal bearing: 250 25 mm arthroplasties implanted from August 2001 to April 2004; 250 large-diameter arthroplasties implanted from August 2003 to December 2006. The two series were comparable regarding age, gender, BMI, aetiology, Devane and Harris scores preoperatively (r2=0.98; p< 0.001). Patients were reviewed at mean 5 years 5 months (28mm) and 3 years 1 months (large diameter).

Results: The analysis was possible for 224 implants in the 28 mm series and 242 in the large diameter series. Clinically, the Merle-d’Aubigné et Harris scores were highly comparable between the series; the activity item on the UCLA score revealed better results in the anatomic head series (6.09 versus 6.81; p< 0.0039). Regarding complications: There was one cases of implant migration in the large diameter series with preservation of the good outcome and no revision. For dislocations: anatomic head (n=1, 0.4% with revision); 28 mm head (n=7, 2.8% with four revisions). One particular case of one patient with a large diameter head presented two episodes of localised recurrent cellulitis under regular surveillance. Metal ion assays (medians): Cr.− 1.55μg/l for 28mm; 2.21μg/l for large diameter; Co. − 1.10μg/l for 28mm; 1.92μg/l for large diameter.

Discussion: Our results provide objective evidence of the improvement in the stability of the prosthesis joint and in the functional outcome, confirming the few results published to date. Conversely, while we did have less technical failures than published series, we did find significantly higher metal ion levels in the large diameter series, in contrast with prior data. The neck length being modulated with the intermediary piece, the potential corrosion might be the only cause of this difference.