Introduction: In the last years, the use of second generation cementless anatomical stems has generated an increasing interest in primary total hip arthroplasty. They are believed to offer long term stability through appropriate stress transfer and bone remodelling in the proximal femur. We conducted a monocentric prospective study on a homogeneous series of total hip replacements performed with a cementless anatomic, hydroxyapatite-coated stem. The purpose of the study was to evaluate the contribution of this implant in terms of clinical and radiological results at a minimum 5-year follow-up.

Material and Methods: The continuous homogeneous series included 176 THA performed between September 1997 and December 1998 by a single surgeon with the same implant system (SPS femoral stem and Hilock acetabular cup, Symbios Orthopédie SA). Indications were restricted to primary or secondary degenerative hip diseases. Revisions were excluded. Patients were reviewed for clinical performance (Harris hip score), satisfaction, and radiological outcome. The radiological analysis (implant migration, Ara and Engh scores, Brooker classification) was performed by an independent surgeon unaware of the clinical performance outcome. The survival curve was determined with the Kaplan-Meier method at 95% confidence interval, using exclusively implant revision as the criteria for failure.

Results: The follow-up rate in the series was 93.2%. The five-year implant survival was 98.8%. Two revisions were recorded: one for early instability due to excessive joint laxity after surgery, one due to recurrent dislocation following improper cup positioning during surgery. The clinical improvement was obvious, as the Harris hip score improved significantly (p< 0.0001) from 32.9±1.2 preoperatively to 93.1±0.8 at five years follow-up. Pain was the item exhibiting the largest improvement with only 10.2% of patients complaining of mild pain at last follow-up. The radiological analysis revealed a high stability of the femoral implant with Ara and Engh scores reaching 5.0±0.2 and 20.7±0.5 respectively. The migration remained low at 2.4 mm ±0.3 (p=0.02) and had no incidence on the clinical outcome. Heterotopic ossifications at various grades were observed in a large proportion of patients (65.1%). The polyethylene wear rate was 0.075 mm/yr in the series, below most values commonly reported for Ø28mm PE inserts.

Discussion: The survival rate of the SPS stem is comparable with that of other published series at same follow-up. Both the stem and cup implants used provided good clinical and radiological results at five years. The objectives of good integration and stability of the cementless anatomical stem appeared to be met, despite a significant rate of heterotopic ossifications. The excellent clinical and radiological results recorded at five years should be confirmed at longer follow-up.