S-ROM prosthesis in Primary Total Hip Arthroplasty: a Mean Follow up of 8.5 Years

Introduction: The S-ROM® femoral prosthesis was developed to provide proximal modularity in total hip arthroplasty (THA). . This prosthesis allows for significant intra operative “customization” making it an option for femoral deformities or mismatch.

The purpose of this study is to report on our clinical and radiologic mean 8.5 year follow up results in a cohort of patients that received the S-ROM femoral component.

Methods: Between February 2000 and September 2016, 186 cementless THAs were performed in 140 patients (36 men and 104 women) using the S-ROM femoral component. The average age at time of surgery was 45 (13-77yrs). Primary diagnoses were DDH (84) , osteoarthrosis (48), rheumatoid arthritis, (17), juvenile rheumatoid arthritis (13), osteonecrosis (9) and 15 other causes. Clinical results were assessed by Harris Hip Score (HHS) and The University of California at Los Angeles score (UCLA). Radiological results were assessed by serial X-rays.

Results: The average follow-up was 8.5 years (range: 2 to 15.5 years). Twenty-three hips (in 17 patients) were lost to follow up. The mean HHS and UCLA scores significantly improved (p<0.0001) at the last follow up from 47 and 4 pre-operatively to 85 and 6 respectively. Of the 163 stems available for evaluation, stable stem fixation was present in 152 hips and 3 hips were fibrous unstable . A total of eight hips (5%) were revised: two for aseptic loosening, two for stem fracture, two for polyethylene wear, one for infection and one metal-on-metal THA was revised for pseudotumor. Kaplan-Meier survival analysis showed a survival rate of 93 % at 15 years with revision for any cause and a survival rate of 97 % at 15 years with revision for stem-related causes only.

Conclusion:

Of the entire cohort of 163 hips, only four cases (2.4%) required revision surgery for stem-related failure. Howver modularity is a mixed blessing as he two cases of stem fracture were directly related to modularity. Retrieval analysis revealed that crevice corrosion at the stem-sleeve interval was responsible for the failure of the two relatively small diameter stems (8mm and 9mm) in patients with elevated BMIs. Both cases of aseptic loosening occurred with undersized stems.

The excellent results reported in this cohort of relatively young patients are comparable to those in the literature. The S-ROM stem remains a viable option in the armamentarium of femoral reconstruction for THA.