Abstract
Introduction
Modular dual mobility (MDM) prostheses are increasingly utilized for total hip arthroplasty (THA) to mitigate the risk of postoperative instability in high risk patients. Short-term reports on clinical outcomes are favorable but there are few studies on young active patients. This study quantified proximal femoral stress shielding and metal ion release in MDM combined with modern cementless stem design in young active patients.
Methods
This was a prospective study of patients between 18 and 65 years of age, with a body mass index (BMI) < 35 kg/m2 and University of California at Los Angeles (UCLA) activity score > 6, who received a modular cobalt-chromium acetabular liner, highly crosslinked polyethylene mobile bearing, and cementless titanium femoral stem for their primary THA. DEXA scans were performed at 6 weeks postoperatively as a baseline, then again at 6 months, 1 year, 2 years and 5 years postoperatively as were metal ions.
Results
A total of 43 patients (30 male, 13 female; mean age 52.6 years (sd 6.5)) were enrolled. At the time of analysis, 14 patients had completed DEXA scans at 5 years postoperatively. There was no significant loss of proximal femoral bone mineral density in Gruen Zones 1–7 or acetabular bone mineral density in Gruen Zones 1–6 between 6 weeks and 5 years postoperatively (p > 0.05 for each zone). Sixteen patients had metal ions at 5yrs. Cobalt levels averaged .07 ppb (range .012 – .451) and chromium levels averaged 0.24 ppb (range .092 – .883)
Conclusion
At a minimum 5 years follow up, MDM with a modern cementless stem demonstrated minimal stress shielding and no concerning metal ion release in young active patients.
