Outcomes of Iso-Elastic Acetabular Cup in Primary Total Hip Arthroplasty with 5-Year Minimum Follow-Up: A Systematic Review

Background: Long-term survivorship in total hip arthroplasty (THA) is influenced by implant stability and stress distribution to surrounding bone. Isoelastic acetabular components are monoblock polyethylene cups with a low elastic modulus, which were developed to reduce stress shielding and enhance periacetabular bone preservation. This systematic review aimed to evaluate the mid- to long-term clinical outcomes, wear rate, and survivorship of isoelastic cups in primary THA with a minimum follow-up of five years. Materials and methods: A systematic literature search was performed in April 2025 across PubMed, Embase, Cochrane Library, and Google Scholar following PRISMA 2020 guidelines. Inclusion criteria comprised clinical studies on isoelastic acetabular cups in primary THA with a minimum of five years of follow-up. Data on survivorship, complications, clinical outcomes, wear, and radiological performance were extracted and analyzed. Risk of bias in each study was assessed through the Newcastle–Ottawa Scale (NOS) for observational studies and the Cochrane Risk of Bias 2 (RoB 2) tool for randomized controlled trials. Results: Twelve studies, encompassing 1491 hips, met the inclusion criteria. Mean follow-up was 8.1 years. Overall implant survival rate ranged from 82.7% to 100%. Mean Harris Hip Score was 92.6, with low reported pain and high satisfaction. Mean annual wear was 0.05 mm/year. Vitamin E-infused highly cross-linked polyethylene (VEHXLPE) cups demonstrated lower femoral head penetration compared to UHMWPE. A randomized trial showed reduced bone loss in the polar region with isoelastic cups versus modular titanium cups (4.9% versus 15.9%, p = 0.005). Complication and revision rates were low, though heterogeneity in cup positioning reporting and variable follow-up durations were noted. Conclusions: Isoelastic acetabular components demonstrate excellent survivorship, low wear rates, and favorable clinical outcomes at mid- to long-term follow-up. High-quality, long-term comparative studies are needed to confirm these findings across broader patient populations.