Bridging the Compatibility Gap in Revision Hip Arthroplasty with 14/16 Tapers: Long-Term Outcomes of the Bioball™ System

Purpose: Revision total hip arthroplasty (RTHA) in the presence of a well-fixed femoral stem carries substantial risk and morbidity, as stem removal often leads to bone loss, prolonged operative time, and increased blood loss. This issue is particularly relevant for older implants featuring a 14/16 taper, which are no longer compatible with most modern femoral heads. The Bioball™ System (Merete Medical, Germany), a modular head–neck adapter, provides a solution that enables acetabular or head-only revision while preserving the existing femoral stem. This study aimed to evaluate the long-term clinical and radiological outcomes of revision THA procedures using the Bioball™ System in patients with 14/16 femoral tapers. Methods: This retrospective study analyzed 1039 RTHAs performed at our center between 2008 and 2020. 38 patients (23 women, 15 men; mean age 73.5 years) were finally included in the study. All procedures were performed in the presence of a well-fixed femoral stem with a 14/16 taper. Revisions were limited to exchange of the acetabular component, liner, or both using the Bioball™ System, thus avoiding femoral stem removal. The primary reason for revision surgery in the study group was acetabular cup loosening (n=29, 76.31%), while only the liner was replaced in 9 patients (23.69%). Clinical evaluation included the Merle d’Aubigné and Postel score (modified by Charnley), and radiological analysis assessed component fixation, migration, and signs of loosening. The mean follow-up period was 3082 days (8.44 years; SD 1041.5; Me 2872). Results: In 29 patients (76.3%), both the acetabular component and liner were replaced, while in 9 patients (23.7%) only the liner and head were exchanged. The most commonly used adapter lengths were 2XL (+10.5 mm, 28.95%), 5XL (+21 mm, 21.05%), 3XL (+14 mm, 18.42%), and 4XL (+17.5 mm, 15.79%); shorter sizes (M, L, XL) were applied less frequently. A 7.5° offset adapter was used in 57.9% of cases to optimize offset and anteversion, and 32 mm heads were employed in 71.05% of revisions. The modified Merle d’Aubigné and Postel (MAP) score improved by a mean of 5.7 points (p < 0.05), with good outcomes in 36.84% and fair in 63.16% of patients. Pain intensity on the VAS scale decreased from 7.4 to 2.6 (p < 0.05). Furthermore, until the final day of the follow-up period i.e. June 30, 2025, no signs of prosthesis loosening were noted in any of the patients included in the study. The Modified MAP score was distributed the same between the different procedure types (p=0.404). Conclusion: The Bioball™ System enables restoration of hip stability and offset without removing a well-fixed femoral stem, thereby reducing surgical invasiveness, blood loss, and procedure-related risks. It provides an effective solution for revisions involving older 14/16 tapers, where conventional 12/14 heads are incompatible, and demonstrates favorable long-term functional and radiological outcomes. Further studies are warranted to confirm its broader applicability in complex revision THA.