Prospective clinical and radiostereometric analysis of the Fitmore short-stem total hip arthroplasty

Uncemented short, curved femoral stems may help save proximal bone stock during total hip arthroplasty (THA) and facilitate insertion in minimal invasive surgery. The aim of this 2 year, prospective, single-center study was to examine the stability and migration of the Fitmore (A (R)) stem in THA using model-based radiostereometric analysis (RSA), and thus predict the implant's long-term survival. In addition, we evaluated the stem's clinical performance using standard clinical measures. We conducted a prospective cohort study of 34 THA patients who received the short Fitmore Hip Stem (Zimmer, Winterthur, Switzerland). At 3, 6, 12 and 24 months postoperatively, the patients underwent clinical evaluation and radiostereometric analysis (RSA) to measure stem migration. RSA analysis revealed a mean subsidence of -0.39 mm (95 % CI -0.60 to -0.18) at 3 months with no further migration after 2 years. Mean internal rotation along the longitudinal axis was 1.09A degrees (95 % CI 0.52-1.66) at 2 years, versus 0.85A degrees (95 % CI 0.44-1.26) at 3 months. The Harris hip score improved from 60 (range 30-80) preoperatively to 99 (range 83-100) after 2 years. Three patients underwent revision due to deep infection, non-specific thigh pain and aseptic loosening in one case. We conclude that the Fitmore Hip Stem stabilizes after 3 months and achieves good short-term clinical results in most cases.