Cementless calcar-guided short stems: 24-month clinical outcomes and migration analysis

Calcar-guided short stems aim to preserve proximal bone stock and reconstruct individual anatomy, but reduced diaphyseal anchorage raises concerns regarding initial stability. This prospective cohort study evaluated migration of the A2 calcar-guided short stem using high-precision radiostereometric analysis (RSA). Sixty patients (mean age 57.8 years) undergoing primary total hip arthroplasty were enrolled. Marker-based RSA was performed at baseline and at predefined intervals up to 24 months. The primary endpoint was axial subsidence (Ty) at 2 years. Secondary outcomes included three-dimensional migration and clinical scores, including the Harris Hip Score (HHS). Longitudinal migration was analysed using linear mixed models. At 24 months, mean axial subsidence (Ty) was - 0.29 mm (95% CI - 0.53 to - 0.06). Mean total translation (Txyz) was 0.74 mm (95% CI 0.50 to 0.98), and mean retroversion (Ry) was 2.31° (95% CI 1.84° to 2.79°). Migration occurred predominantly in the early postoperative phase, followed by stabilisation. Two stems (3.3%) required revision during follow-up, one due to undersizing with insufficient cortical contact and one after a traumatic fall. The remaining implants demonstrated stable fixation. Mean HHS exceeded 95 at 24 months. The A2 calcar-guided short stem showed early settling followed by stable fixation, with excellent clinical outcomes at 2 years.