Total hip arthroplasty after hip arthrodesis: functional outcomes, and mid-term survivorship integrating the fusion technique complexity score.

BACKGROUND: Conversion of hip arthrodesis to total hip arthroplasty (THA) is technically demanding because of altered anatomy, soft-tissue contractures, and long-standing biomechanical adaptations. Preoperative complexity varies widely, and contemporary data on functional recovery and complications remain limited. This study evaluates functional and radiographic outcomes after conversion THA and introduces a Fusion-to-THA Surgical Complexity Score (FTCS) to characterise preoperative difficulty and explore its association with perioperative outcomes. PATIENTS AND METHODS: We retrospectively reviewed 23 consecutive patients (16 males, 7 females; mean age 52 ± 12 years) who underwent conversion THA between 2014 and 2020, after a mean fusion duration of 22 ± 7 years. All procedures were performed through a posterior approach using cementless dual-mobility acetabular components and individualised femoral fixation. The FTCS incorporated fusion duration, soft-tissue contractures, retained hardware, leg-length discrepancy, abductor status, and acetabular distortion. Outcomes included Harris Hip Score (HHS), hip range of motion, gait, leg-length discrepancy, knee pain, and radiographic assessment using Engh and DeLee-Charnley criteria. Correlations between FTCS and perioperative parameters were analysed. RESULTS: At a mean follow-up of 6.2 years, HHS improved from 42 ± 8 to 82 ± 10 (p < 0.001). Mean hip flexion reached 85° ± 15°, gait normalised in 20 patients, and leg-length discrepancy was corrected in 21. Knee pain decreased significantly and correlated with leg-length correction (r = 0.52, p = 0.004). Higher FTCS values were associated with longer operative time and increased blood loss, representing exploratory associations within this cohort. Radiographs showed stable fixation and reliable osteointegration (mean Engh score 7.8 ± 1.2). 1 femoral stem revision and minor complications occurred, with no infections or permanent nerve injuries. CONCLUSIONS: Conversion THA after hip arthrodesis yields substantial functional recovery and durable mid-term implant stability. The FTCS represents an exploratory descriptive framework to characterise preoperative complexity; however, its clinical applicability requires further validation in larger cohorts.