Subsidence Pattern of a Cementless Straight Titanium Alloy Femoral Stem – A Radiographic Study with EBRA-FCA

EBRA (Ein Bild Roentgen Analyse) is a computer-aided algorithm to assess migration of endoprosthetic components. Stem subsidence is measured in comparable radiographs, as defined by the software. Recent studies showed an improved accuracy of EBRA-FCA as compared to standard methods. For the BiCONTACT^® cementless femoral component, a prospective follow-up study of 250 cases has provided excellent results, with a survival rate of 97.1% after 11 years. For this migration study 93 hips with a complete radiographic follow-up (>10 x-rays) over 120 months were included. Seventy-one stems were be measured; in 22 stems the measurement was impossible due to heterotopic ossification. Thirty-two hips (45.1%) showed initial subsidence within the first 24 months but no later, and 11 hips (15.5%) had a late onset of subsidence. In nine hips (12.7%) continuous sinking could be found. Nineteen hips (26.8%) had irregular patterns of migration. In 31.0% the overall migration was between 0.5–1mm after 120 months. Six stems (8.5%) had an absolute amount of subsidence exceeding 2mm after 120 months (one more than 3 mm). The mean subsidence was 0.2mm after three months and six months, 0.3mm after 12 months and reached 0.5mm after 10 years. EBRA-FCA is a practicable method to assess migration of the femoral component. There seems to be initial subsidence for about one half of the stems but further movements are rare, which might be a sign for osseo-integration. The radiographic findings correspond to the excellent clinical performance of this stem in long-term follow-up.