Migration of cemented stem and restrictor after total hip arthroplasty: a radiostereometry study of 25 patients with Lubinus SP II stem.

The aim of this study was to investigate the migration pattern of the Lubinus SP II prosthesis stem. Migration at the stem-cement and at the bone-cement interface was assessed. Twenty-five patients were studied by radiostereometry during a period of 2 years. The migration of the head, of 2 points on the collar, of the stem tip, and also of the cement restrictor, was measured. The collar and the head were found stable at 2 years' follow-up, whereas an anterior migration occurred at the stem tip (median, 0.3 mm; 25th percentile, 0.04 mm; 75th percentile, 1.27 mm). Virtually no subsidence or axial rotation of the stems was observed. An anterior migration of the restrictor marker was also observed, compatible with a rigid sagittal plane rotation of the stem and of the cement mantle about the collar. Therefore, stem tip migration occurred at the bone-cement interface. Key words: total hip arthroplasty, anatomic stem, radiostereometry, subsidence, bone-cement interface.