Migration pattern of a short uncemented stem with or without collar: a randomised RSA-study with 2 years follow-up

Background: There is an increasing interest in shorter, proximally loading, uncemented femoral stems. The aim of this study was to evaluate a new short stem type, its design based on a well-proven precursor, but with several new design features to facilitate easier insertion and possible preservation of proximal bone stock. It is available with or without a collar. Methods: The study includes 50 patients with primary osteoarthritis, mean age 59 (range 36–75) years, randomised to receive either the collar-fitted or the collarless stem. The patients underwent repeated radiostereometry (RSA) examinations (0, 0.5, 3, 12, 24 months), conventional radiography and filled out both hip-specific (HOOS) and general health (EQ-5D) questionnaires. Results: There was no statistically significant difference between the collared and collarless stems regarding migration and clinical outcome. Both stem types exhibit a similar pattern of initial subsidence (collared 0.63 mm vs. collarless 0.75 mm [p = 0.50]) and retroversion (collared 0.71° vs. collarless 0.97° [p = 0.36]) up to 3 months followed by stabilisation, in similarity with its precursors, suggesting good osseointegration. No stem has been revised or considered loose. Conclusions: The new design features, including shortening the stem, do not compromise migration pattern or osseointegration, regardless collar or not.