Stable migration pattern of an ultra-short anatomical uncemented hip stem: A prospective study with 2 years radiostereometric analysis follow-up

Introduction: Shorter, anatomically shaped and proximally loading stems have been developed to achieve better stress distribution and be more bone preserving. The purpose of this prospective study was to evaluate the migration pattern of the Proxima™ ultra-short uncemented stem using radiostereometric analysis (RSA), and to review the literature regarding the migration of short stemmed hip arthroplasty. Methods: 25 patients (28 hips) with hip osteoarthritis received a Proxima stem during total hip arthroplasty (THA). To measure stem migration, repeated RSA examinations were done during a 2 year follow up period. The patients were evaluated with the hip specific (HOOS) and the generic health (EQ5D) scores up to 1 year, and clinically for 6 years postoperatively. Results: Almost all migration occurred within the first 3 months, with mean subsidence of 0.22 mm and varus rotation of 1.04°, being the primary effect variables. After the third postoperative month and up to the 2 year RSA follow up no further significant migration occurred. The outcome scores showed substantial improvement after 1 year. No revisions were performed or indicated for any stem after a mean clinical follow up of 72.1 months. Conclusions: Like many other uncemented stems, the Proxima showed early migration up to 3 months hereafter osseointegration seems to have occurred. The achieved stability and clinical outcomes indicate favorable early results for this stem in younger patients who have good bone quality and average BMI. We found, however, the surgical technique to be slightly more demanding compared to conventional stems owing to the unique implant design that necessitates specific adjusted femoral cutting and broaching procedures.