gms | German Medical Science

Objectives: Scyon Orthopaedics AG developed a new mode of cementless fixation of the femoral component that provides immediate and permanent anchorage by monocortical locking screws. The aim of this prospective randomized study was to evaluate the stability of the Scyon THR stem in-vivo.

Methods: Fifteen patients, with an average age of 50 years had surgery between 2008 and 2011. Each patient received a Scyon total hip arthroplasty. Standard questionnaires were completed at each follow-up visit for evaluation of functional outcomes. Radiostereometric analysis (RSA), patient reported outcomes, and plain radiographic follow-up were obtained at 6 months, 1 year, 2 years, and 5 years postoperatively. To determine if there was significant migration of the implant, a Wilcoxon paired signed ranks test was used. This test was also used to determine differences in patient reported outcomes over time. A power analysis was performed for a 1 sample, two-tailed t-test with 80% power and the chance of a Type I error of 5%.

Results and Conclusion: The median±standard error (SE) stem subsidence (y-translation) was 0.07±0.07mm at 1 year, and 0.05±0.04mm at 2 years, and 0.04±0.13mm at 5 years. The median±SE stem rotation (y-rotation) was 0.1±0.21 degrees at 1 year, 0.51±0.31 degrees at 2 years and 0.60±0.37 degrees at 5 years. Plain radioraphs showed bone on-growth of medial aspect of the stem. Median HHS improved from 55 preoperatively to 93 at 1 year and 97 at 5 years. The median UCLA Activity Score improved from 4 preoperatively to 6 at 1 year and 5 years. RSA results indicate that the Scyon stem with its five monocortical locking screws is stable at 5 years. Immediate surgical fixation of the stem and bony on-growth onto the femoral component may ultimately decrease the rate of aseptic stem loosening in these THR patients.