New cementless fixation in hip arthroplasty: a radiostereometric analysis

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 study was to evaluate the stability of the Scyon total hip replacement (THR) stem in-vivo.

A total of 15 patients, with an average age of 50 years had surgery between 2008 and 2011. Each patient received a Scyon THR. Standard questionnaires were completed at each follow-up visit for evaluation of functional outcomes. RSA, patient reported outcomes, and plain radiographic follow-up were obtained at 6 months, 1 year, 2 years, and 5 years postoperatively.

The median ± standard error (SE) stem subsidence (negative y-translation) was 0.07 ± 0.07 mm at 1 year, 0.05 ± 0.04 mm at 2 years and 0.04 ± 0.13 mm 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 radiographs showed bone on-growth onto 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 5 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.