Geometric analysis and clinical outcome of two cemented stems for primary total hip replacement with and without modular necks.

Abstract

Restoration of the physiological biomechanical principles of the hip is crucial in total hip replacement. The aim of this study was to compare an arthroplasty system with different offset options (a: Exeter®) with a dual-modular stem (b: Profemur Xm®). A local and an inertial coordinate system were used to assist the description of the components' assembly in the prosthesis. A resection line of the femoral head in standard position was added to the arthroplasties and geometric parameters were measured. The outcomes of 93 patients were clinically evaluated (a: n=50, b: n=43). Preoperative planning was compared to postoperative radiographs (femoral offset, leg-length), and clinical scores (HHS, WOMAC, total range of motion) were assessed preoperatively, and then 1 and 2years after surgery. The Exeter® offers an offset range from 32.1 to 56.9mm and the Profemur Xm® a range from 29.3 to 55.3mm. The leg-length variability of the Profemur Xm® has a range of 25.9mm, the Exeter® a range of 13.7mm. The Profemur Xm® offers more possible combinations of offset and leg-length reconstruction. The neck-stem angles of the Exeter® range from 125.2° to 126.3°, of the Profemur Xm® from 127.2° to 142.6°. There was no statistically significant difference in clinical outcome and radiological parameters. We conclude that both stems offer a wide range of options for anatomical reconstruction of the hip resulting in similarly good clinical results. The Profemur Xm® stem has advantages for the reconstruction of hips that deviate from standard anatomy but has the drawback of additional corrosive wear at the stem/neck interface.