Abstract

The aim of this study was to analyze the bone remodeling around the Nanos® stem (Smith & Nephew, Marl, Germany) after primary total hip arthroplasty for coxarthrosis.
In 25 patients (15 male, 10 female, mean age 59.9 years) with the diagnosis of coxarthrosis, a DEXA scan was performed immediately after surgery, 97 days (SD 6.1 days) and 368 days (SD 6.2 days) after implantation of a Nanos® prosthesis. Plain radiographs were analyzed digitally for radiolucent lines, varus-valgus femoral stem alignment, measurement of stem migration and changes in varus-valgus femoral stem alignment. The position of the center of rotation (COR) and the offset were assessed pre- and postoperatively. Harris Hip Score was used to evaluate the clinical outcome.

The DEXA scan showed a significant and relevant increase in BMD (Bone Mineral Density) in Gruen-Zone 6 (12%) and a decrease in Zone 1 (15%), 2 (5%) and 7 (12%), which was interpreted as reflecting a distal load transfer in the metaphysis of the femur.

There was no clinically relevant migration or tilting of the Nanos® stem. Radiolucent lines were noted in 12 cases, mainly at the polished tip area of the prosthesis ; this was not regarded as a sign of impaired osseointegration. There was no significant difference between the position of the COR and the pre- and postoperative offset.

The absence of stem migration, angulation, or Relevant radiolucent lines is seen as evidence for an unimpaired osseointegration of the Nanos® stem approximately 12 months after implantation. It is concluded that the Nanos® prosthesis can reduce loss of BMD of the proximal femur composed with conventional stems or other short-stemmed implants.