Precision of the measurements of periprosthetic bone mineral density in hips with a custom-made femoral stem

Abstract

Our aim was to determine the precision of the measurements of bone mineral density (BMD) by dual-energy x-ray absorptiometry in the proximal femur before and after implantation of an uncemented implant, with particular regard to the significance of retro- and prospective studies. We examined 60 patients to determine the difference in preoperative BMD between osteoarthritic and healthy hips. The results showed a preoperative BMD of the affected hip which was lower by a mean of 4% and by a maximum of 9% compared with the opposite side. In addition, measurements were made in the operated hip before and at ten days after operation to determine the effect of the implantation of an uncemented custom-made femoral stem. The mean increase in the BMD was 8% and the maximum was 24%. Previous retrospective studies have reported a marked loss of BMD on the operated side. The precision of double measurements using a special foot jig showed a modified coefficient of variation of 0.6% for the non-operated side in 15 patients and of 0.6% for the operated femur in 20 patients. The effect of rotation on the precision of the measurements after implantation of an uncemented femoral stem was determined in ten explanted femora and for the operated side in ten patients at 10 degrees rotation and in 20 patients at 30 degrees rotation. Rotation within 30 degrees influenced the precision in studies in vivo and in vitro by a mean of 3% and in single cases in up to 60%. Precise prediction of the degree of loss of BMD is thus only possible in prospective cross-sectional measurements, since the effect of the difference in preoperative BMD, as well as the apparent increase in BMD after implantation of an uncemented stem, is not known from retrospective studies. The DEXA method is a reliable procedure for determining periprosthetic BMD when positioning and rotation are strictly controlled.

Continuous bone loss around a tapered uncemented femoral stem: A long-term evaluation with DEXA

“…Caution must be exercised when interpreting and comparing results from different studies, since several influences must be considered such as: surgical approach (Perka et al 2005), definition of ROIs, leg position (Cohen and Rushton 1995a), pre-or postoperative baseline value (Kröger et al 1996), and cross-sectional or longitudinal studies (Martini et al 2000). However, a tendency towards a better retained proximal BMD has been found after implantation of thinner tapered stems without porous coating.…”

The cementless Bicontact® stem in a prospective dual-energy X-ray absorptiometry study

“…1 The cementless Bicontact® stem is tapered, with a rough proximal hydroxyapatite coating and a smooth distal portion 20°internal rotation. The foot was secured in the Hologic foot positioning device in order to obtain reproducible rotation in all patients to limit measurement errors, as it has been demonstrated that rotation influences BMD measurement [9][10][11]. DEXA precision was assessed on all patients, and all underwent sequential DEXA examinations of the contralateral unoperated hip and the proximal femur-taken preoperatively and one week later.…”

The Adaptiva custom-made stem—our reasons for not using it anymore

“…The principle of the device is a fit and fill pressfit into the proximal femur especially on the medial and lateral side. Martini et al were able to show in measurements of bone mineral density (BMD) that 10 days after operation there was a mean increase in the BMD of the replaced hip of 8% with a maximum of 24% [17]. Götze et al showed in cadaveric femurs a high primary stability in custom-made Adaptiva femoral stems with respect to subsidence, rotation, and interface motion [9].…”