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°r otation and in 20 patients at 30° rotation. Rotation within 30° 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. J Bone Joint Surg [Br] 2000;82-B:1065-71. Received 8 January 1999; Accepted after revision 27 August 1999Measurements of the bone mineral density (BMD) of the proximal femur after arthroplasty of the hip have been made for a number of years, mainly in retrospective studies [1][2][3][4][5] in which a reduction of up to 50% has been observed compared with the non-operated side. Prospective studies could not predict a reduction in BMD by this amount. The maximum reduction of BMD two years after arthroplasty was 38% compared with the immediate postoperative density of the operated femur. 6-10 Direct comparison of retroand prospective studies is not possible since the implant time of the prostheses is markedly different and it has not been possible to identify the degree to which the BMD of both femora differ because of individual differences, and the effect of implantation of an uncemented stem. 11We have compared the preoperative with the immediate postoperative BMD and examined the effect of implantation. The method of measurement and the influence of rotation in vitro and in vivo after implantation of an uncemented custom-made femoral stem were compared with those in standard uncemente...

Long-term study of bone remodelling after femoral stem: A comparison between dexa and finite element simulation

“…It is accepted that most of the remodelling is established at the end of the first postoperative year, reaching a balance in BMD from this moment onwards (Sychter and Engh, 1996;Martini et al, 2000;Gibbons et al, 2001). The obtained results suggest that this stability appears between the 6th and 12th month, when the changes in BMD reflect the biochemical response of the bone, in accordance to Wolff's law.…”

“…These changes explain that with first generation cemented stems the losses in density reached up to 45% (Sychter and Engh, 1996;McAuley et al, 2000;Sychter et al, 2002), with second generation stems still reaching between 20% and 25% at the end of the first or second year (Ka¨rrholm et al, 2002) and with tapered stems decreases between 10% and 30% were found with proximal predominance (Gibbons et al, 2001;Schmidt et al, 2004). Custom made implants had decreases in proximal areas of 10-15% at the end of the first year (Zerahn et al, 1998;Martini et al, 2000); femoral stems with reduced stiffness showed 15% reduction in the calcar at the end of the second year (Ka¨rrholm et al, 2002;Nagi et al, 2006).…”

Computed Tomography Assisted Osteodensitometry in Total Hip Arthroplasty

“…1,2,4,5,6,20 Other studies have reported a BMD loss of greater than 50% in the calcar region. 5 Studies on cementless stems have shown a recovery of bone density after an initial postoperative bone loss.…”

“…11 HA-coated implants have a good clinical and radiological outcome with more favourable bone remodelling and implant fixation when compared with porous-coated implants. 4,5,12,13,14 Histological analyses in cadaveric specimens have shown sound proximal and distal HA stem-bone osteointegrations in a relatively short period. 15,16 Such findings could reduce proximal stress shielding and provide a circumferential barrier to wear debris that induces osteolysis.…”

“…1 Bone remodelling could be a result of ageing, stress redistribution, prosthetic design, implant stiffness and load-transfer mechanisms. [1][2][3][4][5] Mechanical load forces continuously expose the bone to a remodelling process according to the Wolff's law, where an increased load leads to a gain in bone mass and decreased load results in a loss. 6 Bone-density loss and remodelling of the proximal femur have been considered as potential factors determining subsidence or periprosthetic fractures.…”