[Validity and reproducibility of osteodensitometric DEXA-measurements following total hip endoprosthesis]

For the determination of reproducibility of bone densitometric measurements we performed a measurement according to the DEXA- method. 35 patients after implantation of total hip replacement were examined with a Lunar DPX-L. We received a maximum reproduction error of 1.2% according to the GRUEN-analysis. The operated hip of 17 patients showed an increase in bone density between 5 and 18% by the implantation of an arthroplasty compared to the preoperative values. The non-operated prosthesis-corrected hip showed a reproduction error of 3.8% in ROI 1 in 17 patients, otherwise a maximum of 1.3%. Considering an interfemoral difference in bone density of up to 20%, differences in periprosthetic bone density of up to 40% compared to the contralateral side can be within the normal range in a retrospective measurement. Therefore retrospective determination of bone density after cementless hip arthroplasty only is of limited value. Only prospective analysis can provide reliable information about the actual loss of bone density.