A comparative study of peri-prosthetic bone mineral density measurement using two different dual-energy X-ray absorptiometry systems

24 patients aged 38-72 years with an uncemented total hip arthroplasty had dual-energy X-ray absorptiometry of the upper femur performed at a mean of 27 months after surgery. Each patient was scanned on both Lunar DPX and Hologic QDR-1000 densitometers. Peri-prosthetic bone mineral density (BMD) around the femoral component was measured in seven Gruen zones using software analysis techniques to allow quantification of bone mineral adjacent to a metal implant. There was a high correlation between the results obtained with the two systems (r = 0.94). BMD measurements using the Lunar DPX were 11% higher than with the Hologic QDR; however, there was a lack of agreement between the two instruments indicating that the two methods may not be used interchangeably.