Measurement of Early Bone Loss Around a Total Hip Arthroplasty. A Prospective Trial With Dual Energy X-ray Absorptiometry.

Dual x-ray absorptiometry (DXA) has become the most used and proven to be a precise method to investigate changes in bone mass density (BMD). Research with DXA has shown the pattern of bone remodelling around an implant. Results from implant studies are often presented as changes in BMD as a function of time. The baseline and reference value for such calculations is the first measurement after the operation. The most pronounced bone loss after implantation of hip prosthesis usually comes within 3 months. The baseline measurement is performed at different time from study to study. If there is a rapid bone loss the first weeks after an operation, this will influence the reference value and then the results. To evaluate DXA as a method we decided to set up a study with 3 DXA measurements within the first 2 weeks.

We included 23 patients operated with total hip prosthesis (THP). They were measured with DXA at 1, 5 and 14 days, 3 and 12 months after the operation. Results were given in percent (+/-SD) for each Gruen zone. There were no changes in bone density between the first 3 measurements. In all zones, except zone 1, the lowest BMD was measured after 3 months. We concluded that DXA measurements done within 14 days after the operation can be used as reference measurements for later follow ups.