Abstract
BackgroundAseptic loosening due to bone remodelling processes after total hip replacement is one common cause for revision surgery. In human medicine, dual-energy X-ray absorptiometry (DEXA) is the gold standard for quantitative evaluation of bone mineral density, whereas in veterinary medicine conventional radiography is used for follow-up studies. Recently, a method has been described using digital X-ray images for quantitative assessment of grey scale values of bone contrast. Therefore, the aim of the present study was to evaluate the correlation of bone mineral density (BMD) measured by DEXA with grey scale values (GV) measured in digital X-ray images (RX50, RX66) ex vivo.ResultsThe measured GV in the chosen X-ray settings showed on average a good correlation (r = 0.61) to the measured BMD with DEXA. Correlation between the two X-ray settings was very good (r = 0.81). For comparisons among regions of interests (ROIs) a difference of 8.2% was found to be statistically significant, whereas in the case of RX50 and RX66 differences of 5.3% and 4.1% were found to be statistically significant.ConclusionsResults indicate that measuring absolute changes in bone mineral density might be possible using digital radiography. Not all significant differences between ROIs detectable with DEXA can be displayed in the X-ray images because of the lower sensitivity of the radiographs. However, direct comparison of grey scale values of the periprosthetic femur in one individual patient during the follow-up period, in order to predict bone remodelling processes, should be possible, but with a lesser sensitivity than with DEXA. It is important that the same X-ray settings are chosen for each patient for follow-up studies.
Highlights
Aseptic loosening due to bone remodelling processes after total hip replacement is one common cause for revision surgery
Measured bone mineral density (DEXA) and grey scale values (X-ray) for all Region of interest (ROI) in both ap1 and ap2 are displayed in Tables 1 and 2 (mean value (M) ± standard deviation (SD), coefficient of variation [CV])
A bisector line (Fig. 2; 2) was drawn in the middle between the tip of the prosthesis and a second line positioned at the proximal margin of Correlation between dual-energy X-ray absorptiometry (DEXA) and X-ray For ap1, correlation between DEXA and RX50 was good in ROI3 (r = 0.8) and in ROI1 (r = 0.6), moderate in ROI4 (r = 0.5) and ROI5 (r = 0.54) and poor in ROI2 (r = 0.34)
Summary
Aseptic loosening due to bone remodelling processes after total hip replacement is one common cause for revision surgery. Dual-energy X-ray absorptiometry (DEXA) is the gold standard for quantitative evaluation of bone mineral density, whereas in veterinary medicine conventional radiography is used for follow-up studies. The aim of the present study was to evaluate the correlation of bone mineral density (BMD) measured by DEXA with grey scale values (GV) measured in digital X-ray images (RX50, RX66) ex vivo. Different reasons for aseptic loosening processes are assumed, including particle disease, micromotion and stress shielding [12]. Stress shielding is due to different load transfer because of the higher modulus (E) of the prosthesis compared to bone which leads to loss of bone mineral density. It is necessary to detect as soon as possible the amount and localisation of bone loss around the prosthesis, which is reflected in changes in bone mineral density [13]
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