Digitized planimetry for measurement of ectopic bone formation.

Problem: Currently, non-steroidal anti-inflammatory drugs (NSAID) and radia tion have become established as methods of choice in the prevention of ecto pic ossifications after total hip replacement. The most effective dosis is still not known exact for both. Conventional classification systems only pe rmit a rough distinction of ossifications, so they cannot be used for an ex act quantitative measuring. Further, only a limited number of categories ca n be distinguished. We wanted to find out whether a quantitative measuremen t of ossifications can be realized, and if small differences in prophylacti c effect can be detected in this way. Method: By computerized digitized pla nimetry, we measured ossifications of patients after total hip replacement on plain X-rays of the pelvis. We followed 57 patients for up to 2 years af ter operation. After marking the ossifications they were measured by drawin g the outline with a magnifying glass-mouse. We checked all aspects of prec ision and reproducibility of the measurements and the comparability with an established classification method (Brooker). Results: The digitized planim etry could be performed on all patients Xrays. It gave a much more differen tiated picture compared to the method of Brooker. The method is simple and reproducible, but time consuming. Conclusions: Digitized planimetry allows a very exact measurement of ectopic bone formation. Compared to conventiona l classification systems, it differentiates more subtly. In limited, well c ontrolled studies slight differences of prophylactic methods on ossificatio ns can be evaluated. New developments in X-ray technology will make the han dling of this method even easier.