[Digital planimetry for exact assessment of peri-articular ossification].

PROBLEM

Currently, non-steroidal anti-inflammatory drugs (NSAID) and radiation have become established as methods of choice in the prevention of ectopic ossifications after total hip replacement. The most effective doses is still not known exact for both. Conventional classification systems only permit a rough distinction of ossifications, so they cannot be used for an exact quantitative measuring. Further, only a limited number of categories can be distinguished. We wanted to find out whether a quantitative measurement of ossifications can be realized, and if small differences in prophylactic effect can be detected in this way.

METHOD

By computerized digitized planimetry, 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 after operation. After marking the ossifications they were measured by drawing the outline with a magnifying glass-mouse. We checked all aspects of precision and reproducibility of the measurements and the comparability with an established classification method (Brooker).

RESULTS

The digitized planimetry could be performed on all patients X-rays. It gave a much more differentiated 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 conventional classification systems, it differentiates more subtly. In limited, well controlled studies slight differences of prophylactic methods on ossifications can be evaluated. New developments in X-ray technology will make the handling of this method even easier.