MEASUREMENTS OF THE TOTAL ELBOW PROSTHESIS – IS THE COMPUTER A RELIABLE TOOL?

Abstract

Introduction: Electronic storage of X-rays is becoming standard. It would therefore, be highly desirable to use a computer as a tool for obtaining useful measurements from radiographs. The current study investigates the reliability of computerised measurements of radiographs of the Souter-Strathclyde elbow.

Materials and Methods: 56 AP radiographs of Souter-Strathclyde Elbows were assessed for the parameters described by Trail et al (1999). The respective x-rays were digitised using a transparency flatbed scanner with a resolution of 80 _m/pixel. The radiographs were then measured for the migration and movement of the prosthesis using the following lines: Hapd1, Hapd2, Hapd3 Hapd4. All the radiographs were measured twice manually with at least one week interval, the observer being blind to the initial results at the time of the second measurement. The x-rays were again measured twice using the computer and a measuring software developed in our own department. The results were analysed for intra observer variability, using paired t-test and Pearson correlations.

Results: Table 1 shows the results of the paired measurements, with the confidence intervals for the mean error, the p for the paired t-test and the correlations between the paired readings. M1 and M2 represent the manual readings, while C1 and C2 the computerised readings.

Conclusions: The mean error of all paired readings was below 1 mm. The correlation between all paired readings was highly significant, with all the paired readings with the computer as a tool being .99. The only difference that was statistically significant was Hapd3M1-M2, between two manual measurements, although the mean error is not clinically relevant, still being less than 1mm. We conclude that computerised measurements of radiographs are at least as reliable as those conducted directly on film.