A TECHNIQUE FOR MEASURING THE SURFACE-AREA OF ARTICULAR-CARTILAGE IN ACETABULAR FRACTURES

The aim of this study was to develop a reliable technique for measurin g the area of a curved surface from an axial computed tomography (CT) scan and to apply this clinically in the measurement of articular cart ilage surface area in acetabular fractures. The method used was a tria ngulation algorithm. In order to determine the accuracy of the techniq ue, areas of hemispheres of known size were measured to give the perce ntage error in area measurement. Seven such hemispheres were machined into a Perspex block and their area measured geometrically, and also f rom CT scans by means of the triangulation algorithm. Scans of 1, 2 an d 4 mm slice thickness and separation were used. The error varied with slice thickness and hemisphere diameter. It was shown that the 2 mm s lice thickness provides the most accurate area measurement, while 1 mm cuts overestimate and 4 mm cuts underestimate the area. For a hemisph ere diameter of 5 em, which is of similar size to the acetabulum, the error was -11.2% for 4 mm cuts, +4.2% for 2 mm cuts and +5.1% for 1 mm cuts. As expected, area measurement was more accurate for larger hemi spheres. This method can be applied clinically to quantify acetabular fractures by measuring the percentage area of intact articular cartila ge. In the case of both column fractures, the percentage area of secon dary congruence can be determined. This technique of quantifying aceta bular fractures has a potential clinical application as a prognostic f actor and an indication for surgery in the long term.