THE USE OF COMPUTERIZED TOMOGRAPHY IN THE ASSESSMENT OF ANGULAR LIMB DEFORMITIES

Modern methods of deformity correction such as the Taylor Spatial Frame (TSF) allow correction of deformities to within tolerances of 1° and 0.5mm. Plain X-radiography using orthogonal views is the current standard for the assessment for the evaluation of angular limb deformities. CT has been used for the assessment of torsional and axial deformities but its use has not been described for the measurement of angular deformities. Furthermore, dedicated correction planning software (SpatialCad™) may allow more accurate deformity definition. This study aims to evaluate the accuracy of CT and SpatialCad™ to measure angular deformities in vitro. A tibia sawbone was coated in radio-opaque paint. A TSF was mounted on it and an osteotomy made in the mid-diaphyseal region. Four deformities were created and imaged with plain radiography and CT. Four observers measured the deformities using paper and pencil, PACS and SpatialCad™ for plain radiographs and Spatial-Cad™ for the CT scout views. The variance of the mean response of observed differences between main treatment factors was measured using analysis of variance. There was no significant difference in variability (precision) between observers or methods of measurement. However, measurements made with PACS and Spatial-Cad™ on plain radiographs, but not CT scout views, were also accurate. There does not appear to be any evidence at present that the use of CT for measurement of angular limb deformity is justified over plain radiography. Spatial-Cad™ is designed to optimize deformity correction planning for use with TSF, but PACS appears to be adequate for use with other deformity correction systems.