Abstract
Computer-assisted techniques are developed to optimise the positioning of acetabular cups in total hip replacement. However, ordinary guiding devices are still most commonly used. The aim of this study was to evaluate the accuracy when using a simple mechanical guiding device.
30 patients were operated by an experienced hip surgeon. A lateral position and a lateral approach were used. An un cemented press fit cup (Trilogy AB) was inserted using the guiding device for this type of pros-thesis, aiming 45 degrees abduction and 20 degrees ante-version. Radiological investigations were performed one week and three months postoperatively. Frontal views of the pelvis and of the operated hip were obtained. After scanning the contour of the opening of the acetabular prosthesis was identified and digitised using an edge detecting technique. The axes of the ellipsis of the acetabular opening served for calculation of the version of the cup. A lateral view clarified whether the cup was ante- or retroverted. The abduction related to the teardrop-line was measured on the scanned pelvic radiograph.
One week postoperatively mean abduction was 50 degrees (37–62), SD 5 degrees. Mean anteversion measured on the pelvic view was 9 degrees (2–23), SD 5 degrees, compared to 11 degrees (4–24), SD 5 degrees, on the frontal view of the hip joint 50 per cent of the cups showed a deviation of more than 10 degrees from the aimed anteversion.. At average the anteversion was 2 degrees lower when measured on the pelvic view compared to that measured on the AP-view of the hip. There were no significant differences between the measurements at one week and three months.
The anteversion of uncemented press fit acetabular components tends to be lower than intended when using a simple guiding device. The risk of an unacceptable abduction seems negligible. The inaccuracy in acetabular positioning may be due to inadequate positioning of the pelvis or inaccurate insertion technique.
Correspondence should be addressed to Richard Komistek, PhD, International Society for Technology in Arthroplasty, PO Box 6564, Auburn, CA 95604, USA. E-mail: ista@pacbell.net
