Abstract
To determine the precision of conventional versus computer assisted techniques for positioning the acetabular component in total hip arthroplasty (THA).
Malposition of the acetabular component during THA increases the occurrence of impingement, reduces range of motion, and increases the risk of dislocation and long-term wear. To prevent malpositioned hip implants, an increasing number of computer assisted surgery systems have been described, but their accuracy is not well established.
Using a lateral approach, 150 cups were placed by 10 different surgeons in 10 identical plastic pelvis models. Only the immediate operating field was visible. Pre-operative planning was performed with a computerised tomography scan. Fifty cups were placed free hand, 50 others with the standard cup positioner, and the remaining 50 cups using computer-assisted orthopaedic surgery (Medivision). The accuracy of cup abduction and anteversion was assessed with an electromagnetic system (Fastrak™).
Using conventional techniques, free hand placement revealed a mean precision of cup anteversion and abduction of 10° (range 5.5 to 14) and 3.5° (2.5 to 5) respectively. With the cup positioner, these angles measured 8° (5 to 10.5) and 4° (3 to 5.5) respectively, and using the computer assisted method, the mean cup anteversion precision was 1.5° (1 to 2) and mean cup abduction measured 2.5° (2 to 3.5).
Computer assisted cup placement is a very accurate and reproducible technique during THA. It is clearly more precise than either of the two traditional methods of cup positioning, even for well-trained surgeons.
The abstracts were prepared by Nico Verdoschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, Universitair Medisch Centrum, Orthopaedie / CSS1, Huispost 800, Postbus 9101, 6500 HB Nijmegen, Th. Craanenlaan 7, 6525 GH Nijmegen, The Netherlands.
