Abstract
The purpose of this study was to compare the accuracy and precision of acetabular component placement in cadavers using conventional techniques and CT-based individualised guides by both orthopaedic trainees and surgeons.
Seven cadaveric pelvises underwent a computerised tomography (CT) scan and a three-dimensional virtual model was created. Based on this model, cup orientation was planned for 40 degrees of inclination and 20 degrees of anteversion and an individualised guide was designed. A physical model of the individualised guide was created using a Rapid Prototyping machine (dimension SST, Stratasys, Inc., USA).
The pelvises were mounted in the lateral position and covered with a soft tissue envelope exposing only the acetabulum as would be visualised during a lateral approach to the hip. A total of 26 participants (16 orthopaedic surgery residents, 10 orthopaedic surgeons) were asked to use an acetabular cup impactor to place the cup in 40 degrees of inclination and 20 degrees of anteversion. This was first completed for all seven pelvises using conventional placement. Each participant was then instructed on how to use the individualised guide. They were provided with the guide and an individualised acetabular model to practice placement. Once they were comfortable with the system they were then asked to use the individualised guides in each of the seven pelvises.
An optoelectronic navigation system was used to evaluate the accuracy of the placement of the acetabular cup. An Optotrak Certus Motion Tracking System (Northern Digital Inc., Waterloo, Canada) was used. An optoelectronic marker was attached to the acetabulum and a combined pair-point and surface matching was performed. After the guide was placed in the acetabulum, a tracked axial pointing device was aligned inside the guidance cylinder and its three-dimensional orientation stored. The angle deviation between the achieved position and the planned cup orientation was calculated.
There were no statistically significant differences between trainees and surgeons in either conventional placement or use of the individualised guides. There were no statistically significant differences in anteversion between the groups. The individualised guide showed statistical improvement in the absolute deviation from planned inclination compared to conventional placement (4.2° vs. 9.1°, p< 0.001) as well as a reduction in standard deviation (3.3 vs. 5.9, p< 0.001).
The use of individualised guides can improve the accuracy and precision in the placement of acetabular component positioning. The current guide design controls well for inclination, which is a key factor in the function of a total hip arthroplasty. Based on this data, we will implement design changes to better address version of the component. Future work will likely include comparison to computer-assisted cup placement as well.
