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Saturday, March 3, 2001

Computer-based technology increases implant accuracy

Computer-based surgical navigation technologies can reliably measure acetabular implant alignment in real time during surgery and are more accurate than mechanical guides, according to investigators in poster exhibit 39.

They point out that careful alignment of the components is critical to ensure satisfactory outcomes in total hip replacement (THR). Several factors (e.g., patient positioning and instrumentation) influence component placement, but until recently it has been difficult to measure the individual contributions to the overall result.

With the advent of computer based surgical navigation systems, these factors can now be measured intraoperatively. In this study a navigation system was used to measure acetabular component alignment both during and after pressfitting cups and after any supplementary screw fixation.

For a series of 128 patients undergoing THR, optical targets were attached to the pelvis and the cup placement tool. An image guided tracking system (with inaccuracies of less than one millimeter and one degree) was used to continuously measure the tool angle with reference to the pelvis, providing real time cup abduction and flexion angles.

These angles were recorded as the acetabular component was placed during and after pressfitting, and after the placement of supplementary screws when used. Surgical navigation during THR improved the accuracy and reliability of acetabular alignment. The final cup alignment using computer assisted navigation was within 3 degrees (SD 4) of abduction and 5 degrees (SD 5) of flexion when compared to the desired pre-op alignment. The process of pressfitting the cup and supplementary screw fixation was noted to influence the final cup orientation and these changes were not always easily detected visually.

The investigators are Anthony M. DiGioia III, MD; James E. Moody Jr., MS; Branislav Jaramaz, PhD; Richard S. LaBarca, MS; and Constantinos Nikou, MS, all of Pittsburgh, Pa.

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Last modified 20/February/2001 by IS