23. IMAGE-BASED NAVIGATION IMPROVES THE POSITIONING OF THE HUMERAL COMPONENT IN TOTAL ELBOW ARTHROPLASTY

Abstract

Purpose: This study evaluated the accuracy of humeral component alignment in total elbow arthroplasty. An image-based navigated approach was compared against a conventional non-navigated technique. We hypothesized that an image-based navigation system would improve humeral component positioning, with navigational errors less than or approaching 2.0mm and 2.0°.

Method: Eleven cadaveric distal humeri were imaged using a CT scanner, from which 3D surface models were reconstructed. Non-navigated humeral component implantation was based on a visual estimation of the flexion-extension (FE) axis on the medial and lateral aspects of the distal humerus, followed by standard instrumentation and positioning of a commercial prosthesis by an experienced surgeon. Positioning was based on the estimated FE axis and surgeon judgment. The stem length was reduced by 75% to evaluate the navigation system independent of implant design constraints. For navigated alignment, the implant was aligned with the FE axis of the CT surface model, which was registered to landmarks of the physical humerus using the iterative closest point algorithm. Navigated implant positioning was based on aligning a 3D computer model calibrated to the implant with a 3D model registered to the distal humerus. Each alignment technique was repeated for a bone loss scenario where distal landmarks were not available for FE axis identification.

Results: Implant alignment error was significantly lower using navigation (P< 0.001). Navigated implant alignment error was 1.2±0.3 mm in translation and 1.3±0.3° in rotation for the intact scenario, and 1.1±0.5 mm and 2.0±1.3° for the bone loss scenario. Non-navigated alignment error was 3.1±1.3 mm and 5.0±3.8° for the intact scenario, and 3.0±1.6 mm and 12.2±3.3° for the bone loss scenario. Without navigation, 5 implants were aligned outside 5° for intact bone while 9 were aligned outside 10° for the bone loss scenario.

Conclusion: Image-based navigation improved the accuracy of humeral component placement to less than 2.0 mm and 2.0°. Further, outliers in implant positioning were reduced using image-based navigation, particularly in the presence of bone loss. Implant malalignment may well increase the likelihood of early implant wear, instability and loosening. It is likely that improved implant positioning will lead to fewer implant related complications and greater prosthesis longevity.