TOOL BRACING FOR PERFORMANCE IMPROVEMENT IN SIMULATED FEMORAL HEAD-NECK OSTEOCHONDROPLASTY

Introduction Bracing, a strategy employed by humans and robotic devices, can be generally described as a parallel mechanical link between the actor, the environment, and/or the workpiece that alters the mechanical impedance between the tool and workpiece in order to improve task performance. In this study we investigated the potential value of bracing in the context of bone milling to treat cam-type femoroacetabular impingement (FAI) lesions. The goal of this study was to evaluate whether a proposed bracing technique could enable a user to perform a cam resection more accurately and quickly than a currently employed arthroscopic technique. Materials/Methods Test samples consisted of white urethane plastic reproductions of a commercially available adult proximal femur, which were laser scanned to obtain ground-truth surface information. A black cam lesion was then cast onto the surface of the femur in the anterosuperior region of the femoral neck, creating a clear visual resection boundary for the simulated osteochondroplasty. Test subjects were 4 adult males (25 +/− 3 years) with no surgical experience. Test conditions included two binary factors: (1) Braced vs. Unbraced – The braced case introduced a spherical bearing tool support mounted in the approximate anterolateral arthroscopic portal position. (2) Speed vs. Accuracy – The subject was instructed to perform the resection as quickly as possible or as accurately as possible with a moderate regard for time. Following the removal of the lesion, femurs were laser scanned to acquire the post-resection surface geometry, with accuracy being reported as RMS deviation between the pre- and post-resection scans over the anterosuperior neck region. Results In both accuracy and speed cases, bracing tended to reduce errors (on the order of 7–14%) and task duration (on the order of 32–52%), although given the small number of subjects in this pilot study, these differences were not statistically significant. Conclusion These results provide some encouragement that our hypothesis that bracing can improve both speed and accuracy of cam lesion resection by untrained subjects may be true. The standard deviations between subjects are high and are likely due to both the difficulty of the task and differences in experience using handheld power tools, so additional subjects would be needed to verify the trends identified here.