Background The use of biplanar videoradiography technology has become increasingly popular for evaluating joint function in vivo. Two fundamentally different methods are currently employed to reconstruct 3-D bone motions captured using this technology. Marker-based tracking requires at least three radio-opaque markers to be implanted in the bone of interest. Markerless tracking makes use of algorithms designed to match 3-D bone shapes to biplanar videoradiography data. In order to reliably quantify in vivo bone motion, the systematic error of these tracking techniques should be evaluated. Method of approach Herein, we present new markerless tracking software that makes use of modern GPU technology, describe a versatile method for quantifying the systematic error of a biplanar videoradiography motion capture system using independent gold standard instrumentation, and evaluate the systematic error of the W.M. Keck XROMM Facility’s biplanar videoradiography system using both marker-based and markerless tracking algorithms under static and dynamic motion conditions. A polycarbonate flag embedded with 12 radio-opaque markers was used to evaluate the systematic error of the marker-based tracking algorithm. Three human cadaveric bones (distal femur, distal radius, and distal ulna) were used to evaluate the systematic error of the markerless tracking algorithm. The systematic error was evaluated by comparing motions to independent gold standard instrumentation. Static motions were compared to high accuracy linear and rotary stages while dynamic motions were compared to a high accuracy angular displacement transducer. Results Marker-based tracking was shown to effectively track motion to within 0.1 mm and 0.1° under static and dynamic conditions. Furthermore, the presented results indicate that markerless tracking can be used to effectively track rapid bone motions to within 0.15° for the distal aspects of the femur, radius, and ulna. Conclusions Both marker-based and markerless tracking techniques were in excellent agreement with the gold standard instrumentation for both static and dynamic testing protocols. Future research will employ these techniques to quantify in vivo joint motion for high-speed upper and lower extremity impacts such as jumping, landing, and hammering.

Background The thumb carpometacarpal (CMC) joint is often affected by osteoarthritis-a mechanically mediated disease. Pathomechanics of the CMC joint, however, are not thoroughly understood due to a paucity of in vivo data. Questions/purposes We documented normal, in vivo CMC joint kinematics during isometric functional tasks. We hypothesized there would be motion of the CMC joint during these tasks and that this motion would differ with sex and age group. We also sought to determine whether the rotations at the CMC joint were coupled and whether the trapezium moved with respect to the third metacarpal. Methods Forty-six asymptomatic subjects were CT-scanned in a neutral position and during three functional tasks (key pinch, jar grasp, jar twist), in an unloaded and a loaded position. Kinematics of the first metacarpal, third metacarpal, and the trapezium were then computed. Results Significant motion was identified in the CMC joint during all tasks. Sex did not have an effect on CMC joint kinematics. Motion patterns differed with age group, but these differences were not systematic across the tasks. Rotation at the CMC joint was generally coupled and posture of the trapezium relative to the third metacarpal changed significantly with thumb position. Conclusions The healthy CMC joint is relatively stable during key pinch, jar grasp, and jar twist tasks, despite sex and age group. Clinical Relevance Our findings indicate that directionally coupled motion patterns in the CMC joint, which lead to a specific loading profile, are similar in men and women. These patterns, in addition to other, nonkinematic influences, especially in the female population, may contribute to the pathomechanics of the osteoarthritic joint.

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