Abstract
Purpose: Current techniques for the investigation of elbow stability following injury or surgical interventions rely on kinematic descriptors. Typically, the motion pathways of the bones are employed to describe the effect of various clinical variables on alignment joint stability. This study describes a new approach to better visualize joint motion pathways that relates the anatomical geometry of the joint, obtained using medical imaging, with the recorded motion of the joint. The clinical aim of our study was to use this approach to investigate the effect of radial head resection and subsequent radial head arthroplasty on joint kinematics and elbow stability.
Method: Five fresh-frozen cadaveric specimens were employed. Computed tomography (CT) scans of each upper extremity were obtained to create a three-dimensional model of the joint. Simulated active elbow flexion with the arm in the valgus gravity loaded position was achieved using an upper arm simulator previously developed in our laboratory. Receivers from an electromagnetic tracking device were attached to the humerus and ulna in order to record their relative motion. Sutures were secured to the tendons of relevant muscles, which were connected to servomotors and pneumatic actuators, used to simulate motion. Kinematic data was collected with the radial head intact, radial head resected and following placement of metallic radial head implant. A repeated-measures analysis of variance was used to detect statistical differences. After testing, each specimen was denuded of all soft tissue and disarticulated. Fiducial markers were attached to the humerus and the ulna. The joint was then re-imaged in the CT scanner to obtain a volumetric image of each fiducial. Using the kinematic data recorded during simulated motion, and the knowledge of the position of each fiducial, a direct visualization of the recorded motion, using the 3D models was obtained. The bony position was then compared to the traditional graphical kinematic analysis examining changes in valgus angulations throughout the arc of motion.
Results: We observed a close agreement between the kinematic output and the registered bony 3D models showing the joint position. Following resection of the radial head, in the valgus dependent position, there was an increase in the valgus angulation of the ulna with respect to the humerus (p< 0.05).
Conclusion: Using this visualization approach, these changes in bony alignment were readily observed and understood visually in the 3D model of the ulna. Unlike the traditional graphical approach used to investigate elbow stability, this technique allows for the representation of coupled motion (rotation) of the bones. This technique also permits direct visualization the relative position of the bones within the joint, hence improving the overall understanding of joint motion.
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