Validation of dynamic biplane radiography and three-dimensional model-based tracking for evaluation of dynamic thumb kinematics.

Dynamic biplane radiography (DBR) in conjunction with model-based tracking (MBT) has provided a suitable mechanism for biomechanical assessment of many joints but has not yet achieved widespread use at the thumb and wrist. The purpose of this work is to determine the accuracy of DBR with markerless MBT for the evaluation of thumb and wrist joint kinematics. Three 0.6 mm stainless steel beads were implanted into each trapezium, scaphoid, first metacarpal, and radius of three cadaveric upper extremities. Each specimen was manipulated in thumb abduction/adduction, thumb flexion/extension, wrist radioulnar deviation, and wrist flexion/extension while synchronized biplane radiographs were collected at 100 Hz. Specimen-specific 3D bone models were created from CT scans. MBT was performed by optimizing the correlation between digitally reconstructed radiographs, created from the volumetric CT-based bone models, and the biplane radiographs. Joint kinematics and joint space were calculated and compared between the "gold standard" bead-based tracking and markerless MBT. The MBT system accuracy (RMS error) in measuring bone position for the static and dynamic trials was 0.25 mm and 0.58 mm, respectively. The overall MBT system accuracy in measuring dynamic joint kinematics was 1.3 mm in translation and 5.0° in rotation. The MBT system accuracy in measuring dynamic joint space was 0.4 mm. DBR with MBT is a non-invasive and accurate method that can be utilized for kinematic analysis of the thumb and wrist.