A method for measuring joint kinematics designed for accurate registrationof kinematic data to models constructed from CT data

A method for measuring three-dimensional kinematics that incorporates the d irect cross-registration of experimental kinematics with anatomic geometry from Computed Tomography (CT) data has been developed. Plexiglas registrati on blocks were attached to the bones of interest and the specimen was CT sc anned. Computer models of the bone surface were developed from the CT image data. Determination of discrete kinematics was accomplished by digitizing three pre-selected contiguous surfaces of each registration block using a t hree-dimensional point digitization system. Cross-registration of bone surf ace models from the CT data was accomplished by identifying the registratio n block surfaces within the CT images. Kinematics measured during a biomech anical experiment were applied to the computer models of the bone surface. The overall accuracy of the method was shown to be at or below the accuracy of the digitization system used. For this experimental application, the ac curacy was better than +/-0.l mm for position and 0.1 degrees for orientati on for linkage digitization and better than +/- 0.2 mm and +/- 0.2 degrees for CT digitization. Surface models of the radius and ulna were constructed from CT data, as an example application. Kinematics of the bones were meas ured for simulated forearm rotation. Screw-displacement axis analysis showe d 0.1 mm (proximal) translation of the radius (with respect to the ulna) fr om supination to neutral (85.2 degrees rotation) and 1.4 mm (proximal) tran slation from neutral to pronation (65.3 degrees rotation). The motion of th e radius with respect to the ulna was displayed using the surface models. T his methodology is a useful tool for the measurement and application of rig id-body kinematics to computer models. (C) 2001 Elsevier Science Ltd. All r ights reserved.