Validation of three-dimensional model-based tibio-femoral tracking during running

Abstract

The purpose of this study was to determine the accuracy of a radiographic model-based tracking technique that measures the three-dimensional in vivo motion of the tibio-femoral joint during running. Tantalum beads were implanted into the femur and tibia of three subjects and computed tomography (CT) scans were acquired after bead implantation. The subjects ran 2.5m/s on a treadmill positioned within a biplane radiographic system while images were acquired at 250 frames per second. Three-dimensional implanted bead locations were determined and used as a "gold standard" to measure the accuracy of the model-based tracking. The model-based tracking technique optimized the correlation between the radiographs acquired via the biplane X-ray system and digitally reconstructed radiographs created from the volume-rendered CT model. Accuracy was defined in terms of measurement system bias, precision and root-mean-squared (rms) error. Results were reported in terms of individual bone tracking and in terms of clinically relevant tibio-femoral joint translations and rotations (joint kinematics). Accuracy for joint kinematics was as follows: model-based tracking measured static joint orientation with a precision of 0.2 degrees or better, and static joint position with a precision of 0.2mm or better. Model-based tracking precision for dynamic joint rotation was 0.9+/-0.3 degrees , 0.6+/-0.3 degrees , and 0.3+/-0.1 degrees for flexion-extension, external-internal rotation, and ab-adduction, respectively. Model-based tracking precision when measuring dynamic joint translation was 0.3+/-0.1mm, 0.4+/-0.2mm, and 0.7+/-0.2mm in the medial-lateral, proximal-distal, and anterior-posterior direction, respectively. The combination of high-speed biplane radiography and volumetric model-based tracking achieves excellent accuracy during in vivo, dynamic knee motion without the necessity for invasive bead implantation.

Can Joint Contact Dynamics Be Restored by Anterior Cruciate Ligament Reconstruction?

“…In vivo knee kinematics data were obtained during downhill running using a dynamic stereo x-ray (DSX) system and model-based tracking technique, as previously reported [2,3,13,21,32,33] and briefly described below. The patients performed moderate-speed running (2.5 m/ second) on an instrumented dual-belt treadmill (Bertec Corp, Columbus, OH, USA) with a 10°downward slope (Fig.…”

“…Three-dimensional (3-D) bone models were generated using medical imaging software (Mimics 1 ; Materialise Inc, Leuven, Belgium) to segment bone from soft tissue. Position and orientation of the tibia and femur were determined for each frame using a model-based tracking technique to align the radiographic image pairs to digitally reconstructed radiographs generated by projection through the 3-D bone model as described previously [2]. 2 The DSX system is shown.…”

“…We defined the anatomic coordinate systems from 3-D bone models as described previously [2,13,21,32,33]. Tibiofemoral translations were defined as the orthogonal components of a vector from the femoral anatomic origin (midpoint between the centers of the medial and lateral condyles) to the tibial anatomic origin (center of the tibial plateau), expressed in the tibial coordinate system.…”

“…We calculated knee kinematics using the conventions originally described by Grood and Suntay [16]. This kinematics measurement system has been used extensively for similar studies and is capable of tracking bone motion with precision in the order of 0.2 mm/0.2° [2]. During downhill running, tibial anterior translation and axial rotation were determined [21,32,33], and the magnitude of tibial anterior translation and axial rotation from foot strike to 0.1 second after foot strike were calculated for further analysis.…”

“…To measure joint contact sliding distance, the joint contact point on the surface of the femur and tibia was estimated using the distance-weighted centroid of the region of closest proximity at each time frame [2,21]. Tibial joint contact points (x n , y n , z n ) were described for the n th frame using a Cartesian coordinate system aligned with the tibial plateau.…”