Biplanar videoradiography is a validated method for measuring skeletal kinematics. However, using two X-ray source-detector pairs introduces geometric constraints that can compromise image quality. The spatial configuration of the two pairs often requires a larger object-to-image distance (OID). This setup leads to greater image magnification and reduced signal intensity at the detector, increasing the risk of underexposure. Consequently, visualization of deeper anatomical structures, such as the lumbar spine, can become challenging, and the effective field of view may be limited, restricting multi-joint analyses. To address this limitation, this proof-of-concept study evaluated a monoplane stereoscopic videoradiography (MSV) configuration. MSV uses two X-ray sources captured by a single detector, enabling a smaller OID. A pseudo-dynamic experiment was conducted to assess whether MSV would achieve accurate calibration and subsequent 3D bone positions. A cube and pelvis phantom were rotated 360° on a turntable in 15° increments. At each increment, positions were recorded using both conventional motion capture (MOCAP) and MSV, with MOCAP acting as the reference standard. During MSV image acquisition, a lead barrier alternately blocked one X-ray source, allowing the other to project onto the detector. Calibration was performed using a bundle adjustment technique, and 3D bone positions were calculated using radiostereometric analysis and model-based tracking and compared against MOCAP. Overall, MSV achieved sub-millimeter and sub-degree accuracy. The calibration yielded a mean residual of 0.22 mm, while rotational and translational biases ranged from 0.36-1.16° and 0.22-1.23 mm, respectively, with precisions of 0.09-0.59° and 0.18-0.58 mm. These results support the feasibility of using MSV to accurately calculate skeletal positions. This approach reduces magnification and inherently increases detector exposure, opening avenues for multi-joint analyses and improved imaging of deeper joints. Future work will focus on implementing a true asynchronous MSV acquisition to extend this approach to dynamic, in vivo kinematic studies.
Bugajski et al. (Wed,) studied this question.