A moving fluoroscope to capture tibiofemoral kinematics during complete cycles of free level and downhill walking as well as stair descent

Abstract

Videofluoroscopy has been shown to provide essential information in the evaluation of the functionality of total knee arthroplasties. However, due to the limitation in the field of view, most systems can only assess knee kinematics during highly restricted movements. To avoid the limitations of a static image intensifier, a moving fluoroscope has been presented as a standalone system that allows tracking of the knee during multiple complete cycles of level- and downhill-walking, as well as stair descent, in combination with the synchronous assessment of ground reaction forces and whole body skin marker measurements. Here, we assess the ability of the system to keep the knee in the field of view of the image intensifier. By measuring ten total knee arthroplasty subjects, we demonstrate that it is possible to maintain the knee to within 1.8 ± 1.4 cm vertically and 4.0 ± 2.6 cm horizontally of the centre of the intensifier throughout full cycles of activities of daily living. Since control of the system is based on real-time feedback of a wire sensor, the system is not dependent on repeatable gait patterns, but is rather able to capture pathological motion patterns with low inter-trial repeatability.

Fig 1. Moving fluoroscope developed at the Institute for Biomechanics.

Consisting of a C-arm mounted on a moving trolley, allows real time tracking of the knee throughout complete cycles of level walking, stair descent and ramp descent activities. The figure shows the set up for measurements of the left knee. For measurements of the right knee, the C-arm is rotated by 180° around its out of plane axis and the front bar, including wire sensor is reconfigured to the other side of the trolley, such that the C-arm always leads away from the subject due to safety considerations.

Fig 2. Wire sensor.

Tracking of the trolley is achieved by positional feedback of the subject’s knee using a wire sensor and digital goniometer, thus allowing tracking of the knee joint both horizontally and vertically.

Fig 3. Instrumented staircase and ramp.

Staircase and ramp (10° inclination) including two mobile force plates.

Fig 4. Tracking of the knee joint.

Movement of the knee joint centre relative to the image intensifier during level walking, stair descent and downhill walking. All trials for all 10 subjects are shown (one colour for each subject).