A determination of ankle kinematics using fluoroscopy

In vivo weight-bearing studies utilizing dynamic video fluoroscopy have bee n shown to offer an accurate and reproducible method for determining the ki nematics of a joint. The purpose of this study was to evaluate translationa l and rotational motions of the distal tibia relative to the talus in the s agittal and frontal planes. Ten subjects, each having a normal ankle and a total ankle arthroplasty on the opposite side (Buechel-Pappas Total Ankle, Endotec, South Orange, NJ), were studied under in vivo, weight-bearing cond itions using video fluoroscopy. All ten subjects were judged to have a succ essful arthroplasty without demonstrable pain or ligament instability. Unde r weight-bearing conditions, each subject performed successive motions movi ng from maximum dorsiflexion to plantarflexion, At maximum dorsiflexion, bo th the normal and implanted ankles had similar sagittal midline talar conta ct positions but with plantar flexion, implanted ankles had increased poste rior talar contact. Contact points on the distal tibia revealed that the la teral surface contacted at the midline or posterior throughout range-of-mot ion with minimal translation. The medial distal tibia contacted the talus p osterior on plantarflexion and often moved anteriorly with dorsiflexion. Th is translation described relative external rotation of the distal tibia on plantar flexion and internal rotation on dorsiflexion. The measured distanc es were larger for the implanted ankles with higher variability. The averag e range-of-motion was 37.4 degrees for normal ankles and 32.3 degrees for i mplanted ankles. This study defines the normal kinematic rotational and tra nslational motions of the ankle joint by accurately describing the three di mensional joint orientations. The implanted ankles experienced rotational a nd translational motions but had contacts more posterior, possibly related to surgical technique or alterations of ligamentous tension.