The data from this study suggest that future anterior cruciate ligament reconstruction techniques should reproduce not only anterior stability but also medial-lateral stability.

Accurately determining in vivo knee kinematics is still a challenge in biomedical engineering. This paper presents an imaging technique using two orthogonal images to measure 6 degree-of-freedom (DOF) knee kinematics during weight-bearing flexion. Using this technique, orthogonal images of the knee were captured using a 3-D fluoroscope at different flexion angles during weight-bearing flexion. The two orthogonal images uniquely characterized the knee position at the specific flexion angle. A virtual fluoroscope was then created in solid modeling software and was used to reproduce the relative positions of the orthogonal images and X-ray sources of the 3-D fluoroscope during the actual imaging procedure. Two virtual cameras in the software were used to represent the X-ray sources. The 3-D computer model of the knee was then introduced into the virtual fluoroscope and was projected onto the orthogonal images by the two virtual cameras. By matching the projections of the knee model to the orthogonal images of the knee obtained during weight-bearing flexion, the knee kinematics in 6 DOF were determined. Using regularly shaped objects with known positions and orientations, this technique was shown to have an accuracy of 0.1 mm and 0.1 deg in determining the positions and orientations of the objects, respectively.

BACKGROUND Previous studies have suggested injury to the anterior talofibular ligament may be linked to altered kinematics and the development of osteoarthritis of the ankle joint. However, the effects of ATFL injury on the in vivo kinematics of the ankle joint are unclear. HYPOTHESIS Based on the orientation of the ATFL fibers, we hypothesized that ATFL deficiency would lead to increased anterior translation and increased internal rotation of the talus relative to the tibia. STUDY DESIGN Controlled laboratory study. METHODS The ankles of 9 patients with unilateral ATFL injuries were compared as they stepped onto a level surface. Kinematic measurements were made as a function of increasing load. Using magnetic resonance imaging and orthogonal fluoroscopy, the in vivo kinematics of the tibiotalar joint were measured in the ATFL deficient and intact ankles from the same individuals. RESULTS A statistically significant increase in internal rotation, anterior translation, and superior translation of the talus was measured in ATFL deficient ankles as compared to intact, contralateral controls. For example, at 100% body weight, ATFL deficient ankles demonstrated a statistically significant increase in anterior translation of 0.9 ± 0.5mm (p = 0.008). At 100% body weight, the ATFL deficient ankle was internally rotated relative to the intact ankle by 5.7 ± 3.6° (p = 0.008). There was a slight increase of 0.2 ± 0.2mm in the superior translation of the ATFL deficient ankle compared to the intact ankle at 100% body weight (p = 0.02). CONCLUSIONS ATFL deficiency increases anterior translation, internal rotation, and superior translation of the talus. CLINICAL RELEVANCE Altered kinematics may contribute to the degenerative changes observed with chronic lateral ankle instability. These findings might help to explain the degenerative changes frequently observed on the medial talus in patients with chronic ATFL insufficiency and provide a baseline for improving ankle ligament reconstructions aimed at restoring normal joint motion.