In vivo kinematics of the tibiotalar joint after lateral ankle instability

Abstract

Background: Previous studies have suggested that injury to the anterior talofibular ligament (ATFL) 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, ATFL deficiency leads to increased anterior translation and increased internal rotation of the talus relative to the tibia.

Study design: Descriptive 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. With use of magnetic resonance imaging and orthogonal fluoroscopy, the in vivo kinematics of the tibiotalar joint were measured in the ATFL-deficient and intact ankles of 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 with the intact contralateral controls. For example, at 100% body weight, ATFL-deficient ankles demonstrated an increase of 0.9 +/- 0.5 mm in anterior translation (P = .008), an increase of 5.7 degrees +/- 3.6 degrees in internal rotation (P = .008), and a slight increase of 0.2 +/- 0.2 mm in the superior translation (P = .02) relative to the intact contralateral ankles.

Conclusion: Deficiency of the ATFL 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 so provide a baseline for improving ankle ligament reconstructions aimed at restoring normal joint motion.

Figure 1

3D models of the tibia and talus were created from high-resolution MR images (upper left). The patient then stepped onto a level surface with increasing body weight while being imaged using orthogonal fluoroscopy (upper right). The 3D models of the tibia and talus were manipulated in 6 degrees-of-freedom until their projection matched that of the orthogonal fluoroscopic images (bottom).

Figure 2

Radio-opaque markers were implanted into a cadaver for a validation study. The accuracy of the system in measuring tibiotalar kinematics was within 0.04 ± 0.11mm and 0.2±0.1°.

Figure 3

Weight-bearing loads caused an anterior translation in both the intact and ATFL deficient ankles. Statistically significant increases were observed in the deficient ankle compared to the intact ankle (* p < 0.05).

Figure 4

Weight-bearing loads caused a lateral translation of the talus in both the intact and ATFL deficient ankles. No statistically significant differences were detected.

Figure 5

Weight-bearing loads caused a superior translation of the talus relative to the tibia. At 100% body weight, a statistically significant increase in superior translation was observed in the ATFL deficient ankle (*p < 0.05).

Figure 6

ATFL deficient caused a statistically significant internal rotation of the ATFL deficient ankle relative to the intact ankle (*p < 0.05).

Figure 7

Weight-bearing loads caused an eversion of the talus. No statistically significant differences were observed between intact and ATFL deficient ankles.

Figure 8

Increasing weight-bearing loading caused an increase in dorsiflexion of the talus. No statistically significant differences were observed between the intact and ATFL deficient ankles.

Figure 9

The oblique orientation of the anterior talofibular ligament in the transverse plane suggests that it resists the anterior translation and internal rotation of the talus. (A = Anterior, P = Posterior)

Figure 10

Increased internal rotation may lead to increased cartilage loading on the medial side of the talus, due to the curved surface of the cartilage on the medial portion of the tibia.