SLR - February 2011 - Rotem Ben-Ad
Reference: Kamiya, T., et al. (2009). Mechanical Stability of the Subtalar Joint After Lateral Ligament Sectioning and Ankle Brace Application: A Biomechanical Experimental Study. Am J Sports Med. 2009; 37:2451-2458.
Scientific Literature Review
Reviewed by: Rotem Ben-Ad, DPM
Residency Program: Cambridge Health Alliance; Cambridge, MA
Podiatric Relevance:
Ankle sprains are undoubtedly one of the most common lower extremity injuries encountered, especially in sports-related activities. Additionally, chronic ankle sprains are known to cause lateral ankle instability. This article states that 10%-25% of patients with lateral ankle instability also have subtalar joint instability. It is important to distinguish which ligaments have been disrupted, as well as which forces have the most damaging effect on healing. One of the mainstay treatments for ankle/subtalar joint instability has been bracing. One interesting point that the article suggests is the need to improve the design of ankle bracing. Although bracing is successful in restricting talar motion with eversion and inversion forces, the study shows that this is not necessarily the case with internal and external rotational torques. If one is able to determine that these are the primary forces affecting the patient’s subtalar joint, another method of stabilization may need to be applied.
Methods:
Ten normal fresh frozen cadaveric feet were mounted on a custom jig and fixed with pins at neutral angles. Electromagnetic sensors were attached to the talus, tibia, and all 3 dimensional movements were recorded on a computer using a magnetic tracking system. The feet were first tested with all ligaments intact. Both the angles of the subtalar and talocrural joints were measured with eversion, inversion, external rotation, and internal rotations forces applied. Serial sectioning of the calcaneofibular ligament, cervical ligament, and interosseous ligament was then performed. Measurements were taken after each sectioning. The Ever Step 6 ankle brace was applied after complete sectioning of all three ligaments and another set of measurements was taken.
Results:
Talocrural Joint: With sequential sectioning of the ligaments, the angular changes of the joint in the frontal plane were significantly increased. The largest influence was noted to be the calcaneofibular ligament, as sectioning of the next two ligaments did not create significantly increased angles. However, application of the ankle brace decreased the angular changes close to the baseline prior to sectioning. Angular changes of the talocrural joint with eversion forces, as well as external and internal rotation torques were very minimal. Subtalar Joint: In terms of application of the inversion force, sequential sectioning of the ligaments increased the angle between the talus and calcaneus in the frontal plane. The angles increased even more so with complete sectioning of the ligaments. Interestingly, there was no statistical significance between the intact state and application of the brace following complete sectioning. These same results were found with the rotational angles of the talus in the transverse plane. However, anterior motion of the talus was not significantly different between the intact state, complete sectioning, and brace application. With eversion force, there was little change in the angles of the talus. However, application of the brace significantly decreased the angle between the talus and calcaneus in the frontal plane. Application of internal rotation torque did not change the rotational angles of the joint in the transverse plane appreciably with sectioning of the ligaments. Although the brace decreased the rotational angles, the value was not statistically significant. With external rotation torque, each sequential sectioning increased the rotational angles of the subtalar joint in the transverse plane. As previously noted, there was a statistical significance between the angles in the intact ankle and of that with the ankle brace.
Conclusions:
This study demonstrated the importance of the calcaneofibular, cervical, and interosseous ligaments in the stabilization of the subtalar joint. The calcaneofibular ligament was shown to be vital in restricting excessive motion of the talus, especially with external rotation forces. This was shown by an increase in talar motion with sectioning of the calcaneofibular ligament, and even more motion after sectioning of the cervical ligament. The cervical ligament was shown to restrict excess motion of talus inversion as well as talus rotation with external rotational torques. The study indicates that application of the ankle brace considerably restricted motion of the subtalar joint with eversion and inversion forces. However, a statistically significant difference was not shown with internal and external rotational forces.