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Ankle Biomechanics and Gait Analysis Dr. Tim Daniels MD FRCSC Assistant Professor University of Toronto Ankle Biomechanics and Gait Analysis u Anatomy and Biomechanics of the ankle joint. u Histology of ankle cartilage. u Ankle function during gait. The Ankle Joint u u u Primary motion at the ankle joint is in the sagittal plane as dorsiflexion and plantarflexion. There has been a misconception that biomechanically the ankle functions as a hinged joint Not a hinged joint. The Ankle Joint u u u Biplanar motion external rotation with dorsiflexion internal rotation with plantarflexion. 15° Ankle Rotation u u Cone shaped articulation. Rotation of the ankle joint occurs around an axis that corresponds to the position of the deltoid ligament – also referred to as the Apical Angle A A>B B Ankle Stability u A single fan shaped deltoid ligament is adequate for medial stabilization. Posterior Tibiocalcaneal tibiotalar Anterior tibiotalarligament ligament ligament Tibionavicular ligament Ankle Stability u Larger surface area laterally – stability provided by three separate bands. Anterior talofibular ligament Posterior talofibular ligament The fibula extends more distally than the medial malleolus thus providing greater osseous support on the lateral side. Calcaneofibular ligament Ankle Stability u Larger surface area laterally – stability provided by three separate bands. Anterior talofibular ligament Posterior talofibular ligament The fibula extends more distally than the medial malleolus thus providing greater osseous support on the lateral side. Calcaneofibular ligament The foot minus the talus is considered as one fibro-osseous unit. MacConaill and Basmajian 1945 Inherent stability of the ankle is important: u u It is the primary articulation responsible for the transmission of forces from the ground to the remainder of the lower extremity. It is subjected to greater forces per square cm than any other joint of the body: - FORCES CONTACT AREA Hip = 2 - 3 X body weight - 1100 mm² - Knee = 3 - Ankle = 5 - 4 X body weight - 7 X body weight - 1120 mm² - 350 mm² Ankle Stability The actual surface area of the Ankle is larger than the Knee and Hip - 12 cm² (Stouffer) The surface area available to distribute the forces is smaller = contact area The increased surface area aids in stability of the ankle joint but not in the distribution of forces. Ankle Stability The ankle joint is a stable articulation. It is supported by three bony prominences: Medial malleolus Lateral malleolus Posterior malleolus There is a common misconception that the ankle is much more stable in dorsiflexion than it is in plantarflexion The Ankle Joint Ankle Joint A 5 X body weight Foot Fulcrum B A >B The Ankle Joint A B A> > B The Ankle Joint There is a common misconception that the ankle is much more stable in dorsiflexion than it is in plantarflexion Lever Arm A >B A B The Ankle Joint u u u The ankle joint is subjected to the highest forces per square centimetre. It is more commonly injured than any other joint in the body. Yet, the incidence of symptomatic ankle arthritis is approximately nine times lower than that of the knee and hip. The Ankle Joint (Histology) Articular cartilage thickness: • Knee - 1 to 6 mm • Ankle - 1 to 1.7 mm u Ankle cartilage is more uniform in nature when compared to the knee and hip. u Ankle cartilage is stiffer than the knee and hip. u Talar cartilage is more resistant to physiologic stresses created by cyclical loading. u Ankle cartilage more resistant to the actions of MMP (matrix mealloprotinases) than the knee and hip. u Ankle Joint Function during the Gait Cycle The Foot functions as a Rocker The Ankle Joint u u u Subjected to the greatest forces. Lowest contact area. Most commonly injured joint. Remarkably resilient to the development of Osteoarthritis The ankle appears to be protected from the development of OA by its: Metabolic properties u Uniform cartilage mantle u Congruency u Stability u Restrained movement u