Articular surface of the talocrural joint
The talocrural joint is a very important anatomical joint, consisting of an elaborate square-shaped articular cavity formed by the pulley (ceiling) of the talus bone and its two sides, and the distal end of the shin bone and its medial and lateral malleolus.
The characteristic structure of this joint is very similar to the wood joint found in traditional woodworking, giving it the unique anatomical name of ‘mortise’. The concave structure at the proximal end of the mortise is held in place by several connective tissues that firmly connect the shin and calf bones, and this characteristic concavity is a key component of the ankle joint's natural stability.
The anatomy of the mortise must be stable enough to effectively accommodate and distribute the various forces that occur between the lower limb and foot during everyday activities such as walking, running, and jumping.
Noteworthy from this biomechanical perspective is that compressive forces are unevenly distributed within the joint. Approximately 90-95% of the total load is transmitted through the articular surface between the talus and tibial bones, with only 5-10% being transmitted through the lateral parts of the talus and fibular bones.
To facilitate this load transfer, the talocrural joint is covered with a specialised articular cartilage approximately 3 mm thick, which has the remarkable adaptability to be compressed to 30-40% of its thickness under maximum physiological loading. This sophisticated load-absorbing mechanism effectively protects the subchondral bone from excessive impact or stress.
The characteristic structure of this joint is very similar to the wood joint found in traditional woodworking, giving it the unique anatomical name of ‘mortise’. The concave structure at the proximal end of the mortise is held in place by several connective tissues that firmly connect the shin and calf bones, and this characteristic concavity is a key component of the ankle joint's natural stability.
The anatomy of the mortise must be stable enough to effectively accommodate and distribute the various forces that occur between the lower limb and foot during everyday activities such as walking, running, and jumping.
Noteworthy from this biomechanical perspective is that compressive forces are unevenly distributed within the joint. Approximately 90-95% of the total load is transmitted through the articular surface between the talus and tibial bones, with only 5-10% being transmitted through the lateral parts of the talus and fibular bones.
To facilitate this load transfer, the talocrural joint is covered with a specialised articular cartilage approximately 3 mm thick, which has the remarkable adaptability to be compressed to 30-40% of its thickness under maximum physiological loading. This sophisticated load-absorbing mechanism effectively protects the subchondral bone from excessive impact or stress.
Ligament
The thin joint capsule encompassing the entirety of the talocrural joint is reinforced with various supportive structures to enhance its structural stability. Notably, laterally, the joint capsule is strengthened by collateral ligaments, which play a crucial role in maintaining the stability between the talus and the precise rectangular "socket" configuration formed by the mortise.
On the medial side of the talocrural joint, the medial collateral ligament, commonly referred to as the deltoid ligament due to its characteristic triangular shape, occupies a broad area and possesses the unique ability to elastically stretch under specific conditions.
Anatomically, the apex of the deltoid ligament is firmly attached to the medial malleolus, while its base radiates outward in a fan-like pattern through three distinct superficial fiber bundles. Deeper within, the tibiotalar fibers are intricately interwoven, effectively reinforcing the medial joint capsule of the talocrural joint.
Due to its structural features, the deltoid ligament performs critical functions, primarily restricting excessive eversion movements across the talocrural joint, subtalar joint, and talonavicular joint. The ligament's robust structural integrity, combined with additional support provided by the lateral malleolus, contributes to the relative rarity of deltoid ligament sprains.
On the medial side of the talocrural joint, the medial collateral ligament, commonly referred to as the deltoid ligament due to its characteristic triangular shape, occupies a broad area and possesses the unique ability to elastically stretch under specific conditions.
Anatomically, the apex of the deltoid ligament is firmly attached to the medial malleolus, while its base radiates outward in a fan-like pattern through three distinct superficial fiber bundles. Deeper within, the tibiotalar fibers are intricately interwoven, effectively reinforcing the medial joint capsule of the talocrural joint.
Due to its structural features, the deltoid ligament performs critical functions, primarily restricting excessive eversion movements across the talocrural joint, subtalar joint, and talonavicular joint. The ligament's robust structural integrity, combined with additional support provided by the lateral malleolus, contributes to the relative rarity of deltoid ligament sprains.