Bone



Bone


Marlon J. Murasko

Erin S. C. Harris



BONE

The 26 bones that comprise the skeletal structure of the foot and ankle work in concert as a complex load-bearing machine. It is essential to human’s ability to sustain bipedal ambulation. A multitude of osteoligamentous structures comprise the ankle, hindfoot, midfoot, and forefoot and constitute the bony anatomy of the foot and ankle.


ANKLE

The ankle joint is the talocrural joint, a highly conforming hinge joint between the tibiofibular mortise and the talar dome. The distal articular surface of the tibia, or tibial plafond, is concave in the sagittal plane and convex in the coronal plane. This duality helps to maintain tight conformity of the articular surface between the tibia and the talus throughout the flexion arc. Perfect conformity of the ankle joint is essential to minimize joint contact forces—displacement of the talus within the tibia by 1 mm increases peak joint contact forces by 50%.

The mortise of the ankle joint is comprised of the tibia and fibula whose spatial relationship is maintained by the inferior tibiofibular syndesmotic joint, or syndesmosis, which comprises five ligamentous structures: the anterior inferior tibiofibular ligament, posterior inferior tibiofibular ligament, transverse tibiofibular ligament, interosseous ligament, and interosseous membrane. The distal fibula lies posterolateral to the tibia in a notch. Minimal motion occurs at the point of contact. The surface of the distal tibia and the talar dome are both wider anteriorly than posteriorly. As the foot is dorsiflexed, the talus fits more tightly into the mortise and applies a laterally directed force to the fibula. The distal fibula and the medial process of the tibia—the lateral and medial malleoli articulate with the lateral and medial sides of the talar dome, providing additional stability to the joint.

Ankle stability is conferred by joint congruity and ligamentous support from collateral ligaments. The medial sided collateral ligaments exist as a coalescent triangular structure referred to as the deltoid ligament, which encompasses the superficial deltoid fibers and the deep deltoid fibers. The superficial deltoid fibers consist of the talonavicular ligament, tibiocalcaneal ligament, and posterior tibiotalar ligament. The deep deltoid, the primary medial stabilizer, comprises the anterior tibiotalar ligament. The lateral collateral ligaments of the ankle consist of the anterior talofibular ligament, posterior talofibular ligament, and calcaneofibular ligament.


HINDFOOT

The talus and calcaneus make up the hindfoot, and the three facets by which they articulate comprise the subtalar joint—anterior, middle, and posterior. The posterior facet, termed the talocalcaneal joint, is the largest and is the principal weight-bearing facet during standing.
The anterior facet partly constitutes the talocalcaneonavicular joint complex. Direct ligamentous constraints of the subtalar joint include the medial, posterior, and lateral talocalcaneal ligaments, the interosseus talocalcaneal ligament—which span the tarsal sinus between the posterior and middle subtalar facets, and the cervical talocalcaneal ligament adjacent to this complex. The subtalar joint is further constrained laterally by the calcaneofibular ligament and the extensor retinaculum. The fibrous capsule provides inherent stability as well.

The talus has five unique articular interfaces: the talocrural joint, including medial and lateral facets which articulate with the malleoli, the anterior, middle, and posterior facets of the subtalar joint, and the talonavicular joint. The talus is devoid of musculotendinous insertions. A large percentage of the surface area of the talus is covered by articular cartilage. Consequently, the talus has limited periosteal blood supply and is prone to avascular necrosis when subjected to trauma. Vascular supply to the talus inserts along with ligamentous insertions, at a bare area of the talar neck. It is principally comprised of the dorsalis pedis artery, sinus tarsi branches of the peroneal and dorsalis pedis arteries, the artery of the tarsal canal and deltoid branch of the posterior tibial artery, which enter the dorsal, lateral, and medial talar neck, respectively. The artery of the tarsal canal forms an important anastomosis with the artery of the tarsal sinus. Additional capsular and ligamentous branches contribute as well.

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Sep 8, 2022 | Posted by in ORTHOPEDIC | Comments Off on Bone
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