Injuries to this ligament, so called high ankle sprains, occur when the foot is stuck on the ground while the leg rotates inwards. The posterior talofibular ligament runs from the back lower part of the fibula and into the outer back portion of the calcaneus (Figure 10). This ligament functions to stabilize the ankle joint and subtalar joint. The ligament group formed by the AITFL and the interosseous membrane, joined by the posterior inferior tibiofibular ligament, the transverse ligament and the interosseous ligament is known as the syndesmosis. Bipartite Sesamoid: This condition occurs when one of the sesamoids associates with the great toe fails to ossify resulting in two bone segments connected by a fibrous union. Os Peroneum: This extra bone is found within the peroneus longus tendon sheath at the point where it wraps around the cuboid. The superficial posterior compartment of the leg holds the two large muscles of the calf, the gastrocnemius and the soleus, which both run along the length of the leg joining to form the Achilles tendon. Os Naviculare (Os Tibiale Externum or Accessory Navicular): This bone represents a failure to unite the ossification center the navicular tuberosity (where the tibialis posterior tendon inserts) to the main center of the bone.

Bone Subfibulare: This extra bone is seen at the type of the fibula. Bipartite sesamoids are seen in about 20% of the population with more than 90% of them occurring in the tibial sesamoid. It is seen in 1-2% of the population. The calcaneofibular ligament (Figure 10) is also on the lateral side of the ankle. This ligament functions to resist eversion. The peroneus longus also functions to plantarflex the first metatarsal. This muscle compartment is located on the backside of the leg deep to the soleus muscle. There are a large number of smaller muscles deep inside the foot. The deep peroneal nerve innervates all the muscles of the anterior compartment. Both of these muscles are controlled by the superficial peroneal nerve. This keeps the metatarsals moving in sync. The first three metatarsals medially are more rigidly held in place than the lateral two. The plantar ligaments are stronger than those on the dorsal side (Figure 12 & 13). The Lisfranc ligament is a strong band of tissue that connects the medial cuneiform to the base of the second metatarsal.

Os Trigonum: Found at the posterior aspect of the talar body, this ossicle is connected to the talus via a fibrous union that failed to unite (ossify) between the lateral tubercle of the posterior process. These ligaments run between the metatarsal bones at the base of the toes (Figure 12). They connect the neck region of each metatarsal to the one next to it, and bind them together. The anterior compartment is comprised of four muscles that extend (dorsiflex) the foot and ankle (Figure 14). The Tibialis Anterior, the Extensor Hallucis Longus, the Extensor Digitorum Longus and the Peroneus Tertius. Collectively the muscles in these four compartments are referred to as the extrinsic muscles of the foot because they originate above the foot in the leg, but insert within the foot. It originates above the knee joint, off the posterior femur, and inserts into the calcaneus. It starts at the tip of the fibula and runs along the lateral aspect of the ankle and into the calcaneus. The spring ligament (Figure 11) is a strong ligament that originates on the sustentaculum tali – a bony prominence of the calcaneus on the medial aspect of the hindfoot.

The deeper branch of the ligament is securely fastened in the talus, while the more superficial, broader aspect runs into the calcaneus. This allows this ligament to stabilize the great toe on the medial side. In the situation where a person develops a bunion, this band gets stretched out, and the great toe changes position and becomes angulated outward. The gastrocnemius is the most superficial of the posterior calf muscles. Both gastrocnemius and soleus muscles are innervated by the tibial nerve. The TMT joint is made stable not only by strong ligaments connecting these bones, but also because the second metatarsal is recessed into the middle cuneiform in comparison to the others (Figure 7). The metatarsal heads are the main weight bearing surface and the site where the phalanges attached at the metatarsal-phalangeal (MTP) joint. The Lisfranc joint complex is a series of ligaments that stabilize the tarsometatarsal joints. It too resists inversion, but more when the ankle is dorsiflexed. It stabilizes the ankle against inversion, especially when the ankle is plantar-flexed. The ATFL runs from the anterior aspect of the distal fibula (lateral malleolus) down and to the outer front portion of the ankle in order to connect to the neck of the talus.