The foot is composed of 33 joints that all work together to bear weight and allow for locomotion and transmit force. Foot anatomy is divisible into the hindfoot, mid-foot, and forefoot. The hind foot is composed of the four bones the talus, calcaneus, the navicular and the cuboid. The talus has an anterior, middle, and posterior facet that articulates with the calcaneus inferiorly to form the subtalar or talocalcaneal joint. The talus articulates with the navicular distally, and the calcaneus articulates with the cuboid. The four bones of the hindfoot function together and are responsible for inversion and eversion. Some dorsiflexion and plantar flexion occur through these articulations as well. The talonavicular joint is a highly congruent ball and socket joint formed by the convex anterior margin of the talar head and the concave posterior contour of the navicular. The calcaneocuboid joint is a condyloid joint formed by the vertically oriented concave anterior facet of the calcaneus and the transversely oriented posterior convexity of the cuboid. The talonavicular and calcaneocuboid joints are also known as Choparts joints. Because of the shape and orientation of the talonavicular joint, it is responsible for the majority of the motion of the hindfoot. The talocalcaneonavicular joint, known as the acetabulum pedis, along with the calcaneocuboid joint allows for motion in both the longitudinal and transverse planes.
The midfoot is composed of five irregular shaped bones including the medial cuneiform, middle cuneiform, and lateral cuneiform and connects to the hindfoot via the mid-tarsal joint, also known as the Lisfranc joints. The Lisfranc joint is a complex articulation involving the anterior margins of the cuboid and three cuneiform bones with their respective metatarsals, none more important than the articulation between the middle cuneiform and second metatarsal base. The Lisfranc joints are gliding joints and make up the transverse arch of the foot, and its contiguity is paramount for the stability of the foot during ambulation.
The forefoot contains five metatarsals and three phalanges for each of the toes except the big toe which contains two and connects to the mid-foot through the tarsometatarsal joint. The remaining forefoot is composed of metatarsophalangeal and interphalangeal joints. Each toe possesses a proximal and distal interphalangeal joint while the great toe only has one interphalangeal joint.
The joints of the foot have two essential roles including weight bearing and propulsion during walking, running and jumping. The foot requires a high degree of flexibility and stability to be able to perform these functions. The vast number of joints in the foot are what provides this flexibility while stability results through the articulation of the joints and the ability of the foot to go from a rigid level to a flexible lever to a rigid lever during the normal gait cycle. The midtarsal joint plays a role during ambulation, and its function is dependent on the position of the subtalar joint. During eversion of the subtalar joint, the talonavicular and calcaneocuboid joints are parallel to each other and permit motion between them. This motion is important during the early stance/heel strike stage of ambulation. Conversely, with inversion of the subtalar joint, the joints are not parallel, and no motion is permitted allowing the foot to act as a rigid lever for the late stand/toe-off phase of ambulation. Metatarsal phalangeal joints are condyloid joints that allow for flexion and extension as well as abduction and adduction. Interphalangeal joints are hinge joints allowing for flexion and extension.
The blood supply to the foot comes mainly from the dorsalis pedis and the posterior tibial arteries. The blood supply to the joints of the foot comes from these arteries sharing anastomosis around the joints. The articular capsule is avascular and receives nutrients from the surrounding blood supply via diffusion.
Fractures and Dislocations:
Lisfranc injuries are categorizable into sprains and fracture/dislocation. The most common mechanism of injury is axial compression on a hyper-plantar flexed foot. Patients present with a painful swollen foot with inability to bear weight. Patients also typically have a plantar ecchymosis at the mid-foot which is highly correlative to a Lisfranc injury. During the physical exam, there is palpable tenderness at the mid-foot, and passive motion of the forefoot reproduces the pain. Initial imaging is done with non-weight-bearing AP, lateral and oblique x-rays. This can miss up to 50% on injuries so if there is a high index of suspicion then a weight-bearing comparison film with contralateral foot is helpful.
Disruption of a line drawn from medial base of the second metatarsal to the middle cuneiform as well as dorsal displacement of the first and or second metatarsal bases are reliable signs of fracture dislocation. Two mm or more of separation between the first and second metatarsal is a sign of instability. The fleck sign is another important finding of a Lisfranc injury and indicates an avulsion fracture of the Lisfranc ligament from the 2nd metatarsal base. Missed diagnosis is common for Lisfranc injuries and can lead to chronic pain, dysfunction, and deformity. Non-displaced injuries are treated with a non-weight-bearing cast or boot for 6-8 weeks. If the injury is displaced over two millimeters then surgical fixation is required. For markedly displaced injuries open reduction and internal fixation is the treatment of choice.
Calcaneus fractures are result axial load secondary to a fall from a height. The range of injuries can be mildly displaced to severely comminuted fractures. Often missed injuries also include lumbar spine compression fractures. These injuries can be devastating in their long-term sequelae not only from the damage to the subtalar joint but to the surrounding soft tissue as well.
Jones fractures are fractures of the base of the fifth metatarsal separate and distinct from avulsion fractures. This fracture represents a vascular watershed area prone to nonunion and requires prompt surgical stabilization.
Charcot Neuropathic Osteoarthropathy:
Charcot neuropathic osteoarthropathy is a chronic progressive disease most commonly seen in diabetes. This is frequently seen in the foot and ankle as a result of peripheral neuropathy. It starts off as a localized unregulated inflammatory process but eventually leads to gradually bone loss, joint dislocations, and deformities. Patients usually present with a red, warm and swollen foot. Pain may or may not be present. Radiographs of the affected area can show a range of pathologies from osteopenia, fracture and dislocations, and severe joint destruction. Work up should include a CBC, CRP, ESR to rule out an infectious process. Bone scan and MRI are also helpful. MRI may help distinguish between infection and arthropathy.
Gout typically presents as an acute and extremely painful red, swollen great toe specifically affecting the metatarsophalangeal joint (MTP). The pathogenesis remains unclear but is thought to be due to a purine metabolism defect causing monosodium urate crystals to deposit in joints. Patients usually have elevated uric acid in the blood but diagnosis is made by aspiration of the joint to find negatively birefringent crystals. Treatment for acute episodes is rest with nonsteroidal anti-inflammatory medications, glucocorticoids, or colchicine. Allopurinol or other a xanthine oxidase inhibitors are used to prevent future occurrences. Additionally, conservative treatment such as weight loss, avoiding purine rich food and alcoholic beverages, are adjunctive measures to help alleviate symptoms.
Hallux rigidus is a degenerative joint disease of the MTP joint of the great toe. Patients typically present with a painful stiff toe with tenderness to palpation of the MTP joint dorsally. Osteophytes may be palpable dorsally on the physical exam. The most common physical exam finding is usually a decrease in active and passive range of motion, most notably dorsiflexion. On x-ray there is the characteristic dorsal osteophyte and signs of osteoarthritis of the 1st MTP. Treatment includes NSAIDs, activity and shoe modification and intra-articular injections. It can also be treated surgically.
Hallux valgus is valgus deviation of the proximal phalanx which promotes varus posturing of the first metatarsal. The metatarsal head is displaced medially leaving the sesamoids uncovered. The medial capsule becomes attenuated and the lateral joint capsule is contracted. Risks factors are both intrinsic and extrinsic. There is a genetic predisposition in addition to biomechanical factors related to the first ray that may lead to bunion deformity. High-heeled shoes with a narrow toe box can also lead to deformity. Bunions are more common in adults, primarily women, but are also common in children, termed juvenile hallux valgus. Patients present complaining of pain exacerbated by shoe wear. Physical examination reveals a wide forefoot with tenderness over the first metatarsal head and a valgus deviation of the phalanx. Conservative treatment consists of shoe modification and the avoidance of high-heeled footwear. Juvenile hallux valgus should be treated conservatively as long as possible. Patients who fail conservative treatment may be treated surgically. Surgical treatment depends of the deformity.
Lesser Toes Deformities:
Claw toes are hyperextension deformities of the MTP joint with a flexion deformity of the PIP and the DIP. Hammertoes are flexion deformities of PIP and extension deformities of the MTP and DIP joints. Mallet toes are flexion deformities of the DIP joints. If any of these deformities become symptomatic, then they can be treated conservatively with splinting/padding or for severe deformities surgical management.