Metatarsal fractures are common. Since all five metatarsals function differently, they all require different treatments. They are divided into three sections - 1st, 5th, and 2nd - 4th. The most common mechanisms of injury are either direct impact, such as a crushing injury, causing a transverse or comminuted fracture pattern, or twisting-type injury causing an oblique fracture pattern with soft-tissue swelling. Chronic direct forces can produce stress fractures. Avulsion can occur especially at the base of the 5th metatarsal.
The first metatarsal is wider, shorter, stronger, and more mobile than the others. Two sesamoid bones under the head of the 1st metatarsal bear approximately 1/3 of the body weight. The anterior tibialis attaches to the inferomedial base functioning in elevation of the 1st metatarsal and supination of the forefoot. Peroneous longus attaches on the proximal lateral base functioning in plantar flexion of the first metatarsal and pronation of the forefoot. There are no interconnecting ligaments between the 1st and 2nd metatarsal allowing for independent motion. Injuries to the 1st metatarsal are usually due to direct trauma and are often open or comminuted. The dorsalis pedis artery and deep peroneal nerve are in this area and branches of the superficial peroneal nerve are around the deeper structures and must be protected during surgery.
The 5th metatarsal has tendinous attachments of the peroneus brevis and tertius, and attachment of the plantar aponeurosis. Fractures of the 5th metatarsal account for approximately 25% of all injuries to the metatarsals, including basilar or avulsion fractures, metadiaphyseal (Jones) fractures, metadiaphyseal stress fractures, and diaphyseal fractures. Blood is supplied from a single artery that enters at the junction of the proximal and middle thirds of the diaphysis and supplies the shaft. Secondary arteries supply the base and the tuberosity. Damage to the sural nerve which is also present in the surgical area should be avoided.
The Orthopedic Trauma Association uses the format [81( ) - _ _._] to classify metatarsal fractures. The parenthesis holds a letter corresponding to a metatarsal as follows:
- T = 1st metatarsal
- N = 2nd metatarsal
- M = 3rd metatarsal
- R = 4th metatarsal
- L = 5th metatarsal
The first blank holds a letter corresponding to fracture complexity:
- A = extraarticular and simple diaphyseal wedge fracture
- B = partial articular and diaphyseal wedge fracture
- C = complex articular or diaphyseal fracture
The second blank holds a number indicating the involved area:
- 1 = proximal metaphyseal
- 2 = diaphyseal
- 3 = distal metaphyseal
The third and fourth blanks hold numbers that indicate fracture patterns and they vary depending on the group and the first number.
The 5th metatarsal is divided into 3 zones based on location of the fracture:
- Zone 1: The base of the 5th metatarsal. Commonly see avulsion fractures.
- Zone 2: Fracture of the proximal metaphyseal-diaphyseal junction, also called a Jones fracture. Results from adduction or inversion of the forefoot.
- Zone 3: Proximal diaphyseal stress fractures
Patients present with pain, dorsal swelling and tenderness over the fracture site. Assessment of each metatarsal can be performed by palpating the shaft, TMT joint, and axial loading of each toe. Assessment of neurovascular status should be performed. AP and lateral weight-bearing x-rays should be obtained. MRI and technetium bone scan can assist in diagnosis of occult stress fractures.
Other associated injuries to the foot may also be present, so initial x-ray should include the whole foot.
For the 1st metatarsal, stress x-ray can help determine whether treatment should be operative or nonoperative. Nondisplaced or minimally displaced fractures can be treated with a short leg cast or removable boot gradually increasing weight-bearing over 4 weeks. Active and passive motion exercises are helpful. Operative treatment is indicated if there is any evidence of instability or loss of normal position of the metatarsal head. Choice of operative treatment depends on the configuration of the fracture. Options include closed reduction with percutaneous K-wire fixation or ORIF. Severely comminuted fracture not able to be fixed with lag screws may be treated with external fixation.
Treatment of the 5th metatarsal depends on the zone of injury. Zone 1 injuries and distal fractures can be treated closed. Treatment of acute injuries of Zone 2, the proximal diaphysis, is controversial and can range from short leg casting to surgery. Zone 3 injuries distal to the proximal tuberosity require more aggressive treatment. Zone 3 injuries have a higher incidence of nonunion. Non weight-bearing and casting is effective in some cases. Surgery should be reserved for nonunion.
Possible complications of injury and treatment of the 1st metatarsal include malunion, nonunion, arthritic degeneration of the tarsometatarsal and metatarsophalangeal joints. If shortening of the 1st metatarsal occurs, transfer metatarsalgia can occur in the other toes. A second surgery may be necessary to realign or bone graft the fracture.
Complications are rare in 5th metatarsal injuries and treatment. In Zone 1 fractures, asymptomatic nonunion can occur but usually doesn't require intervention. Sural nerve entrapment can occur. Tarsometatarsal joint pain can occur with nonunion. Nonunion of Zones 2 and 3 are due to the treatment. Immobilized non-weight-bearing helps to minimize complications. Failures are due to resumption of activity too early, inadequate bone grafting, or incomplete debriedment of the sclerotic medullary canal.