Fifth Metatarsal Fracture

Fifth metatarsal fractures are the most common metatarsal fracture, about 70% of all metatarsal fractures. The commonest pattern is avulsion of the tuberosity (the base) by the peroneus brevis tendon and the lateral band of the plantar aponeurosis during an inversion injury. The tuberosity has a rich metaphyseal blood supply, and these fractures heal reliably.

Patterns covered here:

• Tuberosity avulsion (zone 1): transverse to oblique line at the base, extra articular or entering the cuboid metatarsal joint
• Proximal diaphyseal stress fracture (zone 3): distal to the intermetatarsal joint, in the proximal shaft
• Distal shaft and neck fractures: spiral or oblique (twisting) or transverse, from a direct blow or the "dancer" mechanism of a roll over

In adolescents, a normal apophysis at the tuberosity (ages 8 to 15) lies parallel to the shaft, whereas a fracture is transverse. Complications are asymptomatic fibrous union (common in avulsions), symptomatic nonunion (under 5%), malunion with a plantar prominence, sural neuritis and chronic lateral pain.

• Lateral foot pain, swelling and bruising after an inversion injury, usually with the ability to bear weight
• Tenderness at the tuberosity, pain with resisted eversion and passive inversion
• Shaft fractures: localized tenderness along the shaft, deformity of the little toe and rotational malalignment in displaced fractures
• Stress fractures: gradual lateral foot pain with activity and tenderness along the proximal shaft, often after increased training
• Red flags: open injury, neurovascular deficit, severe displacement, multiple metatarsal fractures, and a failing stress fracture

• Radiographs (anteroposterior, lateral and oblique of the foot). Measure displacement, articular step, and the percentage of the cuboid metatarsal articular surface involved. Compare with the other foot in adolescents.
• Features that predict a poor course: displacement over 2 to 3 mm, articular involvement over 30%, sclerosis and a wide line in stress fractures.
• CT for articular detail and healing assessment.
• MRI or bone scan for early stress fractures with normal radiographs.
• Vitamin D and bone health review in stress fractures.

Differentials: lateral ankle sprain, peroneus brevis tendon rupture, normal apophysis, os peroneum fracture, cuboid fracture, midfoot sprain, calcaneal fracture.

Tuberosity avulsion, minimally displaced:

• Rigid soled shoe or walking boot with weight bearing as tolerated for 3 to 6 weeks, compression bandage, and early range of motion.
• Paracetamol 1 g orally every 6 hours with ibuprofen 400 mg orally every 8 hours with food for up to 7 days.
• Return to sport in 6 to 8 weeks.

Surgery for avulsion: displacement over 3 mm, articular surface involvement over 30% with step over 2 mm, symptomatic nonunion, or a high demand athlete. Tension band wire, 3.5 mm cortical screw or hook plate. Cefazolin 2 g IV before incision. Boot with protected weight bearing for 4 to 6 weeks.

Proximal diaphyseal stress fracture (zone 3):

• Non-weight-bearing cast for 6 to 8 weeks, then a boot.
• Early intramedullary screw fixation (5.5 to 6.5 mm solid screw) in athletes and in delayed union, with iliac or calcaneal autograft for nonunion.
• Cholecalciferol 2000 IU orally daily for 8 to 12 weeks if deficient, and calcium 1000 mg daily.

Distal shaft and neck fractures:

• Undisplaced: boot or stiff shoe with buddy taping for 4 to 6 weeks.
• Displaced over 3 to 4 mm, angulated over 10 degrees in the sagittal plane, or over 10 degrees in the coronal plane, or rotated: closed reduction and percutaneous 1.6 mm Kirschner wire fixation, or plating for unstable patterns.
• Wires are removed at 4 to 6 weeks.

Children: ibuprofen 10 mg/kg every 8 hours and paracetamol 15 mg/kg every 6 hours. Most avulsions need a boot for 3 to 4 weeks. Open physes are not violated by fixation.

Follow up at 2 weeks and 6 weeks with radiographs. Counsel on healing time and footwear.