A 28 year-old otherwise healthy male presented to the emergency department with left foot pain. He was walking his dog when the leash became tangled in his legs, causing his left foot to be pulled while plantarflexed. He noted an acute onset of lateral foot pain and has been having difficulty bearing weight ever since.
It is estimated that approximately 5-6% of fractures seen in the primary care setting are metatarsal fractures, with the 5th metatarsal being the most commonly fractured metatarsal at 68%. 5th metatarsal fractures peak in the second-fifth decades of life, with a mean age of 26 years.
The 5th metatarsal has three joints associated with it; the cubometarsal joint and intermetarsal joint proximally as well as the metatarsophalangeal joint distally. The peroneus brevis tendon and the aponeurosis of the plantar fascia attach to the tuberosity of the base of the 5th metatarsal and the peroneus tertius inserts dorsally onto the metadiaphyseal junction. The blood supply is primarily supplied by the metaphyseal perforating arteries proximally and distally with the remainder supplied by the nutrient artery and periosteal blood supply as detailed below in image 5. The watershed that is created by the metaphyseal arteries and the nutrient artery plays a significant role in impeding the healing of fractures in this area.
History can help lead to the diagnosis based on the mechanism. Patients will present with lateral foot pain, typically acute in onset with or without a prodrome of pain in the affected area. For Zone I injuries ( see classifications below), injuries usually occur during supination with plantar flexion, causing pulling from the lateral band of the plantar fascia on the tuberosity. Zone II injuries usually occur during plantar flexing of the forefoot. Zone III injuries are usually due to repetitive trauma such as running and jumping.
Three standard plain radiograph views of the foot are recommended for initial evaluation; the AP, lateral, and 45 degree oblique. In the setting of complex trauma, CT scan is recommended to evaluate for concomitant Lisfranc injury. Plain radiographs typically will not show acute stress fracture; radiographs 10-14 days post injury are recommended for evaluation of this. MRI can show stress injury or incomplete stress fracture. It is prudent to not confuse os peroneum, an ossicle residing in the peroneus longus tendon, for a 5th metatarsal avulsion fracture. This can be confused due to the location of the os peroneum just proximal to the 5th metatarsal.
5th metatarsal fractures are divided into proximal and distal fractures. The classification of the proximal fractures is more controversial. The Torg classification was proposed to differentiate proximal fractures based on healing potential, as metadiaphyseal junctional fractures are less likely to heal due to watershed area of the blood supply between the metaphyseal
perforators and the nutrient arteries (see image 5). The classification most commonly used today is the Lawrence and Botte classification. Using this classification, Zone I fractures are avulsion fractures of the tuberosity, Zone II fractures (aka Jones fracture) are acute fractures at the junction of the metaphysis and diaphysis, and zone III fractures are stress fractures at the proximal diaphysis. Practically speaking, Zone II and III fractures share a similar tenuous blood supply which can negatively affect healing. Distal diaphyseal fractures are known as dancer’s fractures due to their frequency in high performance dancers.
The management varies based on fracture type and individual patient fractures. Nondisplaced zone I fractures are treated with a CAM boot with weight bearing as tolerated. If displaced more than 3 mm or greater than 30% of the cubometatarsal joint, operative treatment is considered. For Zone II and III fractures, non-displaced fractures can be managed non-operatively with immobilization and non-weight bearing initially for 6-8 weeks followed by progressive weight bearing. Operative management is considered in athletes due to less prolonged immobilization, non-union, refractures, and a cavovarus foot due to the likelihood of refracture. Most neck and shaft fractures can be treated non-operatively with a CAM boot and weight bearing as tolerated. Operative treatment is considered for greater than 10 degrees of plantar angulation or 3-4 mm of translation in any plane if closed reduction fails.