THE BIG FOOT BOGEY: Base of 5th metatarsal fracture

THE BIG FOOT BOGEY: Base of 5th metatarsal fracture

(By Simon Bartold)

There has always been confusion about fractures of the base of the 5th MT. Often all fractures in this region are labeled ‘Jones fractures’, and this is problematic, because a Jones fracture is a serious sports medical issue, and very removed from a straightforward stress fracture or cortical fracture of the MT shaft.
Fractures of the 5th metatarsal command attention, both for their often complex nature and the confusion existing over their classification. The least common fracture of the 5th metatarsal is the acute spiral fracture of the base and diaphysis, usually sustained after a fall or severe inversion injury with superimposed load. These fractures usually heal uneventfully, dependent upon displacement and rotation, and are managed with a weight bearing below knee cast. The remaining fracture of the 5th metatarsal have perhaps been best classified by Lawrence and Botte. They described three distinct fracture types around the proximal 1/3rd of the 5th metatarsal;
• The Jones’ fracture at the junction of the metaphysis and diaphysis.
• The diaphyseal stress fracture.
• The tuberosity avulsion fracture.
There has been considerable confusion in the separation of these fractures from each other, with, in particular, all proximal fractures labelled Jones’ fractures by some practitioners. This practice is risky at best since all these fractures have quite distinct natural histories and do require individual management strategies.

Anatomical Considerations
The proximal 1/3rd of the 5th metatarsal has significant attachments from major tendons and ligaments, including the tendons of peroneus brevis, peroneus tertius, adductor digiti minimi, the interossii and the lateral band of the plantar fascia.

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In addition, the 5th metatarsal has a strong association with the cuboid and 4th metatarsal. All these structures are important in resisting dislocation of the base of the 5th metatarsal. However, sporting activities involving pivoting whilst on the ball of the foot may especially render the base of the 5th metatarsal to injury. The region is further compromised by the fact that the 5th metatarsal base is mostly cancellous bone with very thin cortices.
Because cancellous bone is well vascularised, fracture in this region generally heals well, however, more distallyat the junction of the proximal metaphysis
and diaphysis, bone architecture and vascularity change. In this zone, there is a change in the ratio of cancellous bone to cortical bone, with marked narrowing of the medullary canal and cortical thickening.

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This then creates an area of relative avascularity which heals very poorly after fracture. A fracture in this region is a true Jones’ fracture and was described by the English physician Sir Robert Jones in 1902. In fact, Jones sustained the injury he described whilst attending a military dance. Jones’ fractures are typically located about 1.5 – 2 cm from the proximal end of the 5th metatarsal. They result from vertical and mediolateral forces, often with the foot in plantarflexion and the forefoot adducted. The transversely oriented fracture will occur, which should be differentiated from stress fractures of the diaphyseal shaft.
Jones’ fractures are imaged with plain anteroposterior and especially oblique views which will help visualise the position of the fracture. Jones’ fractures occur in cutting sports like football and basketball, and maybe a sequelae of acute ankle inversion injury. Jones’ fracture has very reputation for slow healing or non-union secondary to the poor blood supply in this region. However, if the lesion is identified early prior to cortical and intramedullary sclerosis and treatment is optimal, conservative management can be very successful. Initial management involves four to six weeks non weight bearing immobilisation with an additional four weeks in a weight bearing below knee cast. Patient compliance is critical, especially in the strict non weight bearing phase of treatment.
Clapper et al (1995) recommend aggressive surgical management of Jones’ fractures in professional athletes to allay the risk and downtime of a non-union. Likewise, any patient not responding to conservative management should be referred for surgery, which most commonly involves percutaneous insertion of a cannulated screw, positioned longitudinally down the intramedullary canal (Brukner et al 1999). This surgery achieves excellent results and rapid return to activity within four to eight weeks is expected.

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True Jones fracture through the junction of the proximal metaphysis and diaphysis.
A pseudo Jones Fracture.
Typical non-union of a Jones fracture. Note sclerotic margins at non-union.

Avulsion Fracture of the 5th Metatarsal Tuberosity

This transversely oriented avulsion fracture of the base of the 5th metatarsal is the most common of all 5th metatarsal fractures and amongst the most common of all foot fractures in children. Owen et al (1995) reported that of a series of 69 foot fractures, 45% were 5th metatarsal avulsion fractures.

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Typical avulstion fracture of the base of the 5th metatarsal. This fracture shouldNOT be confused with a Jones Fracture

Avulsion fracture of the 5th metatarsal is caused by a sudden forceful pull of the tendon of peroneus brevis in acute inversion ankle injury. The lateral fibres of the plantar aponeurosis are also implicated in this injury in plantarflexion and inversion. It’s important to discriminate between this injury and the presence of a normal unfused apophysis which has a longitudinal orientation and is located laterally, at the base of the 5th metatarsal. See figure 9.17. Avulsion fractures usually heals well secondary to an abundant blood supply. A short period of non-cast immobilisation is usually sufficient.

Stress Fractures of the Diaphyseal Shaft

Torg and co-workers (1984) classified stress fractures of the diaphyseal shaft of the 5th metatarsal as acute, delayed union or non-union.
Torg type 1 fracture is an acute fracture of the 5th metatarsal without pain. Radiographically there is periosteal reaction of the fracture site with no medullary sclerosis. Brukner et al (1999) recommend immoblisation in below knee non weight bearing cast for six weeks followed by careful review on cast removal. Torg type II diaphyseal fracture is an acute and painful stress fracture aggravated by activity. Radiographs will expose the fracture with cortical thickening and medullary sclerosis. These fractures are subject to delayed or non-union and as such surgical repair with percutaneous screw fixation may be the most expedient avenue of treatment.
An established radiological non-union of a 5th metatarsal fracture is called a Torg type III fracture. In this instance there is obvious fracture with complete obliteration of the medullary canal. These fractures are treated aggressively with intramedullary screw fixation and/or bone grafting. Return to sport from this injury is slow and careful follow up monitoring is essential.

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