Metatarsal Stress Fractures

A metatarsal stress fracture is a bone stress injury from repetitive loading, most often of the 2nd or 3rd metatarsal, seen in runners, military recruits, dancers and impact-sport athletes.

The key distinction is between low-risk and high-risk sites:

• •Low risk: 2nd to 4th metatarsal shafts, which usually heal with modified loading
• •High risk: the proximal 5th metatarsal (Jones zone and proximal diaphysis) and the base of the 2nd, which are prone to delayed union and non-union

A normal X-ray does not exclude a stress fracture. Assess for Relative Energy Deficiency in Sport (REDs) in any athlete with a bone stress injury.

The 2nd and 3rd rays are the stiffest and take about 90% of metatarsal stress fractures, most at the distal shaft and neck. Fractures at the base of the 2nd, seen in ballet dancers, are more prone to non-union.

The proximal 5th metatarsal has 3 zones:

• •Zone 1, tuberosity: avulsion fractures from an inversion injury. Low risk and not a Jones fracture
• •Zone 2, metaphyseal-diaphyseal junction: the Jones fracture zone, at a vascular watershed with a high non-union risk
• •Zone 3, proximal diaphysis: the typical site of 5th metatarsal stress fractures in athletes, also high risk

Bone stress injury is a continuum from stress reaction (oedema, no fracture line) to stress fracture to complete fracture. Fatigue fractures are abnormal load on normal bone; insufficiency fractures are normal load on abnormal bone (osteoporosis, rheumatoid arthritis, corticosteroids).

Risk factors:

• •A rapid increase in training volume or intensity
• •Previous stress fracture and female sex, the 2 risk factors best supported by evidence
• •REDs, low vitamin D, smoking, tight gastrocnemius, a cavus foot and a recent change of shoe