Bone Stress Injuries

Bone stress injuries (BSIs) are overuse injuries in which repetitive loading outpaces the bone's ability to remodel, giving a continuum from stress reaction to stress fracture.

They are common in runners, military recruits and dancers, most often in the tibia and metatarsals.

Low-risk sites usually heal with modified loading; high-risk sites are prone to non-union or completing and need specialist management. Every athlete with a BSI is assessed for relative energy deficiency in sport (REDs).

Bone remodels under load, and resorption precedes formation, leaving a window when bone is more porous. When loading rises faster than bone can adapt, microdamage accumulates.

• •Stress reaction: periosteal and marrow oedema on MRI, no fracture line; reversible with load modification
• •Stress fracture: a discrete fracture line within oedematous bone
• •Complete fracture: from continued loading, most dangerous at high-risk sites

Fatigue fractures are abnormal load on normal bone; insufficiency fractures are normal load on abnormal bone, as in osteoporosis or corticosteroid use.

Low-risk sites:

• •Posteromedial tibial shaft, the compression side and the commonest site
• •2nd to 4th metatarsal shafts, fibula, calcaneus, pubic rami, sacrum and femoral shaft

High-risk sites, with high tensile load or a poor blood supply:

• •Femoral neck, tension (superolateral) side: can displace, risking avascular necrosis
• •Anterior tibial cortex: the tension side, with a high non-union rate
• •Navicular: a relatively hypovascular central third
• •Proximal 5th metatarsal (zones 2 and 3): a watershed blood supply
• •Patella, medial malleolus, talus and great toe sesamoids

Previous stress fracture and female sex are the risk factors best supported in runners. Others include a rapid rise in training load, low vitamin D or calcium intake, a cavus foot and worn footwear. Low energy availability (REDs) disrupts reproductive hormones in both sexes, impairs bone formation and lowers bone mineral density.