Stress Fractures

A stress fracture is an overuse injury in which repetitive submaximal loading causes focal failure of bone that cannot remodel fast enough to cope.

Up to 95% occur in the lower limb, most often the tibia and metatarsals. Low-risk sites usually heal with modified loading; high-risk sites are prone to delayed union, non-union or completing, and need specialist management.

Recognising a high-risk site is the key clinical skill. Assess relative energy deficiency in sport (REDs) in every athlete with a bone stress injury.

Bone remodels under load: osteoclastic resorption precedes osteoblastic formation, leaving a window when bone is more porous and microdamage accumulates.

Bone stress injury is a continuum: stress reaction (oedema on MRI, no fracture line), then stress fracture (a fracture line), then complete fracture. Fatigue fractures are abnormal load on normal bone, typical in athletes and recruits; insufficiency fractures are normal load on abnormal bone, as in osteoporosis, REDs or corticosteroid use.

• •Low-risk sites: posteromedial tibia, 2nd to 4th metatarsal shafts, fibula, calcaneus and pubic rami
• •High-risk sites: femoral neck (tension side), anterior tibial cortex, navicular, proximal 5th metatarsal, medial malleolus, patella, talus and great toe sesamoids

High-risk sites share high tensile load and a poorer blood supply; site matters more for management than MRI grade. Female sex and a previous stress fracture are the best-supported risk factors in runners; others include a rapid rise in training load, low energy availability, low vitamin D and smoking.