What it isStrong evidence
A stress fracture is a small crack in a bone from repeated load, such as running, marching or jumping, rather than one injury. Bone is always clearing old tissue and laying down new; when the load builds faster than the bone can repair itself, a crack can form.
Doctors see it as part of a scale: a stress reaction (bone under strain), then a stress fracture, then, if loading carries on, a complete break. Whether it happens depends both on the load and on how strong the bone is.
Sources 1, 2, 3, 4
Who gets itStrong evidence
Runners, people in running and jumping sports such as football and basketball, ballet dancers and military recruits. Common triggers are a sudden increase in training, a new sport, or walking long distances, especially on uneven ground, when you aren't used to it. Stress fractures make up 15 to 20% of runners' bone, joint and muscle injuries.
Weaker bones raise the risk: low bone density (osteoporosis), low calcium or vitamin D, a low body weight, and the years after the menopause. Flat feet or high arches may play a part. In a meta-analysis of runners, only two risk factors were strongly supported: a previous stress fracture (about 5 times the odds) and being female (about 2.3 times).
Sources 1, 2, 5, 6
How it's recognisedStrong evidence
Pain in one spot you can point to with a fingertip, which builds over days or weeks. At first it hurts with impact and eases with rest; later it aches even at rest or at night and is sharp with each step. Pressing on the exact spot hurts, and there may be some swelling.
An X-ray often looks normal early on, so a clear X-ray doesn't rule it out. An MRI (magnetic resonance imaging) scan is the usual next test. Bedside tests don't settle it either: in 50 people with shin pain, five common tests, including a tuning fork, a fulcrum test and pressing on the spot, all missed many stress fractures, and even the best picked up fewer than half. A review of 9 studies advised imaging instead, so a home test such as hopping can't rule one out.
Sources 1, 2, 5, 7, 8, 9, 10
Stress fracture or shin splints?Strong evidence
Both come from repeated impact, and bone stress sits on a scale, so shin pain that narrows to one spot or starts waking you at night needs checking. In one study, a third of athletes with shin splints had another lower-leg injury as well. The shin splints guide covers shin splints in detail.
- Where: shin splints hurt along a longer strip on the inner edge of the shin. A stress fracture is one spot on the bone that you can point to.
- When: shin splints hurt mostly during exercise such as running. A stress fracture builds over time, then aches at rest and at night and is sharp with every step.
- Diagnosis: shin splints can be diagnosed reliably from your story and an examination (two clinicians agreed 96% of the time). A stress fracture often needs an X-ray or another scan.
- What to do: for shin splints, stop the exercise that caused it, switch to gentle exercise and build back slowly; it usually settles within a few weeks. For a stress fracture, stop the activity and rest the bone, sometimes in a boot or on crutches, for about 6 to 8 weeks.
Sources 1, 4, 11, 12
Where it is mattersEmerging evidence
Doctors sort stress fractures into low-risk and high-risk sites. Across 76 studies of 2,974 bone stress injuries, more than 90% of athletes got back to sport, but complications were commonest at the hip, the navicular, the front of the shin bone and the base of the fifth metatarsal. The return times below are pooled averages from athletes, not a promise for any one person.
- Low risk: the back-inner edge of the shin bone, the commonest site in runners, with sport after about 44 days; the fibula, the thin outer bone of the lower leg, about 56 days; and the shafts of the metatarsals, the long bones of the foot, which one NHS fracture clinic treats in a supportive boot for up to 6 weeks.
- High risk: the navicular, on top of the midfoot, about 127 days; the base of the fifth metatarsal, on the outer edge of the foot; the front of the shin bone; and the neck of the thigh bone at the hip, about 107 days. These heal less reliably, are often kept off weight for weeks, and sometimes need surgery. For the front of the shin bone, scans are used to confirm healing before running.
- The heel bone is the second commonest site in the foot, and its pain can be mistaken for plantar heel pain (plantar fasciitis).
Sources 2, 7, 13, 14
The hip: why groin pain in a runner is urgentEmerging evidence
A stress fracture of the femoral neck, the narrow top of the thigh bone at the hip, makes up about 3% of sport-related stress fractures, mostly in distance runners. It usually causes a gradual, vague ache in the groin or front of the hip, sometimes felt in the thigh, buttock or knee, worse with running and walking and easing with rest. Turning the hip to the end of its range often hurts.
A review of these fractures in sport advises stopping weight-bearing as soon as one is suspected, with an urgent X-ray and often an MRI. Cracks on the upper (tension) side of the neck, or right across it, are usually fixed with surgery because they can shift, and a displaced fracture can cut off the blood supply to the top of the thigh bone. Undisplaced cracks caught early have had return rates as high as 100% in some series. Across all cases, though, about half of athletes don't get back to their previous level, and up to 60% after a displaced fracture.
In 123 cases pooled in another review, 71% were back to full activity at a year or more, and a sizeable share happened in people who weren't very active but had problems with their bone metabolism.
Sources 8, 15
Fuelling, REDs and bone densityEmerging evidence
Eating too little for the training you do (low energy availability) harms bone. The International Olympic Committee (IOC) calls the wider problem relative energy deficiency in sport (REDs, sometimes written RED-S), and it affects men as well as women. In 213 elite athletes assessed with the IOC's tool, those in the more severe categories had more past bone stress injuries and lower bone density, and the orange (higher-risk) category had about 7.7 times the odds of a new one over the next 6 to 24 months.
In 259 active girls and women followed over time, bone stress injuries became commoner as risk factors stacked up: 15 to 21% of those with one risk factor (12 or more hours a week of exercise, a body mass index under 21, or low bone density) had one, and 30 to 46% of those with several. The Endocrine Society suggests a bone density (DXA) scan for any adolescent or woman whose periods have stopped for 6 months or more, and sooner with severe under-eating or fragile bones.
Sources 16, 17, 18, 19
How long it takesStrong evidence
Most heal in about 6 to 8 weeks with less load; one NHS trust says about 6. Going back too early or building up too fast is how they come back, and bone stress injuries tend to recur, so the causes matter as much as the crack.
Sources 1, 4, 5