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- Overuse injuries caused by cumulative microdamage from repetitive bone loading
- Stress fractures occur in different situations:
- Fatigue fracture: abnormal stress applied to normal bone (e.g., young college athletes or new military recruits with increased physical activity demands and inadequate conditioning)
- Insufficiency fracture: normal stress applied to structurally abnormal bone (e.g., femoral neck fracture in osteopenic bone)
- Combination fracture: abnormal stress applied to abnormal bone (e.g., female long-distance runners with premature osteoporosis from female athletic triad)
- Weight-bearing bones of the lower extremity are most commonly affected at the following sites:
- Metatarsal bones
- Femoral neck
- Pars interarticularis
- Less commonly affected sites:
- High-risk stress fractures occur in zones of tension or areas with poor blood supply and are more likely to result in fracture displacement and/or nonunion. High-risk sites include the following:
- Tension side of femoral neck
- Anterior tibial diaphysis
- Pars interarticularis of lumbar spine (L4, L5)
- 5th metatarsal at metaphyseal–diaphyseal junction
- Proximal 2nd metatarsal
- Medial malleolus
- Tarsal navicular
- Talar neck
- Synonym(s): march fracture; fatigue fracture
- Greatest incidence in 15- to 27-year-olds
- Females more commonly affected than males
- Affects 9–21% of track and field athletes annually
- Up to 95% of stress fractures occur in the lower extremities (1)[A].
- Among runners, stress fractures account for 15–20% of all musculoskeletal related injuries (1)[A].
- Across all sports, the most commonly injured body sites are the lower leg (40.3%), foot (34.9%), lower back/lumbar spine/pelvis (15.2%) (2)[C].
- Occurs in <1% of general population
- Affects 5% of military recruits
- Affects 1–3% of college athletes
Etiology and Pathophysiology
- Bone is dynamic and constantly remodeling in response to applied physiologic stress.
- Repetitive loading or overuse causes microfractures that don’t heal due to imbalance between bone resorption and bone formation.
- If microdamage accumulates in excess of reparation, bony fatigue leads to stress fracture.
- Intrinsic (1)[A]
- Females are at 2.3 times higher risk than males.
- Female athlete triad (low energy availability with or without disordered eating, menstrual dysfunction, and low bone mineral density)
- History of previous stress fracture—increases risk of future stress fracture by 5 times
- History of osteoporosis, osteomalacia, rheumatoid arthritis, prolonged corticosteroid therapy
- Body composition—increased risk of stress fractures with BMI <19
- Skeletal malalignment: pes cavus, pes planus, leg length discrepancies, excessive forefoot varus, tarsal coalitions, prominent posterior calcaneal process, tight heel cords
- Biomechanical factors such as increased vertical loading rate (e.g., heel-to-toe running instead of forefoot striking)
- Muscle fatigue and decreased lean muscle mass
- Extremes of body size and composition
- Previous inactivity or low aerobic fitness
- Extrinsic (1)[A]
- Type of exercise—both male and female athletes who participate in running, track and field, cross country, and gymnastics are at highest risk (2)[C].
- Training regimen—running >32 km/week increases risk by 2 times in all athletes, by 3 times in female athletes.
- Nutritional/dietary habits—history of a diagnosed eating disorder
- Rapid increase in mileage, running pace, or training volume
- Inappropriate footwear
- Hard training surface
- Inadequate recovery or rest and training with fatigued muscle
- There is no evidence that use of oral contraceptives is related to stress fracture risk.
- Avoid abrupt increases in physical activity (no more than 10% increase in load per week).
- Reduce intensity and duration of activity if new-onset pain.
- Proper footwear
- Increasing dynamic physical activity (jumping; plyometric training) increases bone density and resistance to mechanical stress.
- Decrease vertical loading rate either by switching to forefoot strike running or (if continuing with heel-to-toe strike) by using a heel pad insert.
- Shock-absorbing foot inserts may help.
- Increased calcium and vitamin D intake may reduce stress fractures in female runners and military recruits.
Commonly Associated Conditions
- Female athlete triad
- Metabolic bone disorders