- Stress Fractures: An atraumatic partial or incomplete fracture. Can include both fatigue and insufficiency fractures.
- Fatigue fractures: Fracture due to repetitive force leading to an abnormal load on an otherwise normal bone (example: high volume of exercise stress).
- Insufficiency fractures: Fracture in abnormal bone with normal forces (examples: osteomalacia, osteoporosis).
Key Point: Classification depends upon the underlying state of the bone and the force applied.
- Bone normally responds to muscle pull (direction, intensity) or impact shock by deforming and then returning to normal shape (6).
- A complete cycle of bone turnover and remodeling and mineralization requires 3 to 4 months. When bone cannot remodel at the pace at which loading increases, the bone fractures (1).
- Wolff’s law applies to bone: As stress on bone increases, the bone deforms to accept the given force until the force exceeds bone’s elastic range, at which time permanent damage, like microfracture, occurs (3).
- Accounts for 10% of all overuse sports injuries (4).
- Running is the most commonly associated sport—accounting for 69% of stress fractures (5).
- 95% occur in the lower extremities due to dissipation of ground reaction forces during load bearing tasks such as marching, walking, running, or jumping (5).
- Typically occur in cortical bone in the following areas, in decreasing order of incidence: tibia, tarsal bones, metatarsals, femur, fibula, pelvis (3).
- Stress fractures can occur in any bone that experiences abnormal stress overload with training (scaphoid in shot putter, rib in rower, lumbar vertebrae in pitcher).
- Risk factors are many and often multifactorial. These can include both intrinsic and extrinsic elements (3–5).
- ○ Extrinsic factors include:
- ▪ Intensive training regimen/variables
- ▪ Improper or worn-out footwear
- ▪ Hard training surface
- ▪ Type of sport—e.g., running > swimming
- ▪ Low vitamin D and/or calcium intake
- ▪ Muscle fatigue (neuromuscular hypothesis)
- ○ Intrinsic factors can include:
- ▪ Low bone density
- ▪ Sex: female > male
- ▪ History of stress fracture
- ▪ Hormonal status: late menarche (>15 years of age), oligo or amenorrhea
- ▪ BMI < 19
- ▪ Low energy availability and/or eating disorder
- ▪ Systemic medical conditions that affect metabolic and/or nutritional status, such as thyroid dysfunction
Important Differential Diagnoses (4,5)
- Insufficiency stress fracture
- Medial tibial stress syndrome
- Chronic exertional compartment syndrome
- Tumor/underlying bony process other than stress fracture
- Nerve and/or arterial entrapment
- Surrounding soft tissue pathology (tendons, ligaments, muscles, bursa)
- Sickle cell disease
- Thorough history including chief complaint, associated symptoms, timing, training regimen and sport and any changes or adjustments prior to onset of symptoms, diet, risk factor assessment, medical history, medications, review of systems.
- Presentation: Typically presents with insidious onset without known trauma or injury. Pain occurs with activity and is relieved with rest. Point tenderness with palpation and the single leg hop test often reproduces pain. Femoral neck stress fractures may be worsened by performing a femoral log roll test. Fulcrum testing of the long bones also can elicit pain (3–5).
- Imaging: plain radiographs are first-line but are often negative with a sensitivity of only 10% in the early stages. If X-rays are negative but diagnosis is in question, MRI is recommended as second-line imaging modality with a sensitivity of 100% and specificity of 85% (4).
- Laboratory tests: laboratory testing not needed for diagnosis but may assist in determining the mechanism of the fracture if questioned: serum 25 (OH)D3, calcium, phosphate, parathyroid hormone, thyroid-stimulating hormone, alkaline phosphatase, albumin, and prealbumin may be considered (5).
- Low risk stress fractures are treated with relative rest with weight-bearing restriction/activity modification until patient is symptom-free, followed by gradual return to activity as tolerated. There is no consensus on timing of return to land activity, such as running, but a range of 2 to 12 weeks is generally adopted depending on fracture location and patient risk factors (2).
- High-risk stress fractures include sites such as tension-side femoral neck, patella, anterior tibia, medial malleolus, talus, tarsal navicular, proximal 5th metatarsal, and great toe sesamoids. These sites may require a period of non-weight bearing and may require surgical consultation given high risk of suboptimal healing given high tensile loads in areas of relatively poor vascularity (2,4).
- Patient’s symptoms should be monitored and patient should be kept pain-free during progression back to activity. Pain should not worsen during or after stopping exercise.
- If symptoms return, activity modification (reduction of load, volume, and/or intensity or use of non-impact mode) and further investigation for other etiologies may be needed.
- Education and risk factor modification/optimization are key in prevention.
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