Stress fractures

Stress fractures refer to fractures occurring in bone due to a mismatch of bone strength and chronic mechanical stress placed upon the bone. Fractures can either be:

Radiographs have limited sensitivity for an acute stress fracture, although repeat delayed radiograph may show changes of healing. MRI is the most sensitive modality for diagnosis of stress fracture and is important tool to distinguish high and low risk fractures to help clinicians for management plans 5,6.

A pathological fracture, although a type of insufficiency fracture, is a term in general reserved to fractures occurring at the site of a focal bony abnormality. Some authors use the term stress fracture synonymously with fatigue fracture, and thus some caution with the term is suggested.

Stress fractures normally present with worsening pain with a history of minimal or no trauma. In the lower (weight bearing) limb, there is often a history of a recent increase of physical activity or significant alteration in the type or duration of normal athletic activity.

Stress fractures are far more common in the lower limb (~95%) than the upper limb 5. High-risk sites of stress fractures are locations at greatest risk of fracture propagation, displacement or non-union. These sites are under tensile stresses and have poor vascularity. These include:

  • superior side of the femoral neck
  • anterior tibial cortex
  • 5th metatarsal base
  • great toe sesamoids (hallux sesamoids)
  • talar neck
  • posterior cortex of tarsal navicular
  • 2nd to 4th metatarsal necks
  • medial malleolus
  • femoral head
  • patella
  • pars interarticularis of the lumbar spine

Low-risk sites of stress fracture are at low risk of complications and are under compressive stresses. They include:

  • calcaneus
  • pubic rami
  • sacrum
  • ribs
  • proximal humerus/humeral shaft
  • posterior medial tibial shaft
  • 2nd to 4th metatarsal shafts

Plain radiographs have poor sensitivity (15-35%) in early-stage injuries, which increases in late-stage injuries (30-70%). MRI is the modality of choice with a sensitivity reported to reach close to 100% 6.

Plain radiographs have poor sensitivity in detecting stress fractures, as positive findings may take months to appear. During the first few weeks after the onset of symptoms, x-rays of the affected area may look normal.

Positive findings can include:

  • grey cortex sign: subtle loss of cortical density in early-stage stress injury
  • increasing sclerosis or cortical thickening along fracture site
  • periosteal reaction/elevation
    • may take up to 2 weeks to be detectable
  • fracture line

Bone scans can show evidence of stress fracture within a few days upon the onset of symptoms. As a modality, it is considered less sensitive than MRI 5.

Stress fractures on bone scintigraphy appear as foci of increased radioisotope activity ('hot spot') due to increased bone turnover at the site of new bone formation. However, as with all bone scintigraphy, this is non-specific; the increased uptake can also be due to osteomyelitis, bone tumors or avascular necrosis.

The findings are similar to plain radiography, including sclerosis, new bone formation, periosteal reaction, and fracture lines in long bones.

CT may be useful in differentiating stress fractures from bone tumor or osteomyelitis if the plain radiographs are negative and bone scans are positive.

MRI is the most sensitive modality for detecting stress fracture, and may also be useful for differentiating ligamentous/cartilaginous injury from bone injury.

Typical MRI appearance of stress fracture includes:

  • periosteal or adjacent soft tissue edema
  • band-like bone marrow edema
  • T1 hypointense fracture line evident in high-grade injury

Treatment is determined by the site of the stress fracture and suitability for rehabilitation.

Fractures at low-risk sites are managed conservatively with analgesia, ice, reduced weight bearing and modification of activities until pain resolves.

At high-risk sites or in patients where long-term rehabilitation is detrimental to their livelihood (i.e. athletes or labourers), orthopedic consultation is required.

Risk factors such as diet, vitamin D and calcium should be addressed to prevent recurrence. Other factors such as a gradual return to training and biomechanical evaluation of gait may be required. Bone density evaluation can be considered in patients with recurrent stress fractures, family history of osteoporosis or in stress fractures unexplained by exercise activity.

  • osteosarcoma and bone tumors can also present with periosteal reaction
  • osteomyelitis has marrow edema and soft tissue swelling
  • soft tissue bruise: has edema at the injury site, but little marrow abnormality
  • in addition to the risk stratification by location, any displacement or proximal femur fractures with a fracture line >50% the width of the femoral neck should also be considered high-risk 6
Fractures
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rID: 7542
Synonyms or Alternate Spellings:
  • Stress fracture

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  • Case 8: involving left femoral neck in a child
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  • Case 9: involving distal tibia on MRI
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  • Case 16: bone scan static images
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  • Case 17: of the second metatarsal
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  • Case 18: femoral neck stress fracture
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  • Case 20: pubic ramus stress fracture
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  • Case 21: second metatarsal
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  • Case 22: second metatarsal
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