Stress Fracture

Description

A stress fracture is a small, incomplete fracture or severe bone injury that occurs due to repetitive loading, overuse, or continuous stress on the bone. These fractures are commonly seen in athletes and military recruits who undergo intense physical training. Stress fractures most frequently occur in the weight-bearing bones of the lower extremities, such as the metatarsals, tibia, fibula, and femur. Unlike acute fractures that result from a single traumatic event, stress fractures develop over time from repeated mechanical loading.

Pathogenesis

Stress fractures result from the bone’s inability to withstand repetitive mechanical stress, leading to micro-damage that accumulates faster than it can be repaired. This repetitive stress can cause two main types of forces on the bone: compressive and tensile.

• Compressive Stress Fractures: These occur when the bone is subjected to repeated compressive forces, such as during running or jumping. The micro-damage accumulates on the concave side of the bone.
• Tensile Stress Fractures: These occur when the bone is subjected to repetitive tensile forces, such as pulling or bending. The micro-damage accumulates on the convex side of the bone.

Factors such as muscle fatigue, which reduces shock absorption, and biomechanical abnormalities can contribute to the development of stress fractures.

Subtypes

Stress fractures can be classified based on their location and underlying causes:

• Fatigue Fractures: Result from abnormal stresses on normal bone. Common in athletes and military personnel.
• Insufficiency Fractures: Result from normal stresses on weakened bone. Seen in conditions like osteoporosis, rheumatoid arthritis, and long-term corticosteroid use.

Epidemiology, Risk Factors & Associations

• Common in young athletes and older adults with osteoporosis.
• More common in females, particularly those with amenorrhoea or the female athlete triad (disordered eating, amenorrhoea, osteoporosis).

Greatest risk factors:

• Sudden increase in physical activity or intensity.
• Inadequate footwear.
• High-impact sports (e.g., running, gymnastics, basketball).

Most common associations:

• Osteoporosis increases the risk of insufficiency fractures.
• Female Athlete Triad disordered eating, amenorrhoea, and osteoporosis.
• Poor nutrition with deficiencies in calcium and vitamin D.
• Biochemical abnormalities such as hyperparathyroidism, low bone density.

Clinical Features

• Localised pain at the site of the fracture that worsens with activity and improves with rest.
• Mild swelling over the affected area.
• Point tenderness at the fracture site.
• Pain particularly in weight-bearing bones like the tibia and metatarsals.

Complications

• Complete Fracture: Stress fractures can progress to complete fractures if left untreated.
• Delayed Union or Nonunion: Inadequate healing due to continued stress or insufficient rest.
• Chronic Pain: Persistent pain if the fracture does not heal properly.
• Loss of Function: Decreased mobility or performance due to pain and weakness.

Pathological Features

Histopathology

• Macroscopic: Linear fracture or cortical disruption within the bone, without displacement.
• Microscopic: Microfractures, increased osteoclastic activity, and new bone formation.

Genetics

• Genetic predisposition to osteoporosis or metabolic bone diseases may increase the risk.

Radiological Features

General Features

• X-ray for initial assessment. MRI for detailed assessment and early detection (higher sensitivity).
• Initial X-rays may be normal. Later, periosteal reaction, cortical thickening, and fracture lines may become visible.

The tibia is the most common location for stress fractures, especially adolescent athletes, accounting for almost half of cases.

Common Locations1
Anterolateral Tibia	Typically subjected to tensile forces
Posteromedial Tibia	Typically subjected to compressive forces
Metatarsals	Particularly the second and third metatarsals, often subjected to compressive forces
Femoral Neck	High-risk area; tensile fractures occur on the superior side, and compressive fractures on the inferior side (more common paediatric, after skeletal maturity2).
Fibula	Commonly affected by compressive forces
Navicular	Central third is most commonly affected, often subjected to compressive forces

XR

• May be normal initially, later showing signs of stress fracture.
• Typical features of periosteal reaction, cortical thickening, visible fracture line.

CT

• Not typically used for diagnosing stress fractures.

MRI

• T1: Hypointense fracture line and bone marrow oedema.
• T2: Hyperintense bone marrow oedema, hypointense fracture line.
• STIR: Hyperintense bone marrow oedema (higher sensitivity).

US

• Not typically used for diagnosing stress fractures.

NM

• Bone Scintigraphy: Focal increased uptake at the fracture site due to bone remodelling.

Grading and Staging

Stress fractures are graded using MRI T2- (/STIR) and T1- weighted sequences to assess the severity and extent of bone injury³:

• Grade 1: Periosteal oedema on T2-weighted images. No marrow change.
• Grade 2: Periosteal oedema and bone marrow oedema on T2-weighted images.
• Grade 3: Periosteal oedema and bone marrow oedema on T1- and T2-weighted images.
• Grade 4: Fracture line visible on T1-weighted images, along with periosteal and bone marrow oedema on T1- and T2-weighted images.

Diagnosis

• Clinical examination and history, particularly noting the onset of localised pain and recent changes in activity levels.
• Imaging studies (X-ray, MRI, bone scintigraphy) showing characteristic features of stress fractures.
• Laboratory tests: May include bone turnover markers and metabolic bone panel if underlying metabolic bone disease is suspected.

Differential Diagnosis

Image-based

• Tendinitis: Inflammation of the tendons. Pain with tendon palpation, swelling. Tendon thickening with increased signal on T2.
• Osteomyelitis: Infection of the bone. Fever, localised pain, elevated inflammatory markers. Bone destruction, periosteal reaction, abscess.
• Bone Tumours: Benign or malignant bone lesions. Persistent pain, possible swelling, palpable mass. Bone lesions, cortical destruction, periosteal reaction.

Clinically-based

• Shin Splints (Medial Tibial Stress Syndrome): Overuse injury causing pain along the tibia. Diffuse pain along the shin, worse with activity. May show periosteal reaction without discrete fracture line. On MRI the area of high signal intensity often is more linear (rather than diffuse/irregular) and is limited to the medial aspect of the tibia
• Compartment Syndrome: Increased pressure within a muscle compartment. Severe pain, swelling, numbness, decreased pulses. MRI may show muscle oedema.
• Plantar Fasciitis: Inflammation of the plantar fascia. Heel pain, worse with the first steps in the morning. Ultrasound may show thickened plantar fascia.

Management

• Requires orthopaedics or sports medicine input for specialised care.
• Non-surgical management:
  • Rest and Activity Modification: Cease activities that exacerbate symptoms and introduce low-impact activities.
  • Immobilisation: Use of braces or walking boots to offload the affected area.
    • Compressive Fractures: Immobilisation and reduced weight-bearing to decrease compressive forces.
    • Tensile Fractures: Offloading and potentially using crutches to avoid tensile stress.
  • Physical Therapy: Strengthening and flexibility exercises to support the affected area and prevent recurrence.
  • Nutrition: Ensure adequate intake of calcium and vitamin D.
  • Medications: Analgesics for pain control.
• Surgical management:
  • Reserved for fractures that fail to heal with conservative treatment or in high-risk areas like the femoral neck.
  • Procedures may include internal fixation to stabilise the fracture.
• Other treatments:
  • Addressing underlying risk factors such as correcting biomechanical abnormalities, ensuring proper footwear, and managing osteoporosis.
  • Regular follow-up with imaging to monitor healing progress.

References

1. Liong, S.Y., & Whitehouse, R.W. (2012). Lower extremity and pelvic stress fractures in athletes. British Journal of Radiology, 85(1016), 1148-1156 ↩︎
2. Jaimes, C., Jimenez, M., Shabshin, N., Laor, T. and Jaramillo, D., 2012. Taking the stress out of evaluating stress injuries in children. Radiographics, 32(2), pp.537-555. Vancouver ↩︎
3. Fredericson, M., Bergman, A.G., Hoffman, K.L. and Dillingham, M.S., 1995. Tibial stress reaction in runners: correlation of clinical symptoms and scintigraphy with a new magnetic resonance imaging grading system. The American journal of sports medicine, 23(4), pp.472-481. ↩︎