Pathogenesis and classification
Normally, the bone remodeling cycle maintains bone strength: osteoclasts remove microdamage, and osteoblasts synthesize new matrix. However, when the frequency of subcritical loading cycles is excessively high (e.g., during a sudden increase in running distance), the remodeling process cannot keep up with the destruction.
The process goes through two stages:
- Stress reaction (Stress reaction). The macroscopic contour of the bone is preserved, and damage accumulates only at the microscopic level.
- Stress fracture. The bone architecture fails, and the bone breaks into fragments (similar to a metal paperclip repeatedly bent).
Globally, there are two mechanisms of development:
- Fatigue fracture (Fatigue fracture): occurs in completely healthy bone due to an excessive number of loading cycles.
- Insufficiency fracture (Insufficiency fracture): develops under normal, everyday loads, but in pathologically altered bone (against the background of osteoporosis, osteomalacia, or Paget's disease).
Biomechanics and typical localizations
Stress fractures occur in zones of maximum cyclical loading. Pressure distribution depends on foot anatomy and gait patterns:
- Flatfoot (Flatfeet). Leads to excessive bending of the second and third metatarsal necks. In recruits after long forced marches with heavy backpacks, the so-called «march fracture» frequently occurs here.
- High arched foot (High arched foot). Characterized by increased rigidity and shifts weight bearing to the outer edge. This overloads the navicular bone and the base of the fifth metatarsal bone, provoking a Jones fracture (Jones fracture).
- Calcaneus (tuber calcanei). Affected in runners from constant heel striking against the surface.
- Sesamoid bones (ossa sesamoidea). Damaged beneath the first metatarsophalangeal joint during forceful push-off (sprinting, jumping).
Clinical presentation and diagnostics
The main symptom is local aching pain that worsens with physical activity and subsides at rest. Patients often report a recent sharp increase in training loads.
To differentiate a calcaneal fracture from plantar fasciitis, the calcaneal squeeze test (calcaneal squeeze test) is used: compressing the calcaneal tuberosity from the sides causes sharp pain.
Instrumental diagnostics:
- Radiography. Low diagnostic value in early stages. Changes are visible only when a distinct fissure or bone callus forms (weeks later).
- MRI. The gold standard for early diagnosis. Visualizes bone marrow edema, allows monitoring of healing, and helps rule out the diagnosis if findings are normal.
- Bone scintigraphy. A sensitive but outdated method, inferior to MRI in accessibility.
Treatment: conservative and surgical
Since this is an overuse injury, the cornerstone of conservative treatment is rest. Patients are prescribed decreased axial loading, crutches, a CAM walker boot, and rigid-soled shoes.
Surgical treatment is used in cases of high risk of nonunion, fragment displacement, or recurrence. «High-risk» fractures include:
- Jones fracture. Requires screw stabilization through the medullary canal and reaming to stimulate blood flow.
- Navicular fractures. Due to poor blood supply, they heal poorly. They frequently require screw fixation, bone grafting, and prolonged weight-bearing restriction.
- Sesamoid fractures. Surgery (osteosynthesis or bone excision) is considered a treatment of last resort if specialized custom orthoses with recesses fail to help.
Briefly: answers to topical questions
What pathological conditions are included in the female athlete triad syndrome?
The female athlete triad syndrome includes three interrelated clinical conditions representing a spectrum of disorders.
- Disordered eating (disordered eating) — energy or nutritional deficiency that can lead to a critical decrease in body fat mass.
- Amenorrhea (amenorrhea) — menstrual cycle disorders up to complete absence of menstruation against the background of lowered estrogen levels.
- Osteoporosis (osteoporosis) — a decrease in bone mineral density due to excessive bone resorption.
What stages of bone callus formation does a stress fracture go through during consolidation?
During fracture consolidation, bone callus formation goes through three main clinical stages.
- Stage of primary union — characterized by the formation and differentiation of mesenchymal tissue, hematoma resorption, and reduction of traumatic inflammation.
- Stage of soft callus — distinguished by the formation of a bendable callus, during which bone fragments become less mobile.
- Stage of bony union — represents the phase of calcification of the osteoid callus, accompanied by complete disappearance of fragment mobility under axial loading.
To memorize the female athlete triad (highest risk group), use the AED rule: Amenorrhea, Eating disorders, Decreased bone mineral density (Osteoporosis). Fat tissue deficiency leads to estrogen deficiency, which disrupts bone remodeling.
Class and exam questions
Why might an X-ray show nothing upon the first complaint of pain?
Radiography displays already formed structural destruction or bone callus. In the initial stage of a stress reaction, when only microscopic bone defects are present, the pathology can only be seen on MRI.
How does a Jones fracture differ from an avulsion fracture of the fifth toe?
A Jones fracture is localized at the metaphyseal-diaphyseal junction of the fifth metatarsal bone (in the transition zone from flexible to rigid bone), whereas an avulsion fracture is located at the very tip of its base.
How to distinguish a sesamoid stress fracture from an anatomical variant?
A bipartite sesamoid is frequently mistaken for a fracture. In this developmental anomaly, the fragments have smooth edges and are present on both feet, whereas in a traumatic fracture, the bone edges are jagged and uneven.
What else to study on this topic
- The influence of foot arch biomechanics on the distribution of cyclical loading.
- Differential diagnosis of stress fractures and foot tendinitis.
- Pathophysiology of bone remodeling (the role of osteoclasts and osteoblasts).
- Hormonal and dietary risk factors: the impact of calcium, vitamin D, and estrogen.
- Surgical techniques and the use of bone grafts in navicular fractures.
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