Osteoporosis

Radiographic presentation and spinal changes

Global population aging is leading to a sharp increase in the number of osteoporotic fractures: projections show the number will reach 6.3 million per year by 2050. The axial skeleton is the most frequently affected site.

The pathophysiology of osteoporosis in the spine begins with the resorption of bone trabeculae. Horizontally oriented secondary trabeculae are destroyed first. To compensate for the loss of strength, the remaining vertical trabeculae thicken. On lateral spine radiographs and computed tomography, this creates a specific pattern — a vertical "striated appearance" (striated appearance).

An important aspect of differential diagnosis: in osteoporosis, this striating pattern is diffuse and involves the majority of vertebrae. If such a structure is visualized in only a single vertebral body, it is most likely a hemangioma.

Osteoporotic vertebral fractures

The anterior and central middle parts of the vertebrae biomechanically tolerate compression worse than the dense posterior elements. This determines the morphology of the fractures: they are more frequently wedge-shaped, affect the endplates, and are less commonly comminuted. Multiple wedge-shaped deformities in the thoracic spine form a pronounced kyphosis ("dowager's hump"), which in severe cases leads to impaired respiratory mechanics.

The semi-quantitative Genant classification is used to assess severity:

• Grade 1 (Mild): shape change (loss of height) of 20–25%.
• Grade 2 (Moderate): change of 26–40%.
• Grade 3 (Severe): change of more than 40%.

The presence of even a single vertebral fracture radically alters the prognosis: the risk of a subsequent hip fracture increases 2-fold, and a new vertebral fracture by 5-fold. For this reason, it is critically important for radiologists to use the term "fracture" (fracture) in their reports, avoiding soft wording such as "deformity" or "collapse", which leads to underdiagnosis.

Insufficiency fractures and atypical fractures

In addition to the spine, skeletal fragility leads to insufficiency fractures (insufficiency fractures) in specific load-bearing zones. Typical localizations: sacrum, pubic symphysis, pubic rami, and calcaneus. On scintigraphy, sacral involvement produces a characteristic H-shaped pattern (Honda sign). On radiographs, such fractures may be accompanied by marked osteolysis and mimic tumors. Magnetic resonance imaging has the highest sensitivity for detecting them.

Atypical femoral fractures (subtrochanteric and diaphyseal) are a serious complication of long-term bisphosphonate therapy. Radiologically, they are characterized by a transverse or short oblique fracture line and focal thickening of the lateral cortical layer with periosteal reaction. If cortical thickening is detected, the attending physician must be warned urgently, as this is a precursor to a complete fracture. Examination of both femurs is mandatory because the pathology is often bilateral.

Minimally invasive treatment: vertebroplasty and kyphoplasty

If an osteoporotic vertebral fracture causes persistent pain that is not relieved conservatively within 4–6 weeks, cement augmentation techniques are used. A mandatory prerequisite before intervention is a acute fracture with evidence of bone marrow edema on MRI (on fat-suppressed sequences).

1. Vertebroplasty: percutaneous transpedicular injection of polymethylmethacrylate (bone cement) directly into the cancellous bone of the fractured vertebra.
2. Balloon kyphoplasty: a special balloon is inflated within the vertebral body prior to cement injection. This creates a cavity, reduces injection pressure, and allows partial restoration of vertebral height.

Both methods effectively relieve pain, shorten hospital stays, and reduce mortality. Serious complications (such as spinal cord compression or pulmonary cement embolism) are rare, occurring in about 1%.

Regional forms of osteoporosis

Osteoporosis can be not only generalized but also localized (regional). The main forms include:

• Disuse osteoporosis (Disuse osteopenia): immobilization causes diffuse osteopenia, cortical resorption, and patchy radiolucencies in juxta-articular areas.
• Complex regional pain syndrome (reflex sympathetic dystrophy): sympathetic hyperactivity causes soft tissue edema, hyperemia, and excessive bone resorption, often in periarticular areas.
• Transient osteoporosis: sudden involvement of large joints (most commonly the hip) in young men or pregnant women in the third trimester. On MRI, the bone marrow edema pattern is detected long before radiographic changes.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Mechanisms of action of antiresorptive and anabolic pharmacotherapy for osteoporosis
• Honda sign and radiologic differential diagnosis of sacral fractures
• ASBMR morphological criteria for atypical femoral fractures
• Pathogenesis of transient osteoporosis of the hip and bone marrow edema
• Genant classification and semi-quantitative assessment in epidemiological studies

Other topics in the "Musculoskeletal System" section

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