Osteonecrosis

Osteonecrosis refers to necrosis of living bone tissue; traditional Chinese medicine calls it bone erosion. It can occur anywhere in the body. Causes are many, and clinically ischemic necrosis of the femoral head is most common; among ischemic bone necroses, femoral head necrosis has the highest incidence, determined by biomechanical and anatomical features.

Common Symptoms

Hip pain in the elderly; hip distension and discomfort

Causes

Etiology. Osteonecrosis is not a single disease but a common sign from multiple factors. Traumatic osteonecrosis is ischemic necrosis from destruction of major blood supply to part of bone; typical cases are subcapital femoral neck fracture or hip dislocation where the retinacular artery supplying the head is injured, causing femoral head necrosis; fractures and dislocations of the talus and lunate and scaphoid waist fracture can also cause ischemic necrosis by impairing blood supply. These are due to large-vessel supply disturbance, collectively called traumatic ischemic osteonecrosis. Pressure changes in the environment threaten health; divers and workers in high-pressure and high-altitude settings can develop osteonecrosis from vascular supply disturbance during rapid decompression, called decompression osteonecrosis. Many clinical cases show long-term supraphysiologic corticosteroids predispose to femoral head necrosis; radiation, alcoholism, pancreatitis, sickle cell anemia, Gaucher disease, liver disease, polycythemia, diabetes, obesity and hyperuricemia can also induce it. How these cause osteonecrosis is unclear, but most are thought hormone-related. Recent studies show multiple factors often coexist, suggesting multifactorial combined action. Pathogenesis. Normally bone is highly active, constantly forming and resorbing bone and remodeling to meet mechanical and biochemical needs; living bone responds to mechanical and chemical stimuli by changing formation or resorption rates. Bone repair is another complex process; regardless of the lethal cause, the repair response is basically the same, the only difference being that repair material for dead bone comes not from itself but from adjacent living bone, connective tissue and blood-borne osteoblasts. After necrosis, pathology has two stages. 1. Clearance stage: local necrotic bone and marrow cells, capillaries and matrix are gradually dissolved, transported and resorbed until dead bone disappears, though this is hard for large sequestra. 2. Repair stage: undifferentiated stromal cells and capillary endothelium near dead bone proliferate, infiltrating intertrabecular spaces and replacing necrotic marrow; stromal cells then differentiate into osteoblasts on necrotic trabeculae, forming new woven primitive bone and then lamellar bone wrapping the trabeculae, increasing local bone mass and appearing as increased density on X-ray; the wrapped necrotic trabeculae are gradually resorbed and replaced by living lamellar bone; finally repaired trabeculae are remodeled and woven bone is replaced by lamellar bone. This is not balanced: different sites repair at different rates, with the edge in remodeling while the center is still in early proliferation. Because resorption exceeds proliferation, the result is degenerative joint change with absorbed cartilage. Depending on cause, these reactions vary greatly: after renal transplant with heavy steroids, stroma proliferates but few cells become osteoblasts, so little new bone forms; in idiopathic osteonecrosis, abundant cells become osteoblasts and form much new bone. Traumatic ischemic necrosis repairs more completely, with rapid, extensive new bone once repair crosses the fracture line. Cortical repair is harder: much bone is resorbed with little new bone, causing large subchondral bone loss; if dead bone is not resorbed, mechanical strength holds for years, but once heavily resorbed, subchondral fracture occurs under stress, explaining the crescent-shaped radiolucent zone on X-ray.

Treatment

Supportive treatment, rehabilitation therapy

Prevention

Besides removing the cause, actively increase local blood supply, reduce loading and promote joint recovery. Traditional Chinese medicine considers osteonecrosis due to heat-toxin invasion, qi stagnation and blood stasis, rotten bone and marrow, and deficiency of essence and blood, treated by clearing heat, moving stagnation and tonifying the liver and kidney.

Recommended Department

It is recommended to visit the orthopedic surgery department; before the visit you may first book an appointment and connect with experts through this platform.

Warm reminder: The above information is provided for health education reference only and cannot replace professional medical diagnosis. If you have related symptoms, please seek care at a regular hospital in time.