Osteonecrosis of the knee involves the death of bone tissue, typically in the femoral condyle, due to insufficient blood supply. It may be idiopathic (no known cause) or secondary to trauma, prolonged corticosteroid use, alcohol abuse, or systemic diseases.

Patients often report localized pain, typically on the inner side of the knee, worsened by weight-bearing and sometimes present at rest. Joint stiffness and restricted movement are also common, even without a recent injury.

Diagnosis relies on clinical evaluation and imaging. X-rays may appear normal in early stages, while MRI is more sensitive in detecting early necrotic changes. Treatment depends on the severity: conservative approaches are used initially, while advanced stages may require surgical intervention.

If left untreated, the necrosis can progress, resulting in bone collapse, joint deformity, and secondary osteoarthritis, with increasing functional impairment.