Spontaneous Osteonecrosis of the Knee

Excerpt

Spontaneous osteonecrosis of the knee is a debilitating condition characterized by the sudden onset of knee pain and functional impairment, primarily affecting the medial subchondral bone of the femoral condyles (see Image. Osteonecrosis of the Knee). Ahlbäck first described the condition in 1968, highlighting its hallmark features of a nontraumatic origin and rapid progression. Unlike secondary or post-arthroscopic osteonecrosis, no definitive consensus exists concerning the condition's etiology. However, if left untreated, it can progress to subchondral collapse and secondary osteoarthritis, thereby necessitating surgical intervention.

Given the nonspecific and insidious onset, diagnosing and treating spontaneous osteonecrosis of the knee can be challenging. Understanding the anatomy of the knee joint is crucial, as the disease mainly impacts the medial femoral condyle, which bears significant weight-bearing stress and may contribute to its development. In contrast, the involvement of the lateral femoral condyle and the tibial plateau is less common.

The natural history of spontaneous osteonecrosis of the knee typically follows a pattern of sudden symptom onset without a preceding injury, followed by rapid joint deterioration. Distinctive crescent-shaped osteonecrosis lesions also characterize this condition, and the progression is influenced by various factors, including the size and location of the lesion and the patient's overall health status. The speed and pattern of spread vary, with some patients experiencing a slow progression while others face rapid joint destruction. Some instances of spontaneous osteonecrosis of the knee are self-limiting, with symptoms resolving spontaneously over time. However, in many patients, the disease progresses, often resulting in sudden, intense knee pain, swelling, functional impairment, and the risk of joint deterioration. Early stages are marked by severe pain and swelling, progressing to joint space narrowing and osteoarthritic changes. In advanced cases, the necrotic bone may collapse, leading to severe osteoarthritis requiring joint replacement surgery.