Focal Spontaneous Osteonecrosis and Medial Meniscus Tear: Two Cases and a Literature Review

Abstract not available. Introduction provided instead.

Spontaneous or idiopathic osteonecrosis of the medial femoral condyle is a well-recognized cause of acute pain, tenderness over the joint line, effusion, and synovitis. Since the disease was first described by Ahlback and colleagues¹ in 1968, it has been the subject of several studies. Results from history, examination, and clinical studies suggest a complicated problem involving biomechanical and blood supply changes that tend to increase the susceptibility of the medial femoral condyle to avascular necrosis in the presence of meniscal pathology.^2-9 It remains unclear if the focal type of osteonecrosis arises from the insult of the arthroscopy or from an underappreciation of the disease in its early stages.

There are 2 types of avascular necrosis in the skeleton. The first, which occurs more commonly in patients aged 50 years or older, is focal spontaneous osteonecrosis (SO); the second, which tends to occur in patients aged 30 to 50, is
secondary osteonecrosis (2nd ON). The clinical presentations of these types of osteonecrosis must be distinguished when diagnosing and treating patients. SO is associated with tenderness over the joint line, unilateral knee involvement, and
acute pain exacerbated by increased weight-bearing.^4,8,10,11 With SO, most patients can remember the exact moment of symptom onset, and they describe pain increasing at night or at rest.^1,4,8,10-12 In contrast, 2nd ON generally shows bilateral involvement of multiple joints with gradual onset of diffuse pain.⁸ Secondary osteonecrosis is commonly associated with such predisposing factors as corticosteroid therapy, alcoholism, and systemic lupus erythematosus.^2,5,8,13-15

In patients with knee pain, early diagnosis requires a high index of suspicion for SO, as the diagnosis may not become apparent until months or years after symptom onset. Radiography, magnetic resonance imaging (MRI), and radionuclide bone scanning have proved capable of distinguishing SO from 2nd ON.8 MR and bone scan images are commonly used to identify the disease in its early stages,
and plain films are commonly used to rule out advanced disease when disease duration is not clear. Radionuclide techniques tend to confirm all 4 osteonecrosis stages.^8,10,11,16 Without early detection, SO treatment can become complicated
by the treatment required for the apparent overlying pathologies (eg, degenerative medial meniscal tears).

When patients aged 50 years or older present with acute onset of medially-based knee pain, the most common differential diagnosis includes SO, medial compartment osteoarthritis, and degenerative medial meniscus pathology. Here we describe 2 cases of SO diagnosed and treated initially as degenerative medial meniscus tears, and we illustrate the clinical diagnostic features of the disease.