Atraumatic Osteonecrosis of the Knee
ABSTRACT & COMMENTARY
Synopsis: This large series with long-term follow-up documented the effectiveness of magnetic resonance imaging as a screening tool and prognosticator for atraumatic osteonecrosis of the knee, and the efficacy of core decompression as a treatment modality.
Source: Mont MA, et al. Atraumatic osteonecrosis of the knee. J Bone Joint Surg Am 2000;82:1279-1290.
Atraumatic osteonecrosis of the knee is a disorder affecting younger patients who generally have comorbidities. This is in contrast to spontaneous osteonecrosis of the knee that generally affects older patients, especially females, often in their 60s and 70s. The latter is more focal and limited in extent to the subchondral region of usually just one femoral condyle. Atraumatic osteonecrosis, on the other hand, is more diffuse, frequently involving both femoral condyles as well as the tibia, and often presenting with multiple joint involvement and bilaterality. Atraumatic osteonecrosis of the knee has a strong correlation with autoimmune diseases and steroid use. However, the literature is lacking in good, long-term studies that help with prognosis and treatment alternatives.
Mont and associates provide a review of their experience with 248 knees in 136 patients who were treated over a 24-year period at Johns Hopkins. The patient population was limited to those younger than 55 years of age to avoid overlap with the spontaneous osteonecrosis population. Seventy-four percent had a comorbid disease that affected the immune system, most commonly Lupus. Ninety percent had a history of corticosteroid use. Diagnostically, bone scan missed lesions 30% of the time, leading Mont et al to recommend MRI as the screening modality of choice for the involved joint and any other symptomatic joint.
Initially, treatment involved three months of conservative measures including protected weight-bearing and anti-inflammatory medication. Those patients who failed to improve underwent core decompression with a 79% clinical success rate. This was sustained to a mean of seven years. For those with recurrent symptoms, repeat core decompression was effective in 60%. Arthroscopic debridement was combined with repeat core decompression if patients developed more localized joint line tenderness or mechanical symptoms. Only 20% of the patients treated nonoperatively had clinical success. Furthermore, knee replacements faired terribly in this population with only 71% success at nine years, and an unacceptably high rate of loosening. This poor outcome was the same whether the patients were treated first with core decompression prior to replacement.
Prognostically, Mont et al found that size of the lesion and location in the epiphysis—as opposed to the metaphysis—was the most prognostic for poor outcome. Lesions larger than 250° (the combined necrotic angle on the AP and lateral view of the magnetic resonance imaging [MRI]) had a worse prognosis. Based on the positive response to core decompression and the very poor response to nonoperative treatment, Mont et al now recommend immediate core decompression upon patient presentation rather than waiting for three months of nonoperative treatment.
Comment by David R. Diduch, MS, MD
This is an exceedingly well-written paper with a large number of patients with sufficient long-term follow-up. This will soon be referenced widely because it gives us excellent data on which to base treatment recommendations. Although the sports medicine physician may not think of atraumatic osteonecrosis as a common problem in their patient population, we frequently are the ones ordering a MRI and determining the course of treatment, and we frequently are involved in joint restorative procedures about the knee. This article clearly points out the difference between atraumatic osteonecrosis and spontaneous osteonecrosis. They clearly define the epiphyseal location and large lesions as high risk factors for poor outcome. They also present an excellent case for core decompression to alter the natural history in positive fashion. It is important to note that this was maintained over the long term. Their core decompression technique involves radiographic-guided decompression from an extra-articular starting location. The ACL tibial guide and cannulated reamers can be helpful in this regard.
There are many take-home lessons in this paper. Upon presentation, we should have a high suspicion for other joint involvement and use MRI as a screening tool liberally. This is because core decompression appears to offer the ability to alter the natural history of this problem. It would also appear that nonoperative treatment of symptomatic lesions has a poor prognosis. It would also appear that repeat core decompression with arthroscopic debridement can be successful even if the initial treatment did not relieve symptoms. Finally, we are to be cautioned regarding recommending knee replacement in this patient population. They have a very high rate of both aseptic and septic loosening. This is due to their frequent autoimmune disease comorbidity, poor bone stock, and associated corticosteroid use. Cemented knee replacements with long stems are probably ideal.
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