Subchondral insufficiency fracture of the knee
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Spontaneous osteonecrosis of the knee, also known as Ahlback disease, SONK or evenSPONK has similar appearances to osteochondritis dissecans of the knee but is found in an older age group.
Epidemiology
SONK is seen more frequently in women (M:F 1:3), and affects older patients, typically over the age of 55.
Pathology
Osteonecrosis in SONK has no predisposing factors. However, by definition, secondary osteonecrosis of the knee occurs secondary to an insult. SONK is not thought to be caused by bone death but may be caused by osteoporosis and insufficiency fractures 6. Some authors suggest that the primary event leading to spontaneous osteonecrosis of the knee is a subchondral insufficiency fracture.
Radiographic features
It is almost always unilateral, usually affects the medial femoral condyle (but can occasionaloccasionally involve the tibial plateau9) and is often associated with a meniscal tear.
MRI knee
Features can vary dependant on the stage and include:
- ill-defined bone marrow oedema and a lack of peripheral low signal intensity rim as seen in avascular necrosis
(AVN)and bone infarcts - a focal subchondral area of low signal intensity adjacent to the subchondral bone plate and representing local ischaemia
(conisdered(considered is a specific MRI finding 12); this area shows no enhancement on post-contrast - deformity of the subchondral bone plate (flattening or focal depression) in the weight-bearing area of the involved condyle
Treatment and prognosis
Can varyPrognosis varies from complete recovery to total joint collapse 2. Treatment can either be operative or non operativenonoperative.
Differential diagnosis
History and etymology
It was first systematically described by Ahlback in 1968 2
-<p><strong>Spontaneous osteonecrosis of the knee</strong>, also known as <strong>Ahlback disease</strong>, <strong>SONK</strong> or even <strong>SPONK</strong> has similar appearances to <a href="/articles/osteochondritis-dissecans-of-the-knee">osteochondritis dissecans of the knee</a> but is found in an older age group.</p><h4>Epidemiology</h4><p>SONK is seen more frequently in women (M:F 1:3), and affects older patients, typically over the age of 55.</p><h4>Pathology</h4><p><a href="/articles/osteonecrosis">Osteonecrosis</a> in SONK has no predisposing factors. However, by definition, <a href="/articles/secondary-osteonecrosis-of-the-knee">secondary osteonecrosis of the knee</a> occurs secondary to an insult. SONK is not thought to be caused by bone death but may be caused by osteoporosis and insufficiency fractures 6. Some authors suggest that the primary event leading to spontaneous osteonecrosis of the knee is a subchondral insufficiency fracture.</p><h4>Radiographic features</h4><p>It is almost always unilateral, usually affects the medial femoral condyle (but can occasional involve the tibial plateau<sup>9</sup>) and is often associated with a <a href="/articles/meniscal-tear">meniscal tear</a>. </p><h5>MRI knee</h5><p>Features can vary dependant on the stage and include</p><ul>-<li>ill-defined bone marrow oedema and a lack of peripheral low signal intensity rim as seen in avascular necrosis (AVN) and bone infarcts</li>-<li>a focal subchondral area of low signal intensity adjacent to the subchondral bone plate and representing local ischaemia (conisdered is a specific MRI finding<sup> 12</sup>); this area shows no enhancement on post-contrast</li>- +<p><strong>Spontaneous osteonecrosis of the knee</strong>, also known as <strong>Ahlback disease</strong>, <strong>SONK</strong> or even <strong>SPONK</strong> has similar appearances to <a href="/articles/osteochondritis-dissecans-of-the-knee">osteochondritis dissecans of the knee</a> but is found in an older age group.</p><h4>Epidemiology</h4><p>SONK is seen more frequently in women (M:F 1:3), and affects older patients, typically over the age of 55.</p><h4>Pathology</h4><p><a href="/articles/osteonecrosis">Osteonecrosis</a> in SONK has no predisposing factors. However, by definition, <a href="/articles/secondary-osteonecrosis-of-the-knee">secondary osteonecrosis of the knee</a> occurs secondary to an insult. SONK is not thought to be caused by bone death but may be caused by osteoporosis and insufficiency fractures <sup>6</sup>. Some authors suggest that the primary event leading to spontaneous osteonecrosis of the knee is a subchondral insufficiency fracture.</p><h4>Radiographic features</h4><p>It is almost always unilateral, usually affects the medial femoral condyle (but can occasionally involve the tibial plateau <sup>9</sup>) and is often associated with a <a href="/articles/meniscal-tear">meniscal tear</a>. </p><h5>MRI</h5><p>Features can vary dependant on the stage:</p><ul>
- +<li>ill-defined <a href="/articles/bone-marrow-oedema">bone marrow oedema</a> and a lack of peripheral low signal intensity rim as seen in <a href="/articles/avascular-necrosis">avascular necrosis</a> and <a href="/articles/bone-infarction-1">bone infarcts</a>
- +</li>
- +<li>a focal subchondral area of low signal intensity adjacent to the subchondral bone plate and representing local ischaemia (considered is a specific MRI finding<sup> 12</sup>); this area shows no enhancement on post-contrast</li>
-</ul><h4>Treatment and prognosis</h4><p>Can vary from complete recovery to total joint collapse <sup>2</sup>. Treatment can either be operative or non operative.</p><h4>Differential diagnosis</h4><ul><li><a href="/articles/osteochondritis-dissecans-of-the-knee">osteochondritis dissecans of the knee</a></li></ul><h4>History and etymology</h4><p>It was first systematically described by <strong>Ahlback</strong> in 1968 <sup>2</sup></p>- +</ul><h4>Treatment and prognosis</h4><p>Prognosis varies from complete recovery to total joint collapse <sup>2</sup>. Treatment can either be operative or nonoperative.</p><h4>Differential diagnosis</h4><ul><li><a href="/articles/osteochondritis-dissecans-of-the-knee">osteochondritis dissecans of the knee</a></li></ul><h4>History and etymology</h4><p>It was first systematically described by <strong>Ahlback</strong> in 1968 <sup>2</sup></p>
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