KOHLER DISEASE (Articular osteochondrosis of the navicular bone).

A) ANATOMY:

The navicular bone is the last tarsal bone to ossify in the foot. This delayed development is thought to make the bone more susceptible to compression and subsequent vascular damage. If the damage is severe, then the blood supply to the navicular bone can be disrupted, producing avascular necrosis. 

A 3D representation of the blood supply to the navicular demonstrates vascular areas supplied laterally by the dorsalis pedis and medially by the posterior tibial artery. The central area (blue) is relatively avascular.

B) MRI IMAGING:

MRI typically shows decreased signal on T1-weighting and increased signal on T2-weighting in the early and mid stages of the disease. Osseous flattening may be present. Fragmentation of the navicular ossification center can occur, but the overlying cartilage is generally intact. Infection can mimic the clinical symptoms of Köhler Disease, and MRI can be useful in differentiating these entities, with features characteristic of osteomyelitis such as cortical erosion, adjacent soft tissue abscess, and overlying cellulitis (6a). Nuclear medicine scintigraphy can also be performed, typically showing decreased radiotracer uptake in the setting of Köhler Disease.

A sagittal fat-suppressed T2-weighted image centered at the midfoot demonstrates a decreased AP dimension and diffusely and heterogeneously increased signal intensity (arrow) throughout the navicular. Patchy areas of marrow hyperintensity within the hindfoot are likely related to altered biomechanics or disuse.

A sagittal fat suppressed T2-weighted image through the midfoot in a 5 year old girl complaining of pain along the medial side of the foot with limping, swelling, and bruising. The image demonstrates findings of osteomyelitis with severe marrow hyperintensity (arrow) within the ossified portion of the navicular and dorsal erosion of cortex. Soft tissue extension compatible with phlegmon and cellulitis is seen (arrowhead).

C) D.D.:
-To differentiate between avascular necrosis and osteomyelitis; look to the soft tissue near the affected bone if there is soft tissue edema or not.
-If the edema is present; the disease is osteomyelitis but if it is clear; it should be avascular necrosis.

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