Kohler's bone disease is inflammation of the tarsal navicular bone (a bone at the arch of the foot).
Kohler's bone disease usually affects children aged 3 to 5 years (more commonly boys) and affects only one foot. The foot becomes swollen and painful, and the arch of the foot is tender. Weight bearing and walking increase discomfort, and the child's manner of walking (gait) is disturbed. X-ray studies show that the navicular bone is initially flattened and hardened and later breaks into fragments before healing and hardening back into bone. X-ray studies comparing the affected side with the unaffected side help assess how far the disease has progressed.
Kohler's bone disease rarely lasts beyond 2 years. Rest, pain relief, and avoiding excessive weight bearing are required. This disease usually resolves without treatment and without any long-term consequences. In severe cases, having the child wear a below-knee walking plaster cast (well molded under the length of the arch of the foot) for a few weeks may help.
Resource: Merck Manual Home Edition