Other Avascular Necrosis Syndromes

KOHLER DISEASE OF THE TARSAL NAVICULAR This is an uncommon condition affecting boys more commonly than girls (4:1), occurring at about 5 years of age in boys and at about 4 years of age in girls. It appears to result from repetitive compressive forces applied to the tarsal navicular, the last bone of the foot to ossify in normal children. Affected children appear to have a delayed ossification of this bone during a critical phase in its growth, predisposing it to the compressive stresses of preschool ambulation.

The child presents with an antalgic limp, bearing weight on the lateral side of the foot, thus splinting the medial longitudinal arch. The child complains of local pain and tenderness over the navicular bone of the foot and often has induration over the area. There is no fever or other constitutional symptoms. Range of motion of the other joints of the foot is intact.

Radiographically, the picture is classic. The tarsal navicular is narrowed, as seen in the lateral view of the foot and ankle, and flattened, with irregular rarefaction and sclerosis. Comparison of radiographs of the contralateral foot is often helpful.

Treatment is as an outpatient using a short-leg walking cast. The use of crutches to ensure non-weight bearing is recommended for the initial 3 weeks. Orthopedic aftercare should be arranged. The prognosis is very good.

FRIEBERG INFARCTION This condition of adolescents is seen much more commonly in girls (3:1). The usual site of involvement is the head of the second metatarsal, although other metatarsals can be affected, and it is occasionally bilateral. While its etiology is not known with certainty, it is generally presumed to be caused by a vascular insufficiency (aseptic necrosis).

Clinically, the patient complains of pain and tenderness under the affected metatarsal head. This is associated with local soft tissue swelling and restricted range of motion of the metatarsophalangeal joint. Radiographs of the foot demonstrate flattening, sclerosis, and irregularity of the metatarsal head. CT scan or technetium-99m bone scan may serve to clarify the diagnosis in selected patients whose diagnosis remains obscure.

Management is as an outpatient, utilizing a short-leg walking cast for 3 to 4 weeks. Follow-up care is provided by an orthopedist who may recommend a surgical excision of the affected area of metatarsal if conservative therapy is ineffective.

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