Perthes' disease and posterior lumbosacral union.

Delayed bone development is common in Perthes' disease, and affected children are usually smaller than normal. Somatosensory evoked potentials (SEP) studied in 25 cases of Perthes' disease were normal. Fifty-four patients with active or healed Perthes' disease were examined. Every child aged less than 8 years showed failure of posterior lumbar and/or sacral fusion. With growth, fusion increased so that at age 14 years 50% had a normal fusion and 50% had spina bifida occulta. At age greater than 16 years, the incidence was similar to that in the general population. In Perthes' disease, growth in fusion of the lumbosacral elements is delayed.