Curves of the achondroplastic spine: a new hypothesis.

The profile of the achondroplastic dwarf reflects abnormalities in the shape of the spine, particularly in the lumbosacral area. We hypothesize that these abnormalities and the resultant symptoms are secondary and avoidable rather than heritable and inevitable. Because the heads of achondroplastic children are enlarged (n = 50), loading of the vertical spine is increased. Unusually lax ligaments and misshapen vertebrae predispose the spine to yielding under vertical stress. Children and adults uniformly have hip flexion contractures (n 105); these are hypothesized to be the result of uncorrected lumbosacral lordosis. The volume of the spinal canal, reduced by the spinal stenosis of achondroplasia, is decreased additionally by lordosis; some neurologic deficits of achondroplasia are caused by this abnormal curvature. This hypothesis bears practically on treating this common form of dwarfism.