1. In the lumbar spinal canal of the achondroplast there is decreased cross-sectional area. In addition the intervertebral foramina are narrow. These changes result in reduced area for the dural sac and exiting spinal nerves. 2. There is associated thoracolumbar kyphosis and a lumbosacral hyperlordosis. These sagittal plane changes result in increased tension on the dural sac and nerves. 3. With aging there is disc degeneration with disc space narrowing and osteophyte formation. In addition facet hypertrophy with osteophyte formation are common. These degenerative changes further reduce the size of an already compromised spinal canal and intervertebral foramina. The above understanding of the normal spinal and anatomy in the achondroplast, and the added effects of aging allow the surgeon to plan a logical treatment regimen for neurological problems in the achondroplast. Fig. 6. Cross-section at the di sc level of an achondroplast (A) and an age matched non-achondroplast (B). The cross-sectional area of the spinal canal is reduced in the achondroplast, with a reduction in the antero- posterior canal (C vs. C 1 ).
There is facet hyper- trophy extending into the nerve root canal and into the spinal canal lateral recess (B vs. B 1 ). In ad- dition the nerve root canal is markedly reduced in-the achondroplast (D vs. D1 ). (Reprinted with permis- sion, as of Fig. 5). 225 REFERENCES 1. R. J. Eulert, Scoliosis and kyphosis in dwarfing conditions, Arch. Orthop.Traum. Surg.102:45 (1983).