Lumbar stenosis is common in patients with achondroplasia because of narrowing of the neural canal. However, it is unclear
what causes stenosis, narrowing of the central canal or foramina. We performed a morphometric analysis of the lumbar nerve
roots and intervertebral foramen in 17 patients (170 nerve roots and foramina) with achondroplasia (eight symptomatic, nine
asymptomatic) and compared the data with that from 20 (200 nerve roots and foramina) asymptomatic patients without achondroplasia
presenting with low back pain without neurologic symptoms. The measurements were made on left and right parasagittal MRI scans
of the lumbar spine. The foramen area and root area were reduced at all levels from L1 to L5 between the patients with achondroplasia
(Groups I and II) and the nonachondroplasia group (Group III). The percentage of nerve root occupancy in the foramen between
Group I and Group II as compared with the patients without achondroplasia was similar or lower. This implied the lumbar nerve
root size in patients with achondroplasia was smaller than that of the normal population and thus there is no effective nerve
root compression. Symptoms of lumbar stenosis in achondroplasia may be arising from the central canal secondary to degenerative
disc disease rather than a true foraminal stenosis.
Level of Evidence: Level I, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.
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