Lumbar nerve root occupancy in the foramen in achondroplasia: a morphometric analysis.
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.


METHODS
Level I, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.
Modi
Hitesh N
HN
Department of Orthopedics, Korea University Guro Hospital, # 80, Guro-Dong, Guro-Gu, Seoul, 152-703, Korea.
Suh
Seung Woo
SW
Song
Hae-Ryong
HR
Yang
Jae Hyuk
JH
D000130:Achondroplasia / Q000150:complications / Q000473:pathology*; D000293:Adolescent; D000328:Adult; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007403:Intervertebral Disc / Q000473:pathology*; D017116:Low Back Pain / Q000473:pathology; D008159:Lumbar Vertebrae; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009408:Nerve Compression Syndromes / Q000150:complications* / Q000209:etiology / Q000473:pathology; D011446:Prospective Studies; D013115:Spinal Canal / Q000473:pathology*; D013126:Spinal Nerve Roots / Q000473:pathology*; D013128:Spinal Osteophytosis / Q000150:complications* / Q000209:etiology / Q000473:pathology; D013130:Spinal Stenosis / Q000209:etiology* / Q000473:pathology