OBJECTIVE. To test the hipothesis of an anatomic and functional reserve in the spinal canal that explains the radiological changes in lumbar spine of asymptomatic individuals, the differences in modalities of clinical presentation and the discrepancies in the prevalence of mechanical and degenerative low back pain and sciaticas. CASES AND METHODS.. Two groups of 27 persons were submitted to computed axial tomography. In one group, the patients presented low back pain and/or sciaticas. The other formed by matched controlls, showed no signs or symptoms. The bony canal area, dural sac area, interfacets distance and lateral recesses depth were quantitative assessed. RESULTS. The asymptomatics ones had larger bony canals than the acute and chronic patients, due to statistical significant differences. The ranges responsible for these differences and whose averages had higher figures in the asymptomatics ones in relation to the chronic patients, were the bony canal areas at L3-L4, L4-L5, the dural sac area and lateral recesses depth at L4-L5; in relation to acute ones: the bony canal areas at L3-L4, L4-L5, L5-S1, dural sac area at L4-L5, L5-S1, and sagittal diameter L5-S1 and lateral recesses depth at L4-L5. CONCLUSIONS. The radiological changes in asymptomatic ones, the lack of symptoms in the control group, the presence of chronic and acute features and the discrepancies in the prevalence of low back pain were attributed to the existence of an anatomic and functional reserve. This reserve would be determined by the presence of a "safety factor" which would have differential distribution in asymptomatics, acute and chronic. It would be the element able to influence the presence or absence of low back pain in persons with radiological changes
Anatomic and functional reserve; Mechanical low back pain; Sciaticas; Spinal canal; Radiological changes in asymptomatic persons
