Morphometric analysis of 900 lumbar intervertebral discs: Anterior and posterior height analysis and their ratio

Objective: To evaluate the height of normal intervertebral discs and describe their differences after analyzing anterior and posterior height.Methods: Retrospective study based on analysis of analysis of lumbar spine magnetic resonance imaging. We included male and female patients who underwent lumbar spine resonance, most of them for investigation of low back pain. Patients with previous surgeries, advanced degenerative disc disease, suspected infection, deformities were excluded from the study.Results: 300 patients had their images analyzed for the anterior and posterior height of the L3-L4, L4-L5 and L5-S1 discs, totaling 900 intervertebral discs. The mean age of the patients was 46,2 +/- 15,1 years. The mean anterior disc height of L3-L4 was 9.30 mm, L4-L5 10.94 mm and L5-S1 12.41 mm. About 7% of the patients have a L3-L4 anterior height < 7 mm, which is usually the smallest available cage height. The ratio obtained by dividing the anterior height by the posterior height was 1,47 for L3-L4; 1,62 for L4-L5 and 2,00 for L5-S1. It means that the posterior disc height is half the anterior disc height for the L5-S1, making this segment the most important in the formation of lumbar lordosis. The anterior disc height showed progressive decrease with aging, with Pearson correlation value of -0,36 for L3-L4, -0,96 (p < 0,05) for L4-L5. The L5-S1 anterior disc height has not change with aging r=0,005 (p > 0,05).Conclusions: L3 to L5 discs present greater anterior height than posterior and this difference tends to decrease with aging. The L5-S1 disc is that most contributes for lumbar lordosis, followed by L4-L5. Populations with lower average height should have their disc dimensions carefully studied during surgical planning, especially in L3-L4 segment.