Lumbosacral transitional segments: classification, prevalence, and effect on disk height.

Objective: To determine the rate of lumbosacral transitional segments among chiropractic practice settings and to determine if this anomaly would affect the height of the lumbosacral disk.

Study Design: Retrospective review of radiographs.

Setting: Los Angeles College of Chiropractic outpatient clinic and a private chiropractic office.

Samples: A total of 20 lumbar series with lumbosacral transitional segments from a private chiropractic office, 47 lumbar series with lumbosacral transitional segments, and 60 age- and sex-matched control series from a college clinic.

Results: A total of 2.3% of 882 lumbar series at the private chiropractic office and 6.5% of 786 lumbar series at the Whittier Health Center showed lumbosacral transitional segments of types II, III, or IV. The L5-S1 intervertebral disk height was significantly smaller in patients with lumbosacral transitional segments compared with those without (ie, 11% vs 19% of total lumbar disk height, respectively). When bilateral bony fusion of L5 to the sacrum was present, the L5-S1 disk height was significantly smaller than that without bony fusion (ie, 8% vs. 12% to 14% of total lumbar disk height, respectively).

Conclusions: We conclude that the rate of occurrence of lumbosacral transitional segments is low in chiropractic practice. In the presence of lumbosacral transitional segments, especially when there was bony fusion, the lumbosacral intervertebral disk was significantly narrower than the upper lumbar disks, which should not be considered as disk degeneration or displacement. The type of lumbosacral transitional segment present also showed a significant effect on the height of the lumbosacral disk.