Background: Data on the L3/4 and L4/5 interspinous distances are important in performing a lumbar puncture. This has not been studied in Thais.
Objective: To study the interlaminar and the narrowest distances at the L3/4 and L4/5 interspinous spaces and location of the intercrestal line in Thai cadavers.
Material and Method: The interlaminar and the narrowest distances at the L3/4 and L4/5 interspinous spaces and location of the intercrestal line were measured in 87 cadavers. Mean age of cadavers was 66.7+10.6 years (range 40-80 years). Measurements were statistically analyzed using unpaired t-tests.
Results: The intercrestal line most often intersected at the lower half of the L4 spinous process (32/87, 36.8%), ranging from the lower half of L3 spinous process to the upper half of S1. Mean interlaminar and the narrowest distances at the L3/4 interspinous space were not significantly different from the L4/5 interspinous space: 7.32+2.7 mm vs. 7.05+3.0 mm and 5.27+2.1 mm vs. 5.38+2.4 mm, respectively (p>0.05). These interspinous process distances in 71-80 year old cadavers were significantly shorter than 40-60 and 61-70 year age groups (p<0.05).
Conclusion: The present study confirms that the intercrestal line is most commonly at the lower half of the L4 spinous process. Mean interlaminar and the narrowest distances at the L3/4 and L4/5 interspinous spaces were unrelated to gender or body type. The elderly had more narrow interspinous process distances which may be benefit from having lumbar puncture done in the sitting and feet supported position.

Keywords: Lumbar puncture, Lumbar vertebra, Lumbar spine, Intercrestal line, Interspinous space