• Hyo-Jin Byon, Jeong-Uk Han, Jong-Kwon Jung, Jeo-Woung Uhm, Junhyung Lee, and Hyunzu Kim.
• Department of Anesthesiology and Pain Medicine, Anesthesia and Pain Research Institute, Yonsei University College of Medicine, Seoul, South Korea.
• Pain Physician. 2022 Aug 1; 25 (5): E759-E765.

BackgroundThe effects of lumbar flexion on posterior longitudinal ligament (PLL) length as an acoustic window for neuraxial block in older patients have not been fully elucidated.ObjectiveThis study aimed to compare changes in PLL length during lumbar spine flexion in young and old patients.Study DesignObservational cohort study.SettingTertiary University Hospital.MethodsForty young and older adult patients were placed in the lateral decubitus position. To flex the lumbar spine, patients were asked to flex their hips and knees and then their neck and shoulder toward their knees as much as they could (fetal position). An assistant pushed the patients' abdomen to the back and held their neck and legs to help them maintain position. To obtain an optimal ultrasound view, lumbar spinal ultrasonography was performed from L5/S1 to L2/L3 using a paramedian oblique sagittal plane. PLL lengths were measured on the ultrasound image before fetal position, after unassisted fetal position, and after assisted fetal position.ResultsPLL lengths increased after lumbar spine flexion in both young and older adult  patients, except at the L3-L4 level in old patients. The change in PLL length during lumbar spine flexion was significantly lower in old patients than in young patients at the L5-S1 and L3-L4 levels (P = 0.0028 and P = 0.0134, respectively). After lumbar spine flexion, the PLL length was significantly different between the spinal levels in older patients (P = 0.0392).LimitationsFirst, we measured the PLL length as an acoustic window for neuraxial block using lumbar spinal ultrasonography. Second, the researcher who obtained the spinal ultrasound view was not blinded to the patient's group and position. However, the researcher who measured the PLL lengths on ultrasonography was blinded. Third, all participants had no history of surgery, trauma, or congenital abnormalities of the spine, regardless of age.ConclusionLumbar spine flexion can increase PLL length in young and old patients. However, lumbar spine flexion is less effective in increasing the PLL length in old patients than in young patients.

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