Hip flexion and lumbar puncture: a radiological study

When lumbar puncture is performed in the sitting position, the patient's th ighs are usually at an angle of approximately 90 degrees to the trunk, wher eas in the lateral position, hip flexion is employed by flexing the patient 's knees to the chest. We measured the presumed but hitherto unquantified w idening of lumbar interspinous spaces resulting from hip flexion. Lumbar sp ine lateral radiographs were taken ill volunteers in the sitting position w ith and without hip flexion, and interspinous space width was measured and compared. Mean lumbar interspinous space width at L2-3, L3-4 and L4-5 incre ased by 7%, 11% and 21%, respectively, with the hips flexed. Hip flexion in the sitting position will anatomically optimise lumbar interspinous space width for needle passage, and statistically significant increases in space width have been demonstrated increasing progressively from L2-3 to L4-5.