Anatomical landmarks based assessment of intravertebral space level for lumbar puncture is misleading in more than 30%.

BACKGROUND The anatomical landmark which is used to identify the correct level for lumbar puncture is the line connecting both iliac crests. This crosses the vertebra column at the level of the L4-L5 intervertebral space or L4 vertebra. It can be difficult to determine in a group of orthopaedic patients due to chronic orthopaedic disorders, chronic pain, overweight, or difficulties with positioning for lumbar puncture. The objective of this study was to determine if identification of intervertebral space by a physical exam differs from that of an ultrasound assessment. METHODS Adult patients scheduled for lower limb surgery under spinal block were enrolled in this study. The intervertebral space suitable for lumbar puncture was determined by physical exam by an anaesthetist in the sitting or lateral position. This was followed by a lumbar ultrasound. Primarily, a transducer was placed in paramedian sagittal view followed by transverse interlaminar view to confirm the identification of the interlaminar spaces. The 'counting-up' approach starting with the L5-1 space was applied. RESULTS One hundred and twenty two patients (122) were included in this study. Lumbar intervertebral spaces were identified by ultrasound in all cases. There was concordance of intervertebral space identification (between clinical and ultrasound examination) in 78 cases (64%). Mean deviation of inacuracy was one intervertebral space with no statistical difference among cephalad and caudal direction. There were no statistically significant differences fund in terms of demographic data (sex, age, height, weight, or BMI), positioning for lumbar puncture, or intervertebral space chosen for the puncture between the concordant and the nonconcordant identification groups. The only statistically significant difference found was the difference in the years of experience of the anaesthetist performing the clinical assessment and puncture. CONCLUSIONS The concordance rate between clinical examination and using assessment of intervertebral space identification for lumbar puncture is 64% among patients undergoing lower limb surgery. No special parameters were found which could make an anaesthetist aware that a patient is at greater risk of inadequate intervertebral space level assessment. Spinal ultrasound can reduce the incidence of inappropriate lumbar puncture level in orthopaedic patients.