Predicting the Depth of the Lumbar Plexus in Pediatric Patients: A Retrospective Magnetic Resonance Imaging Study.

Background: The lumbar plexus (LP) block is commonly used for analgesia for lower extremities. If the depth of the LP (LPD) can be predicted, the performance time and procedure-related complications could be reduced.

Methods: Three hundred sixty-one magnetic resonance images of pediatric patients (<18 years of age) were analyzed. Simple linear regression and multiple linear regression analyses were performed to predict the LPD using patient age, weight, height, and the distance between the midline and posterior superior iliac spine (midline-PSIS). The ratio of the distance between the midline and the most lateral aspect of the LP (midline-LP) to midline-PSIS (midline-LP/midline-PSIS ratio) was calculated to suggest a needle insertion point at the L4/L5 intervertebral level. The presence of the kidney at the L4 level and the L4/L5 intervertebral level was determined.

Results: The LPD at the L4/L5 intervertebral levels was predicted using the equation LPD = 0.844 × weight (kg) + 25.8 (mm) in pediatric patients <18 years of age (r = 0.791; 95% confidence interval [CI] of r, 0.753-0.829). The overall midline-LP/midline-PSIS ratio was 0.87 (95% CI, 0.86-0.89), and the ratio was higher in neonates and infants (0.98 [95% CI, 0.95-1.02]) than in the other age groups. The presence of the lower kidney pole at the L4 level was common in pediatric patients (43.7% of neonates and infants and 13.7% of toddlers and preschool-aged children). The lower kidney pole was observed at the L4/L5 level in 6 patients (1.7%).

Conclusions: When LP block is performed in pediatric patients, the LPD and risk of renal injury should be considered for successful and safe analgesic block.