The effect of scoliosis on surface landmarks for lumbar plexus block: a MRI-based retrospective case-control series

BACKGROUND:Degenerative scoliosis (DS) may affect surface landmarks for performance of lumbar plexus (LP) block. We hypothesized the extent of any difference in surface landmarks could be calculated by a formula based on measured degree of DS, body mass index, sex, and age. METHODS:We retrospectively searched our radiology database until 113 consecutive adult patients with DS were identified with lumbar spine radiographs and magnetic resonance imaging examinations performed. Pertinent surface landmark measurements at the L4 vertebral body level were recorded and compared to 50 controls. RESULTS:In patients with severe DS, there is a mean lateral deviation of the needle tip of 1.53 cm (0-3 cm) on the concave side and mean medial deviation of the needle tip of 0.35 cm (0-1.5 cm) on the convex side using typical bony landmarks. We found a significant correlation between body mass index and LP depth with a correlation coefficient ranging between 0.53 and 0.71. We found potential risk of organ injury in two of 13 patients with severe DS using traditional surface landmarks. CONCLUSIONS:There is a larger degree of lateral deviation of the LP on the concave side of scoliosis compared to medial deviation on the convex side. These deviations remained consistent irrespective of the direction of scoliosis. A review of the imaging studies and preprocedural ultrasound assessment of anatomy should be strongly considered prior to needle puncture. In patients with severe DS, an alternative approach may be considered to avoid the possibility of visceral organ injury.