The umbilicus and pelvic incidence to inform surgical incisions for anterior lumbar interbody fusions: A radiographic analysis.

Purpose: To radiographically assess the umbilicus' level (i.e. latitude) relative to the anterior lumbar spine based on varying pelvic incidence (PI) magnitudes.

Methods: Pediatric patients (ages 10-18 years) with a previously obtained CT abdomen/pelvis were reviewed. Excluded were patients with prior spine surgery, spinal deformity, and/or underlying lumbar spinal degenerative pathology. On sagittal CT images, 2 radiologists recorded the vertebral level/disc space that corresponded to the umbilicus' latitude level. On the CTs' scout lateral images, two spine surgeons measured the PI. The spinal level corresponding to the umbilicus' latitude was compared between 3 groups based on PI magnitude: low (< 45°), middle (45°-65°), and high (65°).

Results: 107 patients (average age = 14.82.0 years; 62.6% female; average BMI=25.9±10.1) met inclusion criteria. Of all patients, the umbilicus' level ranged from the L3-4 disc to the L5 vertebral body with the L4-5 disc (36.4%) and L4 vertebral body (29.0%) being the most common levels. Average PI was 47.2° 11.9° (Low PI-41.1%; Middle PI-46.7%; High PI-12.1%). The umbilicus' level relative to the spine significantly varied based on PI magnitude (p<0.001). In Low PI, the majority's umbilicus corresponded to the L4-5 disc (50%) or L5 vertebral body (18.2%). In Middle PI, the majority's umbilicus was at the L4 vertebral body (34.0%) and L4-5 disc (34.0%). In High PI, the majority's umbilicus corresponded to the L3-4 disc (38.5%) or L4 vertebral body (46.2%).

Conclusions: The umbilicus' level relative to the lumbar spine significantly varies based on PI magnitude. Patients with lower PIs (low sacral slope) have their umbilicus more commonly located over the distal lumbar spine (L4-5 disc/L5 vertebral body), while high PI patients (high sacral slope) have more superiorly located vertebral levels when referencing the umbilicus. Additional clinical investigations will be beneficial to confirm utility of these findings in guiding location of ALIF incisions.