Introduction: A transitional vertebra is estimated to occur 4 to 30% in the general population. Lateral interbody fusion affords the ability to place a large graft to facilitate arthrodesis while minimizing ligamentous disruption and avoidance of neural element retraction within the spinal canal. The disadvantages are the proximity of the lumbar plexus and potential vascular injury particularly at L4-5 with complication rates ranging from 2 to 30%.
Methods: Retrospective study evaluating CT scans of the lumbar spine from 2010 to 2015 selecting
patients with transitional vertebrae. The following characteristics were evaluated: level of the iliac crest in relation to the L4-5 disc space, union level of the iliac veins and arteries, size of the L1-2, L2-3, L3-4, L4-5 disc, distribution of the iliac veins and IVC per the different Moro zones, distribution of the psoas muscle per Moro zones.
Results: 29 transitional patients: 12 males, 17 females with mean ages: males (46), females (54) and 29 nontransitional patients: 12 males, 17 females with mean ages: males (47), females (52).
Iliac crest location: Mean of 8mm above the L4-5 disc space in transitional patients compared with a mean of 4mm below the L4-5 disc space; p-value of 0.001. Iliac vein union: Mean of 6.5mm
above the L4-5 disc space in transitional vertebra patients compared with a mean of 2.5mm
below the L4-5 disc space in non-transitional patients.15% incidence of the iliac vein
entering Moro Zone 2 in the transitional patients compared to 0% in non-transitional
Conclusions: The Iliac crest is more likely to be above the L4-5 disc space, which makes it more
technically challenging via a lateral approach. The psoas muscle rises away
laterally and ventrally in transitional patients more often compared with non-transitional patients and this may result in a higher chance of vascular injury at the L4-5 level in transitional patients.
Patient Care: Increase the awareness by the surgeon in preoperative planning and imaging evaluation to perform safer surgery.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of the vascular and muscular differences seen in transitional patients. 2) Understand the segmentation the vertebral body by the Moro method.