Study design: An analysis of the vascular anatomy relative to the underlying discs in the lower lumbar spine performed by using radiologic studies.
Objective: To define better the vascular anatomy of this region from the perspective of the endoscopic spine surgeon, and to draw conclusions regarding surgical accessibility of the lower lumbar intervertebral discs.
Summary of background data: Cadaveric studies have highlighted the high degree of anatomic variability among the vascular structures overlying the anterior elements of the lower lumbar spine. An endoscopic approach to the intervertebral disc at these levels often is limited by arterial or venous structures. The growth of laparoscopic techniques to approach the intervertebral disc has renewed interest in the vascular anatomy of this region.
Methods: A computer-generated series of abdominal vascular studies performed for unrelated indications were scrutinized to ensure clear demarcation of the overlying vascular structures and underlying bony anatomy of the lumbar spine in a true anteroposterior plane. For analysis, 21 arterial (abdominal angiograms) and 22 venous (venograms) studies were selected. For the arterial data, level of aortic bifurcation and course of common iliac vessels were determined. The venous data were analyzed in a similar manner using the confluence of the common iliac veins as the major landmark. To draw conclusions about anterior surgical accessibility of the disc, the location of vessels was measured with respect to intervertebral disc spaces.
Results: The bifurcation level of the abdominal aorta was quite variable, occurring anteriorly to the L3 vertebral body in 3 of 21 studies (14%), and anteriorly to L4 and L5 in 10 (48%) and 7 (38%) of the studies, respectively. The cranial half of L5 was the most common single area of bifurcation (in one third of the studies). Venous anatomy was more consistent, with 86% of the patients displaying an iliac vein confluence at L5, and 14% having a confluence overlying L4. From an arterial perspective the L3-L4, L4-L5, and L5-S1 discs were readily accessible in 10%, 38%, and 95% of the studies, respectively. From a venous perspective, these levels were accessible in 100%, 73%, and 60% of the studies, respectively.
Conclusions: The results of this study suggest that a laparoscopic approach to the L3-L4 intervertebral disc will seldom be accomplished without significant retraction of the aorta. Access to the L4-L5 space will be accomplished readily in approximately one third of the patients. In the others, it will require significant vascular dissection. The L5-S1 space, conversely, will be readily accessible by the authors' definitions without significant vessel dissection in the majority of patients.