Demographics of Our Lateral Access Classification System in Patient Populations at L4-5

Introduction: We previously published a classification system describing the varying anatomy of the retroperitoneal space, focusing on the great vessels and psoas/plexus. The goal was to standardize the anatomical differences seen in this space to allow for more communication between surgeons. In this study, we applied this classification system to patients from four different institutions over three geographic regions, specifically at the L4-5 level.

Methods: Data collection spreadsheets were distributed to four participating institutions. Patients seen at both neurosurgery and orthopedic spine clinics who had magnetic resonance imaging (MRI) performed as part of their workup were included in the study. Data were collected on age, gender, race, lumbar pathology, degenerative disc disease, spondylolisthesis, facet hypertrophy, and facet fluid. Vascular classification and psoas moderator were identified based on the classification schema from axial cuts of T2 weighted MRIs at the L4/L5 disc space on the left side.

Results: A total of 148 patients were included from the four participating institutions with an average age of 57 ± 16 years. There were significant differences in age (p < 0.01), race/ethnicity (p < 0.01), degenerative disc disease (p < 0.01), spondylolisthesis (p < 0.01), facet hypertrophy (p < 0.01), facet fluid (p < 0.01), and psoas moderator (p < 0.01) between the participating institutions. There were no significant differences in vascular classification (p=0.73), with Type I (n=116, 78%) being the most common, followed by Type II (n=29, 20%) and Type III (n=3, 2%). The vascular classification was found to be significantly associated with facet hypertrophy (p < 0.01), while the psoas moderator was significantly associated with institution (p < 0.01), degenerative disc disease (p < 0.01), and facet hypertrophy (p=0.02).

Conclusion : Applying our lateral access classification system, we found that approximately 50% of patients had an anterolateral psoas position and 78% of patients had safe Type I vascular anatomy. The next steps include applying the classification to surgical patients and correlating it with safety and outcome measures.