General Session: Biomechanics
Presented by: P. Zhou - View Audio/Video Presentation (Members Only)
A. Patel(1), J. Oh(1), D. Leven(1), F. Cautela(1), D. Chatterjee(1), Q. Naziri(1), F. Langella(2), B. Diebo(1), C. Paulino(1)
(1) SUNY Downstate Medical Center, Orthopaedic Surgery, Brooklyn, NY, United States
(2) Second University of Naples, Naples, Italy
Background: Minimally Invasive Surgery (MIS), notably lateral lumbar interbody fusion (LLIF), is increasingly recognized as a surgical option for adult spinal deformity (ASD) patients. Despite an increase in the prevalence of ASD in recent years, anatomical studies related to LLIF safety have thus far been limited to subjects free of rotational deformity. Lumbar plexus (LP) anatomy modifications may occur in these spinal deformity patients. We aimed to investigate the impact of vertebral axial rotation (VAR) on the neurovascular anatomy in patients with spinal deformity. Adolescent idiopathic scoliosis (AIS) patients were selected to isolate vertebral rotation analysis without confounding the findings with typical superimposed degenerative cascade observed in adulthood. With the data gathered, we also aimed to provide recommendations on the approach based on the degree of axial rotation observed.
Methods: This study is a retrospective radiological case series. MRI scans (L1-S1) from fifty rightconvex thoracic (left-convex lumbar) AIS patients were analyzed. The anterior vertebral body (AVB) axis was used to provide a reference line. At each intervertebral level, vertebral rotation (VR), lumbar plexus depth (LPD), and vascular structure depth (VSD) were evaluated. Paired t-test analyses were used to describe anatomic differences between the concave and convex aspect of our patients´ curves. Correlation analysis was used to investigate relationships with soft tissue modifications and vertebral rotation.
Results: Fifty AIS patients (17M, 33F) with a mean thoracic Cobb of 50.6° ± 17.0° and a mean lumbar Cobb of 41.9° ± 13.0° were included for analysis. Mean VR at each level was L1-2=-6.6°, L2-3=-7.7º, L3-4=-6.5º, L4-5=-4.7º, L5-S1=-2.6º (negative value denotes clockwise rotation). We found significant differences (p< 0.05) between concave-convex (right-left) LPD at each level (L1-2=3.7mm, L2-3=5.1mm, L3-4=4.2mm, L4-5=2.2mm, L5-S1=2.2mm). VSD was significantly different at L1-L2 (3.2 mm) and L5- S1 (3 mm). A significant correlation was found between increasing vertebral rotation and concave-convex lumbar plexus depth difference (r=0.68, p< 0.001).
Conclusions: While the lateral transpsoas approach to the lumbar spine is a useful tool in the spine surgeon's arsenal, it is not acceptable to perform LLIF without addressing patient specific deformity. This study demonstrates that displacement of the lumbar plexus is tied to the magnitude of vertebral rotation in patients with adolescent idiopathic scoliosis. When approaching the lumbar spine in this patient group, this displacement widens the safe surgical corridor on the convex side and narrows the corridor on the concave side. Careful review of a patient's MRI scans should occur preoperatively to assess their individual safe surgical corridor for the LLIF approach. Adult spinal deformity surgeons who approach a degenerated spine in patients with progressive AIS in adulthood must carefully plan for patient positioning, neurovascular anatomy and realignment objectives prior to the day of surgical intervention.