181. Sequential changes in lumbar lordosis and segmental stability following lateral interbody cage placement, Smith-Peterson Osteotomy, and anterior longitudinal ligament release

Abstract

BACKGROUND CONTEXT Interbody cage systems can be used in isolation to achieve lumbar lordosis correction, but can also be deployed using techniques to shorten the posterior or lengthen the anterior spinal column to yield even larger corrections. The Thomasen pedicle subtraction osteotomy (PSO) yields ∼30° of correction but with high degree of difficulty and surgical complication rates. A lateral lordotic cage with Smith-Petersen Osteotomy (SPO), a hyper-lordotic lateral cage with anterior longitudinal ligament (ALL) release, or a lateral cage with combined techniques show potential for substantial lordosis correction. The removal or release of local spinal anatomy, however, can increase segmental motion and may inhibit fusion. The objective of this biomechanical cadaver study was to identify the lordosis correction and resulting segmental stability achieved with implantation of lateral lordotic cages of increasing angle coupled with either or both minimally invasive surgical techniques of ALL release and SPO. We hypothesize that a combination of lordotic interbody cage placement, ALL release and SPO will yield more lordosis at a single level than with either of these interventions in isolation, and the biomechanical stability of the construct will be sufficiently rigid to promote fusion. METHODS Cadaveric lumbar spines (n=6) were divided into L1-L2 and L3-L4 segments, potted in plaster with pedicles exposed and randomly distributed to treatment groups (n=6 segments/group) consisting of eight interventions. Native lordosis and range of motion (ROM) were recorded prior to intervention. Within each treatment group, lateral cages of 8°, 20°, and 30° were placed and backed up with posterior spinal fixation, a 1-hole modular fixation plate was added with ALL release, and was replaced by a 2-hole plate at the last intervention. Treatment groups were designed to test procedure order; in Group 1, SPO with an 8° cage preceded ALL release with a 20° cage, and in Group 2, ALL release with a 20° cage preceded SPO with a 30° cage. Sagittal fluoroscopic images for lordosis angle measurement and ROM data were collected after each intervention. 7.5Nm pure moments were applied to segments in flexion-extension (FE), lateral bending (LB), and axial rotation (AR), while optical motion capture recorded ROM. Linear mixed models with repeated measures provided statistical comparisons at α=0.05 within each group for each metric (angle, FE-, LB-, AR-ROM); data reported as percent of native. RESULTS The combination of SPO with ALL release yielded the largest lordotic angle regardless of procedure order (correction angle: 28.5°±7.3°), but also greatest ROM in all planes (FE: 61.5%±48.4%, LB: 42.2%±42.0%, AR: 162.8%±178.3%). A 30° cage provided no additional gain in lordotic angle and increased ROM in FE and AR with ALL release and SPO (FE: 36.8%±27.1%, AR: 144.3%±138.6%). An 8° lordotic cage with SPO achieved the largest angle correction (10.1°±6.8°) while reducing ROM in all planes. Addition of a 2-hole plate does not decrease correction and tends to reduce ROM in all planes compared to the 1-hole plate. CONCLUSIONS Lordosis >15° is possible through minimally invasive techniques of SPO and ALL release and performing a SPO without ALL release yields substantial correction without compromising stability. Performing a SPO after ALL release increases segment ROM in FE, LB, AR, thus a 2-hole plate is recommended to aid in stability with ALL release. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.