Introduction: Minimally invasive transforaminal interbody fusions can be performed with a unilateral facetectomy, bilateral facetectomy, or even a “partial bilateral facetectomy,” during which on one side a full facetectomy is performed for interbody access, while on the other side the facet capsule is drilled to loosen the facet and decorticate bone for arthrodesis. In this study, we evaluated the biomechanical outcomes of unilateral facetectomy (UF), partial bilateral facetectomy (PBF), and complete bilateral facetectomy (CBF).
Methods: 7 cadaveric specimens (L3-S1) were prepped for UF with full facet removal, hemilaminectomy, discectomy, and placement of pedicle screws (6.5X45MM) at L4-L5. Without rods, distraction was performed via an instrumented distractor tool (102N) and pure moment flexion (7.5Nm) test. A fixed interbody spacer was sized and placed into the specimen. Compression was then performed via an instrumented compressor tool(170N). Rods were locked into place via an instrumented compressor tool to 170N. Standard nondestructive flexibility tests (7.5Nm) were performed. Final lordosis angle was measured after rod lockdown with compression. Change in foraminal height was measured before and after posterior compression via compressor tool and final rod lockdown. The same procedure was performed for PBF and then CBF in all 7 specimens. Data was analyzed using RM-ANOVA (P< 0.05).
Results: CBF demonstrated significantly greater ROM(8.00±3.50) in pure moment distraction than UF(7.24± 3.33º)(p=0.026). With final rod lockdown, CBF demonstrated significantly greater change in mean foraminal height(1.90±0.62mm) than UF(1.00±0.45mm)(p=0.037). Final lordosis angle achieved was greatest with CBP(3.74±0.70), slightly less with PBF(3.11±1.22), and lowest with UF(2.68±1.28), with statistical significance between all three approaches(p< 0.04).
Conclusions: CBF allows greater ability to distract for interbody placement, greater lordosis angles with final screw lockdown, and increased foraminal height when compared to UF and PBF. CBF and PBF add time, effort, and slightly increased risk to the minimally invasive transforaminal interbody fusion, however, they may improve biomechanical outcomes.
Patient Care: Minimally invasive surgeons should use this data to best choose the type of facetectomy to perform in a given patient depending on the biomechanical outcomes that they desire to achieve.
Learning Objectives: To determine the biomechanical differences between unilateral facetectomy, bilateral facetectomy, and partial bilateral facetectomy in minimally invasive transforaminal interbody fusions.