1222 Biomechanical Restoration in Unilateral Facet Arthroplasty Compared to Bilateral Facet and Total Posterior Arthroplasty: A Cadaveric Evaluation

INTRODUCTION: The facet joints are implicated in approximately 15-45% of low back pain. Pathology involving or requiring intervention through the facets, such as spondylolysis, foraminal stenosis, and disc herniation are typically unilateral. METHODS: 7 cadaveric L3-Sacrum specimens were tested within the multidirectional bending model between 0 to ±10 Nm in flexion-extension (FE), flexion-extension with 400N of compressive follower load (FE-FL), axial rotation (AR), and lateral bending (LB). We measured the L4-L5 range of motion (ROM), intradiscal pressure, and contralateral facet load. Each specimen was tested in intact (I), capsulotomy (C), medial facetectomy (MF), total facetectomy (TF), and UFA conditions, during which load transfer at the bone-implant interface was measured. RESULTS: UFA significantly restored 93% (FE), 77% (FE-FL), 123% (AR), and 106% (LB) of the native range of motion (p<0.05). UFA significantly restored the native intradiscal pressure during compressive follower load (I:173 ± 67KPa vs TF:103± 82KPa vs T:174 ± 69KPa), and partially during contra-axial rotation ((I:32 ± 27KPa vs TF:81 ± 55KPa vs T:59 ± 46KPa) (p<0.05). No significant changes were observed in the contralateral facet load. Contra-axial rotation induced the largest loads on the bone-implant interface. CONCLUSIONS: While equivalent in other motion planes, UFA produces superior FE restoration to BF (93% vs 51%), and superior AR restoration to TP (123% vs 47%). UFA also restores intradiscal pressure at the intact level and supports 50% less load at the bone-implant interface than TP.