Effect of Percutaneous Endoscopic Lumbar Foraminoplasty of Different Facet Joint Portions on Lumbar Biomechanics: A Finite Element Analysis

OBJECTIVE: To evaluate the influence of percutaneous endoscopic lumbar foraminoplasty of different facet joint portions on segmental range of motion (ROM) and intradiscal pressure (IDP) of L(3)/L(4) and L(4)/L(5) motion segments by establishing three dimensional finite element (FE) model. METHOD: Computed tomography images of a male adult volunteer of appropriate age and in good condition both mentally and physically. Obtained data was used in this study from July 2020 to December 2020, and an intact L(3–5) three dimensional finite element model was successfully constructed using ANSYS and MIMICS software (model M1). The M1 was modified to simulate the foraminoplasty of different facet joint portions, with unilateral cylindrical excision (diameter = 0.75 cm) performed on the tip (model M2) and the base (model M3) of right L(5) superior facet elements along with surrounding capsular ligaments, respectively. Under the same loading conditions, the ROM and IDP of L(3)/(4) and L(4)/L(5) segments in states of forward flexion, backward extension, left lateral bending, right lateral bending, left axial rotation and right axial rotation were all compared. RESULT: Compared with the intact model in backward extension, M2 increased the ROM of L(4/5) segment by 9.4% and IDP by 11.7%, while the ROM and IDP of M3 changed only slightly. In right axial rotation, M2 and M3 increased the ROM of L(4/5) segment by 17.9% and by 3.6%, respectively. In left axial rotation, M2 and M3 increased the ROM of L(4)/L(5) segment by 7.14% and 3.6%, respectively. As for other states including forward flexion, left lateral bending, right lateral bending, the ROM and IDP were not significantly distinct between these two models. While focusing on L(3)/L(4) segment, obviously changes in the ROM and IDP have not been presented and neither M2 nor M3 changed in any loading condition. CONCLUSION: This study provides evidence that the base‐facet foraminoplasty of L(5) superior facet provided a higher segmental stability compared with the tip‐facet foraminoplasty in flexion and axial rotation. Meanwhile, it also shows the two types of foraminoplasty make few differences to the L(4/5) segmental biomechanics. Besides, it does not appear to impact the stability of L(3)/L(4) in six states of forward flexion, backward extension, left lateral bending, right lateral bending, left axial rotation and right axial rotation when superior facet of L(5) was partially removed. These findings might be useful in understanding biomechanics of the lumbar spine after foraminoplasty performed on different portions of the facet, thus providing endoscopic surgeons a better reference for operational approach to maintain the function and mobility of the spine.