Biomechanical evaluation of graded ventralfacetectomy simulating foraminoplasty of percutaneous endoscopic lumbar discectomy.

OBJECTIVE: To explore the lumbar spine biomechanics of graded ventral facetectomy and determine the appropriate extent of resection for foraminoplasty. PATIENTS AND METHODS: We retrospectively measured several radiological parameters of superior articular process (SAP) and bony intervertebral foramen in computed tomography scans of 170 lumbar vertebral discs. The intact finite element (FE) spine of L2-sacrum was modified to simulate foraminoplasty with two typical graded ventral facetectomy methods (Method Ⅰ: basal part resection of SAP; Method Ⅱ: apical part resection of SAP) to explore the biomechanical effects under different physiological motions. RESULTS: Examination of the radiological parameters of the bony intervertebral foramen indicated that they were generally narrower than the diameters of commercially available working cannulas. Some of these parameters showed gender differences. The biomechanical evaluation indicated that the range of motion increased gradually with the expansion of the resection extent, and the differences compared to the intact spine at the same level were greater in Method I than in Method Ⅱ. CONCLUSIONS: The appropriate ventral resection extent of the basal part of the SAP (Method I) was 4 mm, 3 mm, and 3 mm on the lateral view at L3-L4, L4-L5, and L5-S1, respectively. The appropriate ventral resection extent of the apical part of the SAP (Method II) were 10 mm, 6 mm and 6 mm on the lateral view at L3-L4, L4-L5, and L5-S1, respectively. Extensive resection of foraminoplasty may destabilize lumbar motion segments.