Assessment of Spinal Stability after Discectomy Followed by Annulus Fibrosus Repair and Augmentation of the Nucleus Pulposus: A Finite Element Study

Lumbar disc herniation (LDH) is a common condition which can lead to back pain. Although surgical treatments for LDH are well established, complications such as spinal instability and narrowing of adjacent facet joints are still frequently reported. The purpose of this study was to use finite element models to evaluate the stability of the L3–L4 segment after conservative or aggressive percutaneous transforaminal endoscopic discectomy (PTED) with and without an artificial material filler to correct LDH. Compared to the intact model, aggressive PTED reduced the stability of the segment (increased ROM) and narrowed the space between facet joints in the medial/lateral (ML) direction during flexion (maximum 6.7 degrees change in ROM and 90.5% spacing between facet joints), extension (maximum 2.1 degrees and 38.6%), and axial rotation (maximum 4.2 degrees and 90.1%). Aggressive PTED had a similar effect in the anterior/posterior (AP) direction during lateral bending (maximum 2.0 degrees and 44.2%). Augmenting the nucleus pulposus with a polyurethane filler after aggressive PTED improved spinal stability in both the ML and AP directions in all simulated motions, with results similar to the intact model. However, using a hydrogel filler did little to stabilize the spine, likely because the material is too soft to support the heavy, sustained loading. In conclusion, this study found that if an aggressive discectomy is required, augmenting the nucleus pulposus with a PU filler provides sufficient support to stabilize the spine, while hydrogel fillers offer little support.