Does lumbar microdiscectomy affect adjacent segmental disc degeneration? A finite element study

Background: Microdiscectomy is a common surgical procedure used to treat lumbar disc herniation. Following microdiscectomy, the space of the excised nucleus pulposus is replaced by fibrocartilaginous granulation tissue. This results in alterations of both the material properties of the intervertebral disc and the biomechanics of the lumbar motion segments, potentially contributing to adjacent segmental disc degeneration. To our knowledge, there is no published study in the English literature investigating this potential effect. Materials and methods: A previously developed three-dimensional finite element model of L3-L5 was used as a normal control. From this normal model, two different grades of disc degeneration models (mild and moderate) and corresponding microdiscectomy models were developed by changing either the geometry or associated material properties of L4-L5 segment. The 800 N pre-compressive loading plus 10 Nm moments simulating flexion, extension, lateral bending, and axial rotation were imposed on L3 superior end plate of each model. The intradiscal pressure, intersegmental rotation, and tresca stress of annulus fibrosus in L3-L4 segment were investigated. Results: The intradiscal pressure, intersegmental rotation, and tresca stress of L3-L4 segment in mild degeneration microdiscectomy model are higher than those in the mild degeneration model under all motion directions. The above parameters in moderate degeneration microdiscectomy model present a similar trend to the mild degeneration microdiscectomy model. However, the intersegmental rotation of L3-L4 in moderate degeneration microdiscectomy model is lower than that in the moderate degeneration model in lateral bending, and the intradiscal pressure of L3-L4 in moderate degeneration microdiscectomy model is lower than that in the moderate degeneration model in axial rotation. Conclusions: Lumbar microdiscectomy can result in altered biomechanics, which may have an adverse effect on the development of adjacent upper segmental disc degeneration. (C) 2013 Elsevier Inc. All rights reserved.