Biomechanical Effects of Human Lumbar Discography: In Vitro Experiments and Their Finite Element Validation.

STUDY DESIGN: An experimental and computational finite element analysis of human lumbar spine discography and its resulting effects on disk biomechanics. OBJECTIVE: To characterize the changes in stress and displacement of the human lumbar spine disks after puncture due to discography. SUMMARY OF BACKGROUND DATA: Discography of the intervertebral disk (IVD) may be used to diagnose pathology of the disk and determine whether it may be a source for chronic back pain. It has recently been suggested that discography may lead to IVD degeneration, and has been a cause of controversy among spine care physicians. MATERIALS AND METHODS: Both in vivo experiment using cadaveric specimens and a finite element model of the same L3-L5 lumbar spine was developed using computed tomography scans. Discography was simulated in the model as an area in the disk affected by needle puncture. The material properties in the nucleus pulposus were adjusted to match experimental data both before and after puncture. RESULTS: Puncture of the IVD leads to increased deformation and increased stresses in the annulus fibrosis region of the disk. Pressure in the nucleus pulposus was found to decrease after puncture. Experimental and computational results correlated well. CONCLUSIONS: Puncturing the IVD changes disk biomechanics and hence may lead to progressive spine degenerations in particular in the punctured disks.