SPINE Volume 25, Number 23, pp 3036 –3044 ©2000, Lippincott Williams & Wilkins, Inc. The Effect of Disc Degeneration and Facet Joint Osteoarthritis on the Segmental Flexibility of the Lumbar Spine Atsushi Fujiwara, MD,* Tae-Hong Lim, PhD,* Howard S. An, MD,* Nobuhiro Tanaka, MD,* Chang-Hoon Jeon, MD,* Gunnar B.J. Andersson, MD, PhD,* and Victor M. Haughton, MD† Study Design. A biomechanical and imaging study of human cadaveric spinal motion segments. Objective. To investigate the effect of both disc degen- eration and facet joint osteoarthritis on lumbar segmental motion. Summary of Background Data. Spinal degeneration includes the osteoarthritic changes of the facet joint as well as disc degeneration. Disc degeneration has been reported to be associated with spinal motion. The asso- ciation of facet joint osteoarthritis with lumbar segmental motion characteristics and the combined influence of disc degeneration and facet osteoarthritis has not yet been investigated. Methods. A total of 110 lumbar motion segments (52 female, 58 male) from 44 human lumbar spines were studied (mean age = 69 years). Magnetic resonance im- ages were used to assess the disc degeneration from Grade I (normal) to Grade V (advanced) and the osteoar- thritic changes in the facet joints in terms of cartilage degeneration, subchondral sclerosis, and osteophytes. Disc height, endplate size, and facet joint orientation and width also were measured from the computed tomo- graphic images. Rotational movements of the motion segment in response to the flexion, extension, lateral bending, and axial rotational moments were measured using a three-dimensional motion analysis system. Results. Female motion segments showed signifi- cantly greater motion (lateral bending: P  0.001, flexion: P  0.01, extension: P  0.05) and smaller endplate size (P  0.001) than male ones. The segmental motion in- creased with increasing severity of disc degeneration up to Grade IV, but decreased in both genders when the disc degeneration advanced to Grade V. In male segments, the disc degeneration-related motion changes were signifi- cant in axial rotation (P  0.001), lateral bending (P  0.05), and flexion (P  0.05), whereas female segments showed significant changes only in axial rotation (P  0.001). With cartilage degeneration of the facet joints, the axial rotational motion increased, whereas the lateral bending and flexion motion decreased in female seg- ments. In male segments, however, motion in all direc- tions increased with Grade 3 cartilage degeneration and decreased with Grade 4 cartilage degeneration. Subchon- dral sclerosis significantly decreased the motion (female: axial rotation, P  0.05; extension, P  0.05 vs. male: flexion, P  0.05). Severity of osteophytes had no signif- icant association with the segmental motion. Conclusion. Axial rotational motion was most affected by disc degeneration, and the effects of disc degeneration on the motion were similar between genders. Facet joint osteoarthritis also affected segmental motion, and the influence differed for male and female spines. Further studies are needed to clarify whether the degenerative process of facet joint osteoarthritis differs between gen- ders and how facet joint osteoarthritis affects the stability of the spinal motion segment. [Key words: biomechanics, disc degeneration, facet joint osteoarthritis, lumbar spine, magnetic resonance imaging, segmental spinal motion] Spine 2000:25:3036 –3044 Degenerative disc disease is one of the major causes of back symptoms and is believed to be associated with segmental instability of the spine. 25,34 In 1982, Kirkaldy- Willis and Farfan 24 proposed three clinical and biome- chanical stages of spinal degeneration: dysfunction, in- stability, and stabilization. Spinal degeneration included disc degeneration (DD), facet joint osteoarthritis (OA), muscle alterations, and ligament degeneration. It was postulated that these changes would result in increased or abnormal segmental spinal motion. The intervertebral disc is a major component for seg- mental stability as well as a major load-bearing struc- ture. The effect of structural changes in the disc on the biomechanical characteristics of the spinal segment has been investigated for many years. 1,5,6,8,15,21,22,26,27, 31–33,36,37,41,46,51 Authors of these studies demonstrated that the degenerative changes in the disc are likely to render the lumbar motion segments more flexible. In most biomechanical studies of the effect of DD, however, the degenerative changes have been classified either by radiographs or by morphologic appearance of a horizon- tally sectioned disc. Limitations of such grading schemes include no assessment of changes in the endplate and vertebral body, insufficient categories to distinguish the wide range of appearances encountered, and the lack of tested validity of the classification system. Previous bio- mechanical studies also were limited in that the changes in segmental stability were investigated as a function of DD only, although spinal degeneration occurs in both discs and facet joints. Facet joints are true synovial articulations and un- dergo degenerative changes identical to those of OA seen in other synovial joints. 29,52 In general, a synovial joint with OA shows swelling, stiffness, deformity, instability, From the *Department of Orthopedic Surgery, Rush–Presbyterian–St. Luke’s Medical Center, Chicago, Illinois, and the †Department of Ra- diology, The University of Wisconsin Hospitals and Clinics, Madison, Wisconsin. Supported in part by National Institute of Health (NIH) grant ROI AR33667 and in part by OREF 96-040. Device status category: 1. Conflict of interest category: 14. 3036