Degeneration of the lumbar spine is a common cause of low back pain, with both intervertebral disc pathology and facet joint osteoarthritis contributing to altered spinal biomechanics. This kinematic MRI study evaluated the relationship between L5/S1 intervertebral disc degeneration, facet joint osteoarthritis, and segmental motion parameters in 214 patients presenting with low back pain. Disc degeneration was graded using the Pfirrmann classification, while facet joint degeneration was assessed using the Pathria scale, alongside measurements of facet joint angle, joint space width, and segmental angular and translational motion.

The results demonstrated a significant association between L5/S1 disc degeneration and increased facet joint osteoarthritis. Patients with more advanced disc degeneration had higher odds of facet joint OA (OR = 2.28), and a positive correlation was observed between disc and facet degeneration severity (r = 0.365). Notably, severe facet joint osteoarthritis (grade IV) was absent in patients with mild disc degeneration. Additionally, facet joint space width decreased significantly as disc degeneration progressed, indicating structural narrowing with worsening degeneration. However, facet joint angle and segmental spinal motion parameters (angular and translational motion) did not show statistically significant differences across degeneration grades.

These findings suggest a closely linked degenerative cascade between the intervertebral disc and facet joints at the L5/S1 level. As disc degeneration progresses, increased mechanical stress may contribute to facet joint degeneration and narrowing of the joint space. While structural changes were clearly associated with worsening disc pathology, overall segmental motion remained relatively preserved across degeneration grades. This supports the concept of coupled disc–facet degeneration in lumbar spondylosis and highlights the importance of considering both structures when evaluating and managing degenerative lumbar spine conditions.