Can cervical disc herniations be provoked

Introduction: Neck pain, one of the leading causes of physical disability, can be caused by cervical disc herniation. The purpose of this Methods: Six cervical motion segments (3x C4-C5, 3x C6-C7) from four human donors (19-58 years) with Miyazaki degeneration grades II-IV were included. A novel test method was developed to simulate complex neck motions occurring during typical daily-life activities using a dynamic disc loading machine. Long-term effects were simulated by exaggerating and combining these motion patterns. The specimens were subjected to the dynamic loading protocol (n = 3,000 cycles) in the intact state, after 1 mm incision in the posterior longitudinal ligament (PLL), and after complete transection of the PLL. Quasi-static flexibility testing was performed before and after each testing step. For microstructural investigations, histological analysis was performed by cryosectioning three C6-C7 discs. Results: Using the dynamic loading protocol alone, no herniation could be provoked in intact specimens. Only after the PLL was injured (1 mm incision), a clear prolapse with nucleus extrusion through the defect (n = 1) as well as a protrusion (n = 1) were identified, while complete transection of the PLL did not cause further herniations. Both specimens were less degenerated and from young donors. The extrusion led to a slight increase in range of motion by about 1° in each motion direction. Histological analysis revealed microstructural damage in nucleus pulposus and posterior annulus fibrosus fibers, along with nucleus material flowing through the ruptured annulus in both herniated specimens. Discussion: Using this novel test method, the simulation of physiological, long-term loading of human cervical discs is feasible. In general, an intact cervical disc does not seem to herniate due to daily-life activities, even under long-term complex motions. The PLL appears to have a main protective effect on the cervical disc, because a herniation only happened when an artificial defect was created. Moreover, the risk of cervical disc herniation might be highest in young patients with low disc degeneration.