Intervertebral disc herniation: studies on a porcine model exposed to highly repetitive flexion/extension motion with compressive force

Objective. To determine whether repeated motion with low magnitude joint fo rces, and flexion/extension moments consistently produce herniation in a no n-degenerated, controlled porcine spine motion segment. Design. Combined loading (flexion/extension motions and compressive forces) was applied to in vitro porcine functional spinal units. Biomechanical and radiographic characteristics were documented. Background. While most studies performed in vitro have examined uniaxial or fixed position loading to older specimens, there have been few studies tha t have examined whether 'healthy' intervertebral discs can be injured by lo w magnitude repeated combined loading. Methods. Porcine cervical spine motion segments (C3-C4) were mounted in a c ustom jig which applied axial compressive loads with pure flexion/extension moments. Dynamic testing was conducted to a maximum of 86 400 bending cycl es at a rate of 1 Hz with simultaneous torques, angular rotations, axial de formations recorded for the duration of the test. Results. Herniation (posterior and posterior-lateral regions of the annulus ) occurred with relatively modest joint compression but with highly repetit ive flexion/extension moments. Increased magnitudes of axial compressive fo rce resulted in more frequent and more severe disc injuries. Conclusions. The results support the notion that intervertebral disc hernia tion may be more linked to repeated flexion extension motions than applied joint compression, at least with younger, non-degenerated specimens. Relevance While intervertebral disc herniations are observed clinically, co nsistent reproduction of this injury in the laboratory has been elusive. Th is study was designed to examine the biomechanical response and failure mec hanics of spine motion segments to highly repetitive low magnitude complex loading. (C) 2001 Elsevier Science Ltd. All rights reserved.