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ABSTRACT IntroductionThe intervertebral disc (IVD) of the bovine tail is a commonly used research analogue for the human disc at the organ, tissue, and cellular levels. While these tails are subjected to thousands of dynamic motion events daily, little is known about how these motions might induce tissue remodeling, particularly in the outer annulus fibrosus (AF) of IVDs connecting adjacent vertebrae. This study hypothesized that despite the similarities in geometry and biochemical composition of IVDs in the bovine tail, level‐wise variations in repetitive in‐vivo motion would be associated with tissue level adaptations. MethodsIn‐vivo active range of motion (RoM) was measured by placing inertial measurement unit sensors on the tails of adult cows and using a multi‐segment rigid body model to calculate level‐wise flexion‐extension and lateral bending angles. Level‐wise passive RoM was measured from cadaveric adult bovine tails in flexion, extension, and lateral bending with skin and muscles removed. IVDs were extracted for measurement of height, diameters, AF radial thicknesses, and AF fiber crimp periods. ResultsIn‐vivo joint RoM was found to vary drastically by level, largely due to a prominent second order mode with inflection point at the fourth joint. Joint levels near this inflection point were found to have the highest passive RoMs. In the proximal tail, decreased RoM was associated with an increased fiber crimp period in the outer AF, while in the distal tail it was associated with increased AF thickness. DiscussionTaken together, these findings suggest that IVDs in the bovine tail respond to repeated complex dynamic motions through a process of adaptation at the mesoscale (AF thickening during growth) and microscale (residual strain accumulation in the mature state). The bovine tail thus provides a powerful tool for modeling how the human lumbar intervertebral disc may remodel in response to changes in exposure to repetitive motions. 

Abstract Intradiscal injection is required to deliver therapeutic agents to the intervertebral disc (IVD) nucleus pulposus (NP). However, injectate leakage following needle retraction may result in decreased treatment efficacy and adverse side effects. While enzymatic digestion is a common research approach for simulating degeneration in healthy animal IVDs, contributions to the leakage phenomenon are unknown. In this study, bovine caudal discs were treated with injection into the NP of either a tris buffer control, collagenase (to primarily target collagen), or trypsin (to primarily target proteoglycans) and then injected with fluorescent saline using a through-puncture defect protocol. Pressure–volume records during injection were used to determine volume and pressure at leakage. Discs were then frozen, transected, and photographed to visualize injectate dispersion. Collagenase treatment resulted in a large increase in injectate dispersion, along with a decrease in injection pressure relative to control. Trypsin treatment resulted in a moderate increase in dispersion, with no associated effect on pressure. This study concludes that care should be taken when employing enzymatic digestion to simulate IVD degeneration, as NP tissue disruption may affect both retention and dispersion of subsequent therapeutic injections.