Methods to determine the microscopic and macroscopic swelling behaviour of the annulus fibrosus

Mechanical and biological changes in the structure and function of the intervertebral disc (IVD) are thought to play a role in disc degeneration leading to low back pain. This study presents methods to investigate the macroscopic and microscopic swelling behaviour of the IVD. A biaxial loading apparatus mounted above an inverted confocal microscope was designed, built and tested. The apparatus enabled the precise loading of biaxial annular specimens to a desired strain setpoint, while monitoring applied force and visualizing in situ cells. The addition of a novel laser line sectioning tool allows for precise measurement of tissue thickness. Swelling behaviour was investigated for isolated cells. The isolation method was found to influence swelling behaviour. Results from swelling behaviour trials of isolated annulus cells may be used as a baseline from which to compare future in situ trials.