The objective of this study was to determine the anatomy and mechanics ot the lumbar interspinous ligament. Particular focus was on the collagen fibre orientation within the interspinous ligament, and on direct comparisons between porcine and human specimens.

The first experiment involved mechanical testing of isolated interspinous ligament specimens to evaluate whether this ligament resisted separation of the spinous processes, as occurs with spinal flexion. This study determined that the interspinous ligament resists spinal flexion, and inferred that mechanical coupling exists between collagen fibres in the interspinous ligament, although the mechanism of this coupling was unknown. This study prompted a more detailed investigation of the anatomy and collagen fibre orientation in the interspinous ligament.

The second report described a novel apparatus and software developed for quantifying two-dimensional collagen fibre orientation. This approach was unique in that it was semi-automated, and it quantified the collagen fibre orientation across the entire specimen.

This technique required that the tissue was strained in order that the natural crimp of the collagen fibres was straightened. An appropriate spine testing machine was designed and built. This machine applied continuous pure flexion moments, extending upon the accepted technique of pure moment testing using discrete loads.

In addition, the flexion mechanics of human and porcine lumbar spines are reported in an Appendix. The porcine and human specimens showed similarities in mechanical behaviour, however the porcine specimens demonstrated a less-stiff, more extensive, low-stiffness region around the neutral position.

The final study described the collagen fibre orientation of the interspinous ligament. This study provided quantitative collagen fibre orientation data which indicated that the ventral and middle regions of the interspinous ligament are composed of loose collagen with a broad orientation distribution, and therefore these regions do not have a role in flexion mechanics. In contrast, the dorsal region was composed of dense collagen oriented at approximately 74-79 degrees with respect to the mid-disc plane. This component was similar in the porcine and human interspinous ligament. This dorsal region has a long moment arm and therefore effectively prevents excessive flexion.