NEW INSIGHT INTO THE MECHANICS OF THE LUMBAR INTERSPINAL LIGAMENT

Study Design. Repeated in vitro mechanical tests were performed on por cine and human interspinous ligament specimens with progressive disrup tion of the collagen fiber network to evaluate the existence of mechan ical interactions between collagen fibers. Objective. To evaluate the existence of a load pathway in the interspinous ligament whereby loads are transmitted between collagen fibers. Summary of Background Data. Mechanical tests demonstrate that the interspinous ligament resists sp inal flexion, but the collagen fibers are not oriented to oppose separ ation of the spinous processes. This seeming contradiction could be ex plained by the existence of mechanical interactions between collagen f ibers of the interspinous ligament. Methods. In vitro mechanical tests were performed on porcine and human bone-interspinous ligament-bone s pecimens. The collagen network of the ligament substance was disrupted by passing a scalpel blade though the ligament substance. Repeated te sts were performed with progressive disruption of the collagen fiber n etwork. Results. The stiffness of the interspinous ligament specimens was reduced as the collagen fiber network was disrupted, but approxima tely half of the initial stiffness was maintained when the collagen fi ber network was severely disrupted. In this case, no intact collagen f ibers remained. Conclusions. Mechanical interactions exist between col lagen fibers in the interspinous ligament. The mechanism of the intera ctions is unknown.