Mechanism of failure of the ligamentum flavum of the spine during in vitro tensile tests.

Abstract

Thirty ligamenta flava were dissected from pig lumbar spines with their attachments to the bone of the laminae still intact. These specimens were tested to failure, in tension, at strain rates of 0.03 and 0.2 s-1. Video recordings were made of the specimens during testing. Specimens failed because the ligaments became detached from the bone. The maximum stress that the ligaments were able to transmit was approximately 3 MPa. However, the corresponding strain was higher when testing at the slower strain rate than at the faster rate; these strains were 1.6 +/- 0.5 and 1.0 +/- 0.3, respectively. All specimens were able to transmit stress after the maximum value had been attained because threads of ligament continued to remain attached to bone. Complete failure did not occur until the last of these threads had pulled away. Scanning electron micrographs showed no ligament, other than a few isolated pieces of fibre, adhering to bone after failure had occurred.