Strain relates connective tissue properties to joint movement

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

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.

Stress in collagen fibrils of articular cartilage calculated from their measured orientations

Articular cartilage may be considered as a form of pressure vessel in which the internal swelling pressure is balanced by tensile stress in the collagen fibrils. This stress is calculated by analysing the tissue as a series of microscopically small pressure vessels. The previously measured orientations of the collagen fibrils describe the structure necessary for this calculation. The stresses and strains developed in the fibrils are shown to be well within physiological limits.