SUMMARY On polarization microscopy collagen fibres from human cadaveric anterior longitudinal, posterior longitudinal, and interspinous ligaments show a series of transmission and extinction bands. By observing changes in this pattern on rotating the polarizing stage and on rotating the fibres a crimped structure of the fibres was deduced and its parameters were calculated. From these data the force/strain behaviour of the fibres under low tension was calculated. This corresponded closely with the results from mechanical measurement. At the same time we documented alterations in the transmission and extinction patterns while under tensile load. The results suggest that it is the crimped structure that is responsible for the high extensibility of the collagen fibres under low tension. The initial extension is by deformity of the crimp segment. This avoids risk of tearing the collagen fibres.In life the ligaments of the human vertebral column are commonly loaded in tension. We report the force/strain behaviour of the fibres from human anterior longitudinal ligaments, posterior longitudinal ligaments, and interspinous ligaments at low tensions. The results obtained are compared with those predicted from a mechanical model. The model closely resembles the structure of the fibres deduced from separate microscopy experiments.
MethodsAt autopsy the lumbar spines were removed intact from 2 previously healthy males aged 35. and 41 years, who died shortly after road traffic accidents Accepted for publication June 30, 1976 Correspondence to Dr. M. I. V. Jayson, Department of Medicine, Bristol Royal Infirmary, Bristol BS2 8HW without spinal injury. Fibres were sampled from the anterior longitudinal, posterior longitudinal, and interspinous ligaments at the level of the 1st and 2nd lumbar vertebrae. Individual fibres were extracted by carefully teasing apart the surface layers of the ligaments with dissecting needles and then gently pulling them in the direction at right angles to the surface of the tissue. The separated fibres were stored in iso onic saline at -25°C until ready for use. Three fitres from each of the three ligaments of the two spines, making a total of 18 fibres, were subjected to the following experiments.We placed each fibre between the crossed filters of a polarizing microscope with its long axis parallel to the axis of polarization of one of the filters. Along the length of each fibre a series of transmission and extinction bands were seen and an example is shown in Fig.