Thickness of the human ligamentum flavum as a function of load: an in vitro experimental study

Human cadaver spine specimens, consisting of the third and fourth lumbar vertebral laminae and the intervening ligamentum flavum, were studied. The specimens were loaded in axial traction with 1, 2, 4, and 8 kg respectively. To avoid contact deformation the thinning of the yellow ligament was recorded through an opto-electronic laser system. An average elongation of 6 mm was found at 8 kg of traction with a corresponding average thinning of 2 mm. The results indicated that the thickness changes of the ligamentum flavum might affect the dimensions of the lumbar spinal canal during, for example, normal changes in body posture.