Anatomy of Lumbar Interspinous Ligaments: Attachment, Thickness, Fibre Orientation and Biomechanical Importance

Literature related to the study of interspinous ligament in the lumbar region is sparse. Very few studies have elucidated the fibre orientation of this ligament at different lumbar levels. Male (19) and female (6) cadavers were dissected to expose the interspinous ligaments beneath all the lumbar vertebrae. Fibre attachments and directions were observed at all lumbar interspinous spaces. Thicknesses of the ligaments were measured at all levels. Interspinous ligament fibres were found to be oriented differently in the lumbar inter-spinous spaces. In the upper spaces the fibres were more horizontal. In the spaces beneath L3 and L4, fibres were curved and extended postero-superiorly. Fibres were thicker in the ligaments at the lower spaces in comparison to the upper ones. The mean thicknesses presented as: Upper (0.22 mm); Middle (0.37 mm) and L5-S1 (0.72 mm). Ligaments in the females were slightly thinner in comparison to the males. Fibres of inter-spinous ligaments were also found to attach to the inner aspects of the supraspinous ligament. Ligaments at L5-S1 junction were relatively vertical and stronger. None of the specimen demonstrated absence or cavitations of these ligaments except in a case with bi-laminar ligament at the L3-L4 level. The anatomy of the interspinous ligaments points to their probable role in graded restricting of acute flexion at the lumbar spine.