Biomechanics of the iliolumbar ligament

Abstract

The contribution of the iliolumbar ligament to the stability of the lumbosacral junction was studied in fresh human cadaveric spines. A first test apparatus was constructed to study the effect of division of the ligament on the mobility of the L5-S1 junction during flexion, extension, lateral bending and axial rotation. It was found that at 6 Nm of loading, flexion of L5 and S1 was significantly restrained by both bands of the ligament while lateral bending was mainly controlled by the anterior band. The effect of the ligament on extension of the lumbosacral junction was minimal and that on axial rotation was not apparent at 6 Nm loading. A second test apparatus was designed to test the torsional stability of the lumbosacral junction until failure. The ligament was found to contribute to 35.2% of the normalized elastic strain energy of the lumbosacral junction in axial rotation. It is felt that the iliolumbar ligament contributes significantly to the stability of the lumbosacral junction and it is important in protecting the lumbosacral disc from excessive torque.