The L4 and L5 vertebra and associated discs contribute to 50% of the lumbar lordosis. Compression of the trapezoidal body of L5 can significantly reduce this and alter the biomechanics at L4/5 and L5/S1. A narrow or trefoil spinal canal will expose traversing and exiting nerve roots to trauma and the potential for isolated root injury in burst fractures or fracture dislocation. The seating of the lumbosacral junction within the pelvis, the ilio–lumbar ligaments and the major muscle support groups require high level energy transfer to result in major injury to the low lumbar spine.
The posterior approach to the spine is well know to all surgeons, but the anterior approach to L4 and L5 can be difficult with the great vessels adherent to the bony structures at these levels. While anterior access to the L4/5 and L5/S1 disc is frequently performed, access to the body is more difficult. Anterior stabilising devices that are bulky cannot be used in this region because of the anterior vascular anatomy (Acromed Publications).