Why is Denticulate ligament important for Neurosurgeons ?

Denticulate ligaments are tooth like lateral projections of the spinal pia mater which attach to the dura mater on the either side of the spinal cord. There are 21 such pairs of denticulate ligaments. 

As the denticulate ligament extend along the length of spinal cord to the dura on either side they serve as an important landmark for the neurosurgeon to identify anterior (motor) nerve roots and posterior (sensory) nerve roots of the spinal cord. A neurosurgeon who wants to operate on the motor roots operates anterior to the denticulate ligament whilst the one who want to operate on sensory roots limits his surgery posterior to the denticulate ligament.