AN L4-L5 slip disc (herniated or bulged) can impinge (compress) the thecal sac (spinal cord fibers) and spinal nerves. The slightest amount of compression or impingement on a nerve or spinal cord fibers is significant. Nerve compression is significant because it causes nerve degeneration. Narrowing (stenosis) of bony openings for nerves due to the presence of bone spurs (abnormal bone growth) or other degenerative changes may cause compression of the nerve roots in the area of stenosis.