Often a disc bulge occurs in a patient with “degenerative arthritis” known as Osteoarthritis. (This is to be distinguished from Osteoporosis, which is the thinning of bones due to loss of calcium, and which usually occurs in genetically predisposed post-menopausal women.) In the illustration below, the facet joint has become large (hypertrophied) and developed bony spurs, i.e. it is osteoarthritic.
Now the nerve no longer has enough room to exit the spinal canal, and sciatica with varying degrees of pain, numbness, and weakness will be present.
Stenosis occurs whenever the spinal canal or the hole a nerve root exits (foramina) the spinal canal is narrowed. In the above illustration, the foramina was tight (i.e., stenotic!) prior to the disc herniation. Thus a person with stenosis is more likely to be symptomatic from even mild disk herniations. Click to learn more about the various types of stenosis.
Thus the incompetent disc and the bulging herniated disc accompanied with severe enough osteoarthritic changes, will require surgery to correct.