Degenerative disc disease refers to dehydration and shrinkage of the intervertebral discs that cushion the vertebral bodies of the spine. DDD is common and causes no symptoms in many older individuals. Everyone over about the age of 50 has some degree of DDD, which may or may not be symptomatic and functionally limiting. Osteoarthritis of the spine is frequently accompanied by DDD, while DDD without associated OA is also common. DDD can be seen on X-rays, MRI, and CT scans of the spine. It appears as narrowing of the space between vertebral bodies. Symptomatic DDD occurs between the 5th lumbar vertebra and the 1st sacral vertebra (L5-S1).

Sometimes a combination of OA and DDD produces enough symptoms that surgical fusion is performed in the lumbar spine (lumbar fusion) or cervical spine (neck). This procedure is done in an attempt to stabilize the spine and decrease pain. The surgery requires taking strips of bone from the posterior (back) upper part of the pelvic bone and laying them over the vertebral bodies that need to be stabilized (see Figure 4 below). Bone is living tissue and will incorporate the vertebral bodies into one solid mass. Sometimes, the bone strips do not incorporate well and the surgical fusion partially or wholly fails. Some fusions involve only two vertebrae, but multiple vertebrae may also be fused.

figure 4

http://www.jamesdisabilitylaw.com/back-injuries.htm#Degenerative_Disc_Disease_(DDD)

http://www.google.com.eg/imgres?imgurl=http://wiki.cns.org/wiki/images/0/03/Degenerative_disc_disease.jpg&imgrefurl=http://wiki.cns.org/wiki/index.php/Degenerative_Disc_Disease&usg=__fc681vAyEjRSyV3xOL2_RWtQVJA=&h=384&w=250&sz=23&hl=en&start=2&sig2=eNZJ3d6V4k_7UAPLw7BM4Q&itbs=1&tbnid=nCqP2wdJCQgcsM:&tbnh=123&tbnw=80&prev=/images%3Fq%3Ddegenerative%2Bdisc%2Bdisease%26hl%3Den%26gbv%3D2%26tbs%3Disch:1&ei=xB8QTJPAGYuu4QbgjLnzDA