In a typical back surgery that involves the removal of the diseased intervertebral disc (discectomy), it is followed by the fusion of the two vertebral bones that were previously separated by that disc. These discs are designed to become joined and permanently fused with one another. To facilitate this permanent fusion into one spinal bone, metal hardware is used to hold the two bones together, or a bone graft is implanted, from bone materials taken from the pelvis or femur. If the procedure is successful, a permanent organic fusion between the two bones will occur, stabilizing that level of the spine. Pseudarthrosis is a condition when the discs don't fully fuse together and instability in that disc space.
When a back surgery that involves the removal of an entire disc and a spinal fusion occur, it may take some time before doctors and patients know that the surgery was successful. The bone graft is an inexact science and the two bones don't fully merge overnight. It make take up to a year before two or more merged vertebral bones achieve complete fusion and stability, and the nerves that were compressed retain their previously level of functioning - if ever. Doctors and their patient's don't go into any type of surgery lightly, particularly one such as a spinal fusion, which are associated with some of the longest recovery times - even compared to most other surgeries. On the other hand, when degenerative conditions such as degenerative disc disease affect the nerve roots to the point where the nerves become damaged and the muscles that support the back atrophy, something must be done. When the nerves and muscles are seriously affected, then the removal of the disc and a fusion of the adjacent bones will be performed to try to stop or reverse the damage.
As the vertebral bones are fusing, the nerves and spinal muscles may begin on their recovery. This recovery may proceed at a slow or rapid pace, and you may never recover to the full strength and sensation that you had before. A successful fusion of the vertebral bones will make it more likely that you will recover from the nerve compression and conditioning of spinal muscles.
Spinal Fusion. As stated above, a spinal fusion is performed to stabilize the portion of the spine where one or more degenerative disc were causing compression of the spinal nerve roots. A fusion may also be performed to stabilize a part of the spine that was causing the spine to have an abnormal curvature or motion at a vertebral segment. Motion as the vertebral segment may cause damage to the other soft tissues near that level of the spine, a straining of the ligaments, back pain, and inflammation. If the procedure is successful, the bones will fully merge, and pseudarthrosis will not occur.
Procedure. The procedure is designed to limit motion segments of the spine that are too unstable. A motion segment is defined is two vertebral bones connected by an intervertebral disc and bilateral facet joints. In a spinal fusion surgery more than one motion segment may be fused, depending on how many unstable segments there are. A bone graft will be inserted between the surfaces of the vertebral bones that will come in contact with one another. Typically the bone will be taken from the patient's own hip (autograft bone), but in some cases bone material may be taken from a cadaver (allograft bone) or from a synthetic source (synthetic bone graft substitute).
Though the purpose of the procedure is to reduce motion of the spine, rather than other most orthopedic treatments that are designed to improve mobility, most patients don't experience hardly any movement limitation. Most patients experience little limitation as only one motion segment has been fused. Patients experience much more limitation of movement if there are fusions at more than one motion segments.