In most lumbar spinal operations decompression of the nerves of the spine is the main consideration because relieving the sensitive neural elements of the spine is what brings about benefits for the patient with reduced nerve pain (sciatica), improved function etc.
However, in patients with back pain as a significant symptom and particularly where there is instability, destruction or deformity to the mechanics of the spine fusion may be entertained to add strength to the spine by permanent immobilization of one or more of the spinal segments.
The idea is not new, and has been around for 70yrs, but probably is not indicated for patients with back pain from degenerative disc disease because simpler, less invasive treatments have been shown to be equally effective.
There remains a debate in the medical spinal world whether implants to add strength to the spine are a “safeguard or are superfluous” but I believe there is evidence in certain situations to support a lumbar fusion operation.
If you are suffering from a lot of back pain, and in particular have done for a long time, simple discectomy by removing disc material pressing on the nerves of the spine is unlikely to help you. If your disc prolapse is large and/or your MRI scan reveals marked degenerative features with loss of disc height, reactive changes or mal-alignment then is a significant chance the surgery may worsen your back pain. This is when a fusion operation may need to be considered.
A fusion operation necessitates the permanent linking together of the bones either side of a disc joint using implants to contain the bone graft (cages) and fixation screws (pedicle) and rods. A radical removal of all of the disc point allows bone to grow across the front of the spine (posterior inter-body fusion PLIF) or alternatively the degenerate disc joint is left alone and the bone graft laid on the back of the spine (posterior inter-transverse fusion).
The length of operation is 4-6hrs with often more blood loss and longer hospital stay than for a more simple discectomy operation. Minimally invasive fusion operations reduce this. However the operation is performed the risks of complications is increased with risk of nerve damage (weakness, numbness, paralysis of legs, bladder or sexual function) from infection, bleeding or misplaced implants and also increased risk of general complications from the longer anaesthetic time (vein thrombosis, pulmonary embolus, chest infection, heart attack, stroke etc).
Usually there is a good chance the longer operation will bring about benefit (60-80%) but there is no guarantee of this and even the chance that the fused segment could cause problems with adjacent segments in the future.
Swedish Spinal Stenosis Study (SSSS), Forsth et al
NEJM, April 2016
Spinal Patients Outcome Research Trial (SPORT), Weistein et al
NEJM, May 2007