Spinal fusion carries a number of risks, some general to any surgery and some specific to the procedure itself. Infection, blood clots, reactions to the anaesthetic, breathing problems, blood loss, cardiovascular issues, and muscle damage are all possible. Minimally invasive spine procedures will reduce the risk of most of these, as will ensuring a patient is in good general health prior surgery, is not obese, and does not smoke. The problems with circulation and collagen synthesis connected to smoking are most likely instrumental in the poor prognosis for smokers after any kind of surgery as concerns heart health. The most common cause of death after non-cardiac surgery, such as a procedure for spinal stenosis, is cardiac failure, with smokers particularly at risk (Faciszewski , 2001).
Risks specific to spine surgery
Surgery on the spine also carries the risk of accidental damage occurring to the spinal nerves, leading to weakness, pain, numbness, paraesthesia, incontinence, and paralysis. Surgeons may make use of somatosensory evoked potentials to monitor nerve signal transmission during surgery, although the effectiveness of SSEPs is questionable as the damage has usually been done before warning signs occur.
Risks of Infection
Superficial wound infection or deep infection of the vertebrae can occur and may require further surgery to remove infected material. The dura that covers the spinal canal may also be torn during surgery. This is rare and is usually noticed and repaired during the procedure. In a small number of cases the dura can leak spinal fluid and become infected, with the possibility of the infection spreading to the meninges and causing spinal meningitis. Preventative antibiotics may be given to patients before surgery and afterwards to reduce the risk of infection.
Stress on the Spine
Other risks of spinal fusion are associated with the restricted motion of the vertebrae at the levels fused. This can put extra stress on the remaining vertebra and discs and can cause degeneration in these tissues. This is referred to as adjacent level degeneration and may include fracture of the vertebra, necessitating further surgery. Slippage, or curvature, at other spinal levels is not prevented by spinal fusion surgery and may occur if the spine degenerates further. If more than one back surgery has been carried out, such as a discectomy or laminectomy, then the risk of subsequent problems is increased. Spinal disc replacements are being developed in an attempt to address some of the risks of spinal fusion.
Failed Back Surgery
It is possible that the segments do not form a successful fusion after surgery. This can be due to poor bone growth despite attempts to stimulate fusion. It may also be due to hardware failure, if a metal plate, screw, or cage has become loose after the procedure then the bone graft may not be held in the correct position to form an advantageous fusion. This may occur due to movement of the spine after surgery, or due to a fault in the hardware itself (this is rare). Graft rejection can also occur and is most common in cases where donor bone has been used. If an allograft is possible then this is always the preferred option as the patient’s body has a significantly lower risk of reacting against its own transplanted tissue.
Smoking Cigarettes and Cigars
Smokers have a particularly high risk of non-union after spinal fusion surgery. One of the reasons for this is that chemicals, such as nicotine, in cigarettes inhibits the formation of new bone. Brown (1986) found that smokers had a 40% chance of fusion failing to occur, in contrast to just 8% of non-smokers. Another study of patients having spinal fusion after an anterior cervical discectomy found that 50% of smokers failed to achieve a solid union compared to 20% of non-smokers (Goldberg, 2002).
A number of studies have demonstrated a link between nicotine and poor bone mineralization, along with reduced circulation, poor nutrient delivery, nutrient deficiencies, and inhibited growth of new bone. This alone is reason enough for surgeons to postpone such operations until a patient has successfully quit smoking and has minimal traces of nicotine in their system. Theiss (2000) showed that nicotine inhibits gene expression controlling both type I and type II collagen, bone morphogenic protein-2, -4, and -6, basic fibroblast growth factor (bFGF), and vascular endothelial growth factor (VEGF). This means that the growth of new bone cells and the blood vessels to supply them is seriously impaired when nicotine levels in the blood are raised. After surgery for spinal stenosis the body needs to be able to rapidly create new bone to fuse the vertebrae and restore some level of stability in the spine. Smoking is also detrimental to intervertebral disc health, and increases the amount of pain medication that patients use after surgery (Iwahashi, 2002, Krebs, 2010).
Minimally Invasive Fusion Risks
Minimally invasive spinal fusion using an approach through the abdomen has not proved as successful as traditional open fusion techniques. Often, the fusion has been unreliable, the operations have taken longer, and the procedure holds a higher risk of nerve injury. Many surgeons have either reverted to a traditional open procedure or used a posterior approach instead as this has been much more successful. Surgery times are actually shorter, with experienced surgeons, when using minimally invasive techniques and recovery times are also lessened. Patients experience less blood loss, and less trauma with this procedure which leads to less pain.
Controversy around spinal fusions
There remains some degree of controversy over the efficacy of spinal fusion for symptoms such as low back pain. A small number of studies have been carried out to establish the relative merits of such a procedure, but in most cases these studies are confounded by having no effective blinding of either patients or doctors. Many patients in non-surgical treatment groups cross over to the surgical group during such trials, reducing the power of the study’s results. In some cases it seems that spinal fusion surgery is little more effective than conservative therapy with cognitive behavioural therapy for treating chronic low back pain (Brox, 2003). Indeed, Brox found that the success rate was 70% after surgery and 76% after cognitive intervention and exercises with an early complication rate in the surgical group of 18%. Spinal fusion also has significantly more risk than conservative treatment and is more expensive. The Cochrane Review in 2005 concluded that instrumented spinal fusion appeared to have a higher success rate for fusion (although implants may obscure the imaging) but that clinical data varied significantly and more research needs conducting to enable appropriate treatment decisions to be made for patients with chronic back pain.