Multilevel Fusion Risks

The addition of multiple levels in a spinal fusion surgery increases the complexity of the procedure and may also increase the risk of adverse events or complications compared to single-level fusion surgery.

Immediate surgical risks

Immediate surgical risks include adverse events, which typically occur immediately after the surgery but may also occur over time. Research indicates that around 24% to 35% of patients may need revision surgery due to an adverse event or complication.^,

• Multilevel procedures take longer than single-level fusions, and potential problems with blood loss, blood clotting, and post-surgical wound infections are directly related to the length of surgery.^, The risk of blood loss also increases with obesity, advanced age, and the number of fused levels.^, 
• The potential for nerve and spinal cord damage is a concern with any type of spinal surgery. Fusion surgeries approached from the back, such as posterior lumbar interbody fusion (PLIF), have a higher rate of neurological damage compared to surgeries approached from the front, such as anterior lumbar interbody fusion (ALIF).
• Serious neurologic conditions, such as cauda equina syndrome and injury to the spinal nerves, are the reported neurological complications of lumbar fusion surgeries. The risk of neurological complications increases with advanced age and is typically higher in women. Tear of the dural membrane, which surrounds the spinal nerves and holds the spinal fluid, is also fairly common with multilevel fusion surgeries including decompression. This condition is called durotomy and occurs in up to 20% of spine fusion and/or decompression surgeries.

In general, factors such as advanced age (over 70 years), underlying health conditions, and pre-existing problems in the spinal discs or joints with prior surgery increase the likelihood of developing complications after multilevel fusion surgery.^,

Late surgical risks

Potential risks and complications that may arise over time as healing takes place include:

• Loss of adjacent stability. It is common for surgeons to decompress a spinal level above or below a fused segment. Decompression is a surgical procedure that is performed to alleviate pain caused by pinched spinal nerves. During a lumbar decompression back surgery, a small portion of the bone over the nerve root and/or disc material from under the nerve root is removed to give the nerve root more space and provide a better healing environment.
  When decompression is performed above a fused segment, the integrity of the strong spinal ligaments, which act as tough bands to support and stabilize the spine (especially while bending forward), can be compromised due to excision, eventually leading to segmental instability in the region. 
• Fusion failure. Multilevel fusions containing 3 or more levels have a significantly higher risk of developing pseudoarthrosis (failure to achieve proper bony fusion). Failed fusions also result in loss of function and increased usage of pain medication. Fusion failure is typically more common in the L5-S1 spinal segment, occurring in up to 24% of multilevel surgeries that involve this segment. 
  Specific factors that contribute to pseudoarthrosis include diabetes, obesity, osteoporosis, tobacco use, and advanced age.

  See Failed Spinal Fusion Surgery

• Implant failure. Implant failure (loosening or breakage of the screw or rod) may be associated with fusion failure and a poor clinical outcome. In the lower back, common implant-related problems include pedicle screw loosening, especially of the screws at S1, and infection. Some patients with pedicle screw loosening may develop back pain and need revision surgery to fix/remove the hardware. 

• Adjacent segment disease. Mobile spinal levels surrounding the fused segments bear additional stresses as motion is restricted across the fusion. This additional stress is felt to contribute to a higher incidence of degeneration of adjacent segments, which could result in symptoms and the need for additional surgery in the future. This condition is known as adjacent segment disease. The stress seen by an adjacent level and the risk of adjacent segment disease is felt to be progressively higher with more levels stiffened by fusion. Therefore, it is thought that multilevel spinal fusions may have a higher risk of adjacent segment disease than single-level fusions. 

Specific factors that contribute to adjacent segment disease include advanced age, obesity, pre-existing degeneration of the discs of the adjacent segment, and menopause. Research indicates that at least 30% of patients with lumbar spinal fusion may develop adjacent segment disease over time. 

These complications ultimately result in failed back surgery syndrome—a generalized term that is used to describe the situation when the outcome of back surgery does not correspond with the expected results of the surgeon and the patient. 

It is advisable for patients to talk to their surgeons in detail and understand the type of spine surgery, including its potential benefits, risks, and surgical alternatives before scheduling the procedure. Taking necessary precautions and following activity restrictions as instructed during the recovery period can help heal the surgical site and prevent future complications.