The addition of multiple levels in the surgery increases the complexity of the procedure somewhat and also increases the risks compared to single-level fusion surgery. Potential problems with blood loss, arterial and venous thrombosis, and post-operative wound infections are directly related to the length of surgery, and multilevel procedures generally take longer than single-level fusions. However, the risks are not directly additive; a two-level fusion does not have twice the risk of a one-level fusion, but only a few percent increase in risk.
Preoperative considerations in multilevel fusion surgery relate to the larger size of the operative procedure. Consideration is usually given to preoperative blood donation, to have the patient's own blood available for transfusion if needed due to the higher blood loss commonly associated with multilevel procedures. One unit of donated blood may be all that is needed if expected blood loss is minimal, and up to 3 units may be recommended in some larger reconstructive procedures.
For larger anterior procedures and in high risk patients with a history of blood clots (deep venous thrombosis (DVT) or pulmonary embolus (PE)), use of a preoperatively placed removable filter into the Inferior Vena Cava (IVC filter) may be worth the added risk of the procedure in order to minimize the risk of a postoperative DVT or PE. These issues should be discussed with the treating surgeon as part of the preoperative discussion of surgical risk and ways to minimize these risks.
Longer term issues to consider in multilevel fusion surgery include the risk of failure of fusion (also known as nonunion or pseudoarthrosis), as well as the theoretically higher risk of adjacent level degeneration.
- Fusion failure of one or more levels in multilevel fusion surgery can occur in as high as 40 to 50 percent of cases, and is highly dependent on patient risk factors and the surgical technique used. Patient risk factors for fusion failure include being a smoker, history of osteoporosis, and history of prior fusion failure. Surgical techniques to enhance fusion rate include interbody and posterior combined fusion, use of patient's own iliac crest (pelvic) bone graft, and use of growth factors such as BMP-2 or OP-1. Again, the specific surgical technique used and risk of nonunion are subjects for the in-depth preoperative surgical discussion every surgical patient should have with his or her spine surgeon.
- Mobile spinal levels surrounding a spinal fusion see additional stresses when motion is restricted across the fusion. While it has not been proven, 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 is known as 'adjacent segment disease'. The stress seen by an adjacent level and risk of adjacent segment disease is felt to be progressively higher with more and 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.