Primum non nocere: First do no harm, the concept of nonmaleficence, holds true today more than ever before with the rapid technologic innovations in the field of spine surgery. It has become prudent to debate the use of an intervention that may carry a greater risk of harm than the presumed benefit. There is no such thing as a simple spine operation. The definition of the term complication in the spine literature and in the literature of the federal agencies is inconsistent. A complication is defined as any clinical episode that may affect patient outcome or that may require intervention, further diagnostic tests, or monitoring. Added to this immediate complication are any long-term complications that develop long after the actual surgical procedure.
The prospective studies have shown higher rates of complications in spine surgeries than the retrospective studies. In a review of 79,471 patients with 13,067 reported complications, the overall complication incidence was estimated to be 16.4% per patient. It has been estimated that about 10% to 20% of patients undergoing spinal surgery may develop complications. The overall complication incidence was highest for thoracolumbar surgery (17.8%) and for cervical spinal surgery (8.9%). A study of 3475 patients from the database of the National Surgical Quality Improvement Program found a complication rate of 7.6% and a mortality rate of 0.3%. A study based on the Scoliosis Research Society Morbidity and Mortality’s database of 22,857 patients, which includes 9409 cases of degenerative spine disorders, found a complication rate of 8.4%; the researchers also found that the patients with higher American Society of Anesthesiologists (ASA) grades undergoing spinal surgery had significantly higher rates of morbidity than those with lower ASA grades. Increased patient age and contaminated or infected wounds were identified as independent predictors of mortality. Increased patient age, cardiac disease, preoperative neurologic abnormalities, prior wound infection, corticosteroid usage, history of sepsis, ASA classification of >2, and prolonged operative times were found to be independently associated with increased risk of complications. In a large study by Hamilton et al., 108,419 spinal surgery patients were examined, and a 1.0% rate of new neurologic deficit was found in 1064 patients. Revision cases had a higher rate of deficits compared with primary cases. The pediatric cases had a higher rate of complications compared with the adult cases. The rate of new neurologic deficits for cases with implants was more than twice that for cases without implants.
The complications during general and degenerative spine surgeries can be classified into general and specific causes. The general causes include infection, bleeding, deep vein thrombosis, pulmonary embolism, chest and urinary infection, complications related to positioning, wound hematoma, and bleeding and infection. The other complications are specific to the anatomic site and procedure used.
Dural tears are a familiar complication in spine surgery. Incidental dural tears have a wide range of clinical sequelae and are not always benign. Patients with incidental dural tears incur a longer hospital stay and greater incidence of perioperative complications. The dural tears are an underreported adverse effect of spine surgery. A review of spine surgery cases has revealed that cerebrospinal fluid leaks after spinal surgery cost the US healthcare system an average incremental cost per patient of $6479 due to increased number of hospital stays, increased duration of hospital stays, and pharmacy costs. The incidence of incidental dural tears in spine surgery is estimated to be between 1% and 17.4% and is almost doubled in the revision cases (15.9%). The problem of adjacent segment disease and pseudarthrosis after spinal fusion is unlikely to decline in the near future. The causation of adjacent level disease is still not clear. It has been widely debated as to whether the adjacent segment disease is a progression of the degenerative process or induced by the fusion process. The adjacent segment disease is found to have an incidence of 2.9% per year in the first 10 years after the cervical fusion. It has been estimated that 25.6% of patients who had anterior arthrodesis would have adjacent level disease within 10 years of the operation. A large review of lumbar surgeries has shown that about 23.6% of revision surgeries are done for pseudarthrosis. Many risk factors have been found to be responsible for pseudarthrosis, such as smoking; osteoporosis; use of steroids, nonsteroidal antiinflammatory drugs, and antimetabolites; and use of allograft versus autograft. The incidence of kyphosis after cervical laminectomy is estimated to be 20%. The loss of posterior support leads to gradual development of kyphosis. This leads to constant contraction of extensor muscles, causing fatigue and neck pain. Multilevel laminectomies are best avoided in younger patients.
Neurologic deterioration is the most feared consequence of any spine surgery. Acute neurologic deterioration due to postoperative epidural hematomas and compression from grafts and hardware needs to be addressed urgently and reexplored. Neurophysiologic monitoring during spinal surgery and use of navigational tools are essential to reduce the incidence of neurologic deterioration. Also to be considered is any comorbid medical illness that the patient may be having, which can give rise to spinal cord ischemia and neurologic deterioration. Injury to the vertebral artery is an uncommon yet feared complication of cervical spine surgery. The overall incidence of vertebral artery injury in cervical spine surgery is 0.14% to 1.4%. The risk in instrumented posterior upper cervical surgeries is more than that involved in anterior subaxial spine surgery. The lateral dissection puts the vertebral artery under risk, and orientation of midline needs to be kept in mind throughout the surgery. The risk in instrumented posterior upper cervical surgeries (4%–8% incidence) is higher than that in anterior subaxial spine surgery (0.3%–0.5%). Preoperative assessment of the course of the vertebral artery and the status of collateral circulation is important. The patient outcomes of vertebral artery injury can range from being clinically asymptomatic to experiencing infarcts, pseudoaneurysms, quadriparesis, sometimes coma, and even death. The bleeding can be managed by tamponade, hemostatic agents, and blood transfusion. If repair is not possible and contralateral circulation is deemed adequate, endovascular coiling or primary ligation needs to be done. Fortunately, 90% of vertebral artery injuries do not result in any permanent harm. Only 10% of cases end up with permanent neurologic injury. Postinjury angiogram has to be done to rule out pseudoaneurysm or arteriovenous fistula formation. The use of intraoperative neuronavigation and a micro-Doppler probe is helpful to prevent this complication.
Complications due to instrumentation can be avoided by careful perioperative workup. Cervical plate loosening is not a rare complication. Osteoporosis, multilevel fusion, long lever arm imposed by the plate, and close proximity of screws to disc space are known to predispose the plate to loosening. About two-thirds of loosening was associated with nonunions. Multilevel cervical fusions have increased the complication rate of instrumentation failure and may need to be supplemented by posterior fusion. Most hardware failures are not symptomatic and can be treated conservatively. Cervical lateral mass screws are associated with nerve root impingement by the screws. If the sagittal angulation is less than 15 degrees, there is a risk of nerve root impingement by the screws. Exposure of the lumbar spine anteriorly can be associated with vascular injuries, with an incidence ranging from less than 1% to 15%. Most injuries occur because of incorrect vessel dissection or identification, or lack of surgical control. Venous lacerations are controlled by suture repair. Arterial injuries can have late presentation due to vessel thrombosis.
Minimally invasive spine surgery is gaining popularity, but with every new technique there is an associated learning curve. There is also the increased radiation exposure that is associated with doing minimally invasive procedures. The limited tactile feedback, the steep learning curve, the difficulty of depth perception, and the degree of manual dexterity required are the factors that one needs to keep in mind during minimally invasive spine surgery. Postoperative C5 palsy has an incidence of 3.4% after cervical laminectomy. The C5 root has a short and direct course of exit and is subjected to traction with posterior displacement of the spinal cord after laminectomy. Recovery may vary from weeks to several months. The use of bone morphogenic protein in spine surgery has been shown to be associated with dysphagia, hematomas, seromas, osteolysis, increased neurologic deficits, and even cancer.
This constantly evolving medical science is as yet imperfect, and complications will continue to occur. But it is important that the science of “complications” is understood and that a methodology is worked up to find solutions for these complications. The following chapters will address the complications that arise in general and degenerative spine surgery.