Complications of Lumbar Spine Fusion Surgery

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Chapter 8 Complications of Lumbar Spine Fusion Surgery

Justin S. Field

Chapter Overview

Chapter Synopsis: Lumbar spinal fusion surgery may be used as a treatment for chronic back pain that arises from lumbar spinal stenosis when physical and drug therapies have failed. This invasive surgery carries particular risks that should be well understood by the treating physicians. Infection, dural tears, pseudoarthrosis, and adjacent segment degeneration are the most common complications, but more serious consequences can also arise, including root injury, paralysis, and death.

Important Points:

Many patients have back and leg pain arising from lumbar spinal stenosis with or without instability.

Conservative treatment in the form of physical therapy, chiropractic care, medications, and injections should be the first line of care. However, when conservative modalities fail and there is obvious instability or potential for instability, as well as acute neurologic changes, spinal surgery must be considered.

Lumbar surgery often includes decompression of the soft and bony tissues contributing to central and neuroforaminal stenosis that may be compressing the spinal cord or nerve roots. This can reliably relieve pain, numbness, and weakness.

It is crucial to understand the specific complications related to lumbar spinal fusion and to recognize and treat them immediately if they occur.

The most commonly discussed complications directly related to lumbar spinal fusion include infection, dural tears, pseudoarthrosis, and adjacent segment degeneration.

Rarer, more serious complications associated with lumbar spinal fusion include nerve root injury, paralysis, massive blood loss, blindness, heart attack, stroke, and death.

Careful patient selection, meticulous surgical technique, expert intraoperative anesthetic monitoring and care, and extensive postoperative monitoring can significantly decrease many of these complications.

Emerging surgical techniques and refinement of equipment have been directed at reducing these complications, but quality evidence is still needed to prove their efficacy.

Introduction

Back pain affects millions of people and is one of the most common reasons why patients consult with a medical professional. Many of these patients have back and or leg pain because of lumbar spinal stenosis with or without instability. Conservative treatment in the form of physical therapy, chiropractic care, medications, and injections should be the first line of care if a patient does not present with new neurologic insult. If these conservative modalities fail, then surgery must be considered.

Most lumbar spine surgery involves decompressing the soft tissue, which often includes a herniated disc (Fig. 8-1) or hypertrophied ligamentum flavum. Lumbar spine surgery also involves decompressing the bony elements, which can include hypertrophied facet joints, spinous processes, and lamina that make up the spinal canal. By decompressing both soft and bony tissue, spine surgery can often make patent both central and neuroforaminal narrowing that may be impinging on the spinal cord or nerve roots. Thoroughly decompressing the stenosis and nerve roots can reliably relieve leg pain and its associated symptoms of numbness and weakness. However, there are instances wherein there is obvious instability, spinal spondylolisthesis (Fig. 8-2), or the potential for instability. In this situation, a surgeon must consider both decompressing the stenosis along with stabilizing the affected spinal segments.

Fig. 8-1 Large herniated L4–L5 lumbar disc requiring decompressive surgery.

Fig. 8-2 Significant L5–S1 spondylolisthesis requiring surgery.

Particular ways to achieve fusion of the lumbar spine are discussed throughout the literature. Spinal fusion is a very successful procedure when chosen for patients with the correct indications for surgery. Newer surgical technologies and minimally invasive surgery have been touted to result in quicker recovery and less morbidity for the patient. However, lumbar spinal surgery and fusion with any approach has its associated relevant complications.

Some very serious complications of lumbar spine fusion have been reported, including nerve root injury, paralysis, massive blood loss, blindness, heart attack, stroke, and death. A comprehensive preoperative workup can help to stratify those patients at the most risk for medical complications. In some instances, optimization of a patient’s preexisting medical conditions (e.g., untreated diabetes, hypertension, reactive airway disease) should be taken to minimize their risks before surgery. Expert intraoperative anesthetic monitoring and care, as well as postoperative monitoring, can significantly decrease many of these complications. The surgeon must work effectively and efficiently to address the patient’s disease but also keep operative time as low as possible. Increased operative time often leads to increased complications, including increased blood loss, infection, and possibly blindness from being prone for too long (>8 hours).

The most commonly discussed complications directly related to lumbar spinal fusion include infections, dural tears, pseudoarthrosis, and adjacent segment degeneration (ASD). These specific complications are all important to understand, and if they occur, they must be recognized and treated rapidly, and as such will be elaborated on in more depth.

Selected Complications

Infection

Patients undergoing lumbar spinal fusion typically receive prophylactic intravenous (IV) antibiotics within 1 hour of surgery and postoperatively in several doses. This perioperative regimen, along with proper intraoperative sterility, has decreased infection rates dramatically. However, postoperative spinal wound infection is not an uncommon complication (Fig. 8-3). If not properly recognized and treated, a wound infection can be devastating and affect the ultimate desired surgical outcome.

Fig. 8-3 Normal postsurgical fusion (A) compared with postsurgical infection (B).

A review of the literature shows that postoperative wound infections are common and range from 1% to 6% after lumbar spine fusions.¹ Staphylococcus aureus was the most common pathogen cultured, but some patients have multiple organisms causing an infection. Multiple studies have assessed risk factors for postoperative wound infections (Table 8-1).

Table 8-1 Patient and Surgical Risk Factors for Postoperative Wound Infections

Patient Risk Factors for Postoperative Wound Infections	Surgical Risk Factors for Postoperative Wound Infections
>60 years of age	Complex spine procedures
Smoking	Fusing multiple levels
Diabetes	Spinal revisions
History of previous surgical infections	Anterior or posterior reconstruction
Obesity and increased body mass index	Increased operative times
Alcohol abuse

Age greater than 60 years, smoking, diabetes, previous surgical infection, increased body mass index, and alcohol abuse were statistically significant risk factors. In addition to these factors, more complex spine procedures that involved multiple levels being fused, tumors, surgical revisions, and anterior or posterior reconstructions, also increased the rates of postoperative infections and complications.²

Early detection is of paramount importance for appropriate care of any postoperative infection. Patients with postoperative infection may complain of classic symptoms, including fever, chills, nausea or vomiting, erythema, and drainage from the incision. Patients also may have more insidious complaints such as an increase in pain after an initial improvement postsurgically. If an infection is suspected, it is important to have the patient urgently come to the clinic or a nearby hospital for immediate evaluation. Thankfully, suspected infection is often the result of much less serious superficial wound dehiscence. This can usually be treated with dressing changes and oral antibiotics as needed. When treating wound dehiscence, it is imperative to have the patient follow up closely for several evaluations to ensure the wound is healing appropriately. If the patient remains symptomatic and the incision is not healing, then further workup, including imaging in the form of magnetic resonance imaging (MRI) or computed tomography (CT), is warranted. This may show a postoperative abscess, seroma (fluid collection), hematoma, or even an undetected cerebrospinal fluid (CSF) leak.

If a wound infection is diagnosed after a spinal fusion, aggressive treatment is essential. Many physicians also obtain an infections blood workup, including complete blood count, erythrocyte sedimentation rate, C-reactive protein test, and blood cultures with sensitivities. MRI or CT scans with and without contrast are sometimes obtained to evaluate the underlying pathology. Suspected deep tissue infections require deep wound irrigation and debridement. At the same time, targeted wound cultures and sensitivities must be taken and sent to pathology for further analysis. Wound irrigation and debridement may be required multiple times before closure of the wound is possible.

When one has a deep infection, there is much debate on whether instrumentation needs to be removed at the time of irrigation and debridement. Instrumentation is a foreign body and thus can be a nidus for infection because bacteria can form a glycocalyx, or an extracellular adhesive slime. This bacteria-generated layer can make it difficult or impossible for antibiotics to penetrate the bacteria and rid the area of infection. If the infection is of late onset, there may be evidence of full bony fusion. In that instance, hardware may be removed. However, with earlier infection, the hardware may need to remain in place to maintain structural stability of the lumbar spine. Aggressive debridement of soft tissue, bone, and surgical hardware is obviously needed in that circumstance. In all instances of wound infection, it is important to consult a patient’s primary care physician as well as infectious disease specialists. Typically, an infection requires 4 to 8 weeks of IV antibiotics through a peripherally inserted central catheter line with the choice of antibiotics chosen by an infectious disease specialist and dependent on the results of the cultures and sensitivities of the organism.

Dural Tear

Most lumbar spine fusion cases involve decompression of posterior elements. The soft tissue is often decompressed, which can include a herniated or extruded disc, excessive fat, or hypertrophied ligamentum flavum. Lumbar spine surgery also involves decompressing the bony elements, which often include hypertrophied facet joints, spinous processes, and lamina. The neural elements bathe in CSF and are contained within a thin tissue, the dura mater, before branching out into the neuroforamen to supply motor and sensory function to the body. The dural sac with its neural elements is compressed in central spinal stenosis. There exist central, lateral recess, and foraminal stenoses, and patients may have one or all three of these components comprising their stenosis. To adequately decompress the canal and ligamentum flavum, often the medial aspect of hypertrophied facets joints are excised. In the process of accomplishing this, dural tears may occur secondary to the bone and soft tissue being adherent to the dura from longer standing stenosis or a large herniated disc (Fig. 8-4). While performing a posterior decompression of the lumbar spinal canal, bony spicules may also pierce the dural sac, causing CSF leaks. As a rule, the more severe the spinal stenosis, the higher the likelihood of a dural tear occurring as a result of surgery. In addition, patients who have had previous lumbar spine surgery and have recurrent stenosis also have an increased risk of a dural tear because of formation and adherence of scar tissue.

Fig. 8-4 Dural tear occurring after medial aspect of hypertrophied facets joints are excised.

Dural tears are a common complication of lumbar spine surgery (Fig. 8-5). Khan et al³ reviewed a total of 3183 degenerative lumbar spine cases at one institution, and cases complicated by dural tears were identified. They found that the incidence of dural tears during a primary lumbar surgery was 7.6%. This was significant but appreciably lower than the 15.9% dural tear risk seen with the surgical revision cases. Cammisa et al⁴ reviewed a total of 2144 patients and found that dural tears occurred in 3.1% of patients during spinal surgery. The incidence of dural tears varied according to the specific procedure performed but was again highest in the group that underwent revision surgery.

Fig. 8-5 Large dural tear.

(From Pereira Filho Ade A, et al: Symptomatic thoracic spinal cord compression caused by postsurgical pseudomeningocele. Arq Neuropsiquiatr 65[2-A]:279-282, 2007.)

The treatment for dural tears occurring intraoperatively is direct repair of the dura with a thin silk or Prolene suture that nicely approximates the dura tissue edges to each other without impinging the neural elements. Wang et al ⁵ describe primary repair followed by short-term bed rest. This protocol led to no long-term deleterious effects or increased rates of infection, neural damage, or arachnoiditis. In addition, closed suction wound drainage does not aggravate the leak and can safely be used in the presence of a dural repair.

There are situations, however, when it may be difficult to repair a dural tear. In these cases, a thin collagen sponge can be placed over the dural leak as well as covering the rest of the exposed dura. In addition, several products can form a superficial seal over this area in conjunction with the sponge to seal off the leak. It is important to have the patient lie flat in bed for at least 48 hours after this scenario. Then the patient may gradually increase the inclination of the bed and can ambulate as long as symptoms indicative of a dural leak (e.g., headache, nausea, dizziness) do not occur.

For patients who have continued dural leakage of CSF, other options are available as well. Kitchel et al ⁶ describe the effectiveness and safety of a temporary subarachnoid shunt placed in the upper lumbar spine that is removed after 4 days. These patients must be monitored very carefully. Many of these authors’ patients were treated successfully in this manner with resolution of CSF drainage and symptoms and no permanent sequelae. An undetected postoperative CSF leak or cases with persistent drainage are more commonly treated with reoperation, identification, and repair of the dural leak.

Pseudoarthrosis

Lumbar spine fusion has become a widely used procedure, being performed increasingly over the past 2 decades. Initially, the surgery was only indicated for Potts disease, severe spinal deformity, unstable spine trauma, and tumor excisions leading to instability. The current indications for lumbar spine fusion have broadened and include any spinal instability and painful degenerative disc disease in carefully selected patients. Methods to achieve fusion have evolved and include new instrumentation devices, various biologics, and different approaches. A surgeon can now perform an anterior lumbar interbody fusion or posterior lumbar fusions from midline to true lateral. The lateral approach involves accessing the retroperitoneal space and traversing carefully through the psoas muscle to enter the disc space. Even though technology and biologics to achieve fusion have improved, pseudoarthrosis may still occur. Pseudoarthrosis is defined as an incomplete spinal fusion when a fusion is attempted. A large prospective review of revision surgeries revealed that 23.6% of these revision fusion surgeries were performed for pseudoarthrosis.⁷ However, this may underestimate the true incidence of pseudoarthrosis because many patients remain asymptomatic despite the lack of a complete fusion.

Pseudoarthrosis is essentially a failed attempt at spinal fusion. Typically it manifests longer than 6 months after a spinal fusion procedure and presents with continued back pain and even recurrent radicular pain. The diagnosis is based on the clinical presentation and updated imaging studies. A pseudoarthrosis should be suspected when a patient has persistent complaints that are not relieved with physical therapy and other modalities. Flexion and extension radiographs show a continued degree of motion at the fused levels despite the instrumentation present. In addition, lucency may be seen around the pedicle screw instrumentation on the radiographs. A more precise radiographic tool to assess fusion is a thin-cut CT scan. CT scans more reliably assess fusion masses posterolaterally as well as in the interbody area.

Risk factors for nonunion include metabolic abnormalities, smoking, infection, and excessive motion at the fusion site (Box 8-1). Several studies have shown that not using instrumentation leads to increased pseudoarthrosis as well (Figs. 8-6 and 8-7). Fischgrund et al⁸ published the results of a prospective, randomized trial comparing decompression and posterolateral fusion with and without instrumentation in patients with degenerative spondylolisthesis and spinal stenosis. Average patient follow up was 2 years with the fusion rate significantly better with instrumentation than without (82% vs. 45%). However, they noted that good to excellent results occurred in both groups whether they fused or not. In 2004 Kornblum et al⁹ reviewed the noninstrumented fusion patients from the Fischgrund trial with 5 to 14 years of follow-up. They found that there was a significant difference between the long-term results of both groups. The pseudoarthrosis patients ended up having worse clinical outcomes with many of them requiring revision operations. Thus, evidence does support the use of posterior instrumentation (Fig. 8-8) to achieve higher fusion rates and better clinical outcomes.

Fig. 8-6 Fusion with bone graft only (no instrumentation) increases the risk for pseudoarthrosis.

Fig. 8-7 Fusion with bone graft only (no instrumentation) increases the risk for pseudoarthrosis.

Fig. 8-8 Fusion shown with bone graft and instrumentation.

Adjacent Segment Degeneration

After lumbar fusion is attained, an important question arises as to what the future holds at the adjacent levels that have not been operated on. It is unclear if lumbar ASD (Fig. 8-9) occurs as a result of lumbar spinal fusion or is part of a larger preexisting multifactorial disease process. Studies suggest an increase in risk for ASD in patients who underwent spinal fusion compared with patients who received nonfusion or no treatment. Annualized incidence rates for symptomatic ASD requiring reoperation from case series ranged from 0% to 3.9%. Approximately 26% of patients receiving lumbar fusion develop new lumbar ASD within the first 10 years after fusion based on one study.¹¹ The L3–L4 segment appears to be one of the most frequently involved levels, according to multiple studies. Because of this concern for ASD, many technologic advances have been made to decompress and stabilize the lumbar spine without rigid fusion. Some examples include the artificial disc replacement, pedicle-based motion-preserving devices, facet replacements, and interspinous implants. There has been much research done to validate the efficacy of many of these products. However, more time is needed to adequately assess the rates of ASD with these products versus that of lumbar spinal fusion.