Evaluation and Management of Postoperative Wound Infections of the Anterior and Posterior Spine

CHAPTER PREVIEW

CHAPTER SYNOPSIS:

Infection is a serious complication of spinal surgery that may occur early or late in the postoperative course, although early presentation is much more common. Prevention is best, but when an infection does occur, it is important that detection is early so that aggressive treatment may be initiated to improve outcome. This chapter offers guidelines for the management of these postoperative spinal infections.

IMPORTANT POINTS:

Patient Factors That Increase Risk for Infection

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Chronic illness (e.g., diabetes mellitus)
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Advanced age
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Obesity
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Poor nutrition

Physician Factors That Increase Risk for Infection

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Presurgical site preparation (e.g., shaving)
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Operative time
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Sterile technique
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Use of operating microscope or loupe magnification

CLINICAL/SURGICAL PEARLS:

Early Signs and Symptoms of Infection

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Pain that is resistant to normal postoperative pain medications
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Excessive erythema around incision
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Persistent drainage especially in a previously dry wound
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Fever

Initial Laboratory Data

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Complete blood cell count (white blood cell count)
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Erythrocyte sedimentation rate (normally peaks 4–5 days after surgery and normalizes within 2 weeks)
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C-Reactive protein (normally peaks 2 days after surgery and normalizes within 5–14 days)

Imaging

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Magnetic resonance imaging
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Computed tomographic scan

Treatment

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Almost always warrants surgical incision and drainage unless very superficial (e.g., suture abscess)
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Targeted antibiotic treatment

CLINICAL/SURGICAL PITFALLS:

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A high index of suspicion for infection should be maintained with all patients at higher risk.
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In cases of cervical infection, a concern should always exist for the presence of esophageal perforation, which must be adequately ruled out.
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Surgical debridement in the presence of infection may need to be repeated after the initial “washout.”
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Most early infections can be eradicated while maintaining the hardware and bone graft; removal should be reserved for recalcitrant infections or considered in late infections.

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Despite advances in antibiotics and surgical technique, postoperative infection remains as a significant complication to spine surgery. The cost of postoperative infection in a lumbar fusion is estimated to be 4.7 times that of an uncomplicated procedure. The ultimate outcome of a surgical procedure can, in many instances, be salvaged if these infections are identified and treated appropriately. However, in some circumstances, the goal of management can be only to minimize the resultant morbidity. This chapter attempts to offer some guidelines to aid in the operative and nonoperative management of postoperative spine infections.

PREVENTION AND RISK FACTORS

Several factors may influence the rate of postoperative infections. Although some aspects may be readily modifiable (e.g., administration of prophylactic antibiotics, adherence to strict aseptic techniques), other factors are not as easily manipulated. For instance, both patient characteristics (e.g., diabetes, increasing age, obesity, poor nutrition) and physician particularities (e.g., presurgical shaving, operative times, use of an operating microscope or loupe magnification) can adversely affect outcomes. Some factors have been evaluated but did not demonstrate a correlation with postoperative infection. For example, Banco et al. evaluated the effect of level of training and found no correlation with resident or fellow involvement, and Carragee and Vittum found that allowing patients to shower 2 to 5 days after surgery did not increase infection rates. A greater understanding of how these patient and physician characteristics potentially influence infection risk will enable physicians to decrease the overall risk.

Preoperative Risk Factors

Patients who have multiple co-morbidities (i.e., greater American Society of Anesthesiologists scores) have poorer outcomes. Studies have shown that smoking, diabetes, obesity, and alcohol abuse are statistically significant preoperative risk factors. Therefore, patients should be counseled before surgery on the increased risk associated with these modifiable behaviors. Smoking, in particular, has been associated with a greater infection rate and diminished wound healing, but some discrepancy exists in the literature as to whether a preoperative smoking cessation program is effective in diminishing the rate of wound complications. Although many studies have found increased postoperative complications (including infection) in overweight/obese patients, other studies have not clearly found weight to influence outcomes. Recently, diabetes was shown to be the greatest independent risk factor for infection after spine surgery. Preoperative fasting glucose level greater than 125 mg/dl and a postoperative random serum glucose level greater than 200 mg/dl are also risk factors for development of infection after spine surgery. However, further research is necessary to determine whether strict serum glucose control actually decreases the incidence of surgical site infection in the patient with diabetes.

Preoperative and Intraoperative Risk Factors

Presurgical shaving has been shown to increase the risk for surgical-site infection in cranial surgery. Recently, a prospective, randomized clinical trial of presurgical shaving with a razor versus no shaving showed an increase in the postoperative infection rate in those who were shaved before surgery.

The administration of prophylactic antibiotics has led to a reduction of postoperative spine infection to less than 6%. Proper antibiotics should be administered and completed within 1 hour of surgery start time. The administration of an additional dose of antibiotic should be considered for cases that exceed 4 hours. This protocol has been shown to be effective in the prevention of surgical-site infection in lumbar spine surgery.

The use of a headlamp, loupes, or an operating microscope has been used by spine surgeons to aid in the visualization of the operative site; however, an increased risk for disc space infection after microsurgery versus open laminectomy/discectomy has been reported. In a simulated discectomy performed to quantify the bacterial shedding, both the headlamp with loupes and the microscope were found to cause increased bacterial shedding as compared with control cases.

Gruenberg et al. suggest that the use of ultraclean air technology can decrease infection rates in complex spine procedures. Paying attention to hemostasis to minimize postoperative transfusions may be beneficial because postoperative transfusion has been associated with increased infection, although this issue can be complex in that transfusion is more likely in more prolonged or complicated cases. Other important factors under the control of the surgeon are limiting the amount of operating room traffic, operating efficiently, and ensuring that all personnel involved with the handling of instruments and implants follow strict aseptic technique.

DIAGNOSIS

Despite advances in diagnostic imaging and laboratory tests, the most important resource for the identification of spinal infections remains a high index of suspicion. Most spine wounds should dry within 3 to 4 days; drainage beyond that time frame should make one wary of either a postoperative hematoma (placing the patient at risk for subsequent infection) or potentially an already present infection. In the weeks that follow, some of the classic signs of wound infection may be present, such as erythema, warmth, and fever. However, the wound can also be well healed and appear clinically benign, but the patient may describe pain that appears excessive. Pain out of proportion in the postoperative spine patient can be difficult to judge because of the preponderance of preexisting psychosocial and underlying pain issues in spine surgery patients. Finally, if a spine wound is dry for several days and then begins to drain, this almost always represents an infection and should be treated aggressively.

Advances in spinal instrumentation and anesthesia, coupled with data showing the efficacy of a limited course of postoperative antibiotics, have drastically shortened the average postoperative stay of patients who underwent spine surgery. Shorter lengths of stay have led to greater than half of all surgical-site infection diagnoses by postdischarge surveillance. Because of this, it is important to ensure that patients are aware of the signs and symptoms of infection, and that they are instructed to contact the surgeon should they experience these problems.

The most common laboratory data used are white blood cell count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP). ESR levels typically peak 4 to 5 days after surgery, whereas CRP levels generally peak after 2 only days ( Fig. 38-1 ). In cases where the diagnosis is uncertain, serial laboratory testing can be performed over several days to look for trends in the ESR and CRP level.

The radiologic imaging modality of choice continues to be magnetic resonance imaging (MRI) with gadolinium. In postoperative discitis, plain radiographs may demonstrate demineralization, decreased disc space height, and end plate bone destruction, but these changes are not seen until 4 to 6 weeks after surgery. Computed tomography (CT) scanning has also been found to be unreliable in the early stages of infection. Radionuclide imaging may give false-negative results, and even if positive, it is nonspecific for postoperative discitis.

The most reliable MRI findings in postoperative spondylodiscitis are decreased signal intensity of the adjacent vertebral bone marrow in T1-weighted imaging with gadolinium. Other findings include increased signal intensity of the disc space and vertebral end plates on T2 imaging. Because the early postoperative MRI changes are difficult to distinguish from infection, one should rely more on the clinical judgment and laboratory data to make a diagnosis ( Fig. 38-2 ). If a neurologic deficit is present, then an MRI would be warranted to evaluate for the presence of and location of an epidural abscess. If the infection presents in a more subacute or late time frame, it becomes important to evaluate for the possible presence of any perispinal abscesses that would need to be addressed at the time of debridement ( Fig. 38-3 ). CT may, at times, be enough to assess for fluid collections and offers additional information regarding placement status of hardware and healing of the fusion mass ( Fig. 38-4 ).