Keywords

1 Definition

According to the surgical site and the time since surgery, postoperative spine infections can be divided into (a) superficial or deep and (b) acute (early-onset) or chronic (late-onset). It is also important to distinguish between infections occurring in adult and pediatric patients.

Superficial infections typically develop above the fascial layer and involve subcutaneous tissues and skin; on the other hand, deep infections do extend below the fascial layer (lumbodorsal fascia or ligamentum nuchae for posterior surgery and abdominal fascia or platysma for anterior surgery).

Acute infections are usually diagnosed within 3 to 4 weeks of the procedure, while chronic infections are diagnosed more than 4 weeks since surgery; for some authors, the cutoff between acute and chronic infection is 6 weeks. However, it is important to recognize the very late infection (sometimes years after the index procedure) usually secondary to low-grade pathogens such as Propionibacterium species and that can be cured by hardware removal.

2 Natural History

The incidence of postoperative spine infection is highly variable; it ranges from 0% to 18% depending on the type of surgery (surgeries without bone grafting or instrumentation have the lowest rate of infection) and of surgical approach (posterior cervical fusion > posterior lumbar surgery > anterior surgery).

Overall, the development of a postoperative infection put the patient at increased risk for pseudoarthrosis, chronic pain, adverse neurological sequelae, return to the operating room, worsened long-term outcomes, and – in most severe cases – even death.

3 Physical Examination

The typical physical signs of surgical site infection are pain, erythema, swelling of the incision or wound dehiscence, and purulent drainage from the wound; importantly, wound drainage for more than 1 week is a risk factor for deep infection. Other signs and symptoms are fever (present in about half of the patients), fatigue, and, in some cases, weight loss (depending on the chronicity of the infectious process).

Laboratory Tests: If surgical site infection is suspected, white blood count (WBC), erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) should be requested by the treating surgeon. However, used in isolation, WBC is a poor marker, and ESR is a nonspecific marker—though more sensitive than WBC—to rule out a surgical site infection. CRP is the most sensitive indicator currently available to diagnose postoperative infection. The combination of CRP and ESR values is the most predictive method for diagnosing and monitoring treatment response of postoperative spinal infections; however, no laboratory method has demonstrated excellent specificity/positive predictive value.

The use of procalcitonin (PCT) for the evaluation of spinal infection has shown lower sensitivity than CRP. Other relatively novel markers such as serum amyloid A (SAA) and presepsin, although promising, have limited clinical validation and require to be studied further.

4 Imaging

Plain radiographs are of limited use in postoperative spine infection although they should be obtained to assess for any hardware failure.

Computed tomography (CT) scan is the imaging of choice to evaluate bone, and it also provides information on soft tissue collections. Early bony changes include erosion and destructive changes at the level of the end plates and disk space narrowing. CT can identify (earlier than radiographs) lucencies around orthopedic implants.

Magnetic resonance imaging (MRI) with gadolinium contrast is considered to be the most sensitive modality for the assessment of postoperative infection. MRI findings usually associated with postoperative spine infection are rim-enhancing fluid collections, ascending epidural collections, evidence of bony destruction, and progressive marrow signal changes; the presence of hardware can create artifacts making the interpretation of the images more difficult.

Nuclear medicine (gallium-67 or technetium-99) can be used as an adjunct for the diagnosis of postoperative spine infection although it has limited sensitivity and is not used regularly in the diagnostic process.

5 Differential Diagnosis

Currently, the gold standard for the diagnosis of postoperative spine infection is a positive deep culture. Differential diagnosis focuses on the type of pathogen involved in the infectious process (Videos 66.7 and 66.8).

6 Treatment Options

Multiple debridement procedures of necrotic and infected tissue and long-term antibiotics are required for treatment. Exploring below the fascia is recommended for all but the most superficial infections. Bone graft that is loose at the time of debridement should be removed, but any graft material that is adherent to bony structures should be left in place; similarly, all necrotic, infected, and foreign material, such as sutures, must be completely debrided.

For early postoperative infection (acute or chronic <3 months), in cases where spinal instrumentation is present, the current recommendation is not to remove the hardware to avoid destabilizing the spine. For late postoperative infection (chronic >3 months), if fusion has occurred, hardware removal is usually needed to allow adequate debridement of the wound. The vacuum-assisted closure (VAC) system can be used in patients with acute infection; it has been shown to be a useful tool in the armamentarium of the spinal surgeon dealing with patients susceptible to deep postoperative infections, especially those with neuromuscular diseases (Fig. 66.1). VAC system is changed every 48 to 72 h.

Fig. 66.1
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Deep postoperative infection in a patient with spinal muscular atrophy. Use of VAC system. Hardware is left in place, and superficial and deep layers are progressively closed

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Equally important to multiple debridements and lavages is antibiotic therapy. Importantly, antibiotics should not be administered prior to culture results; if the patient is septic or unstable, antibiotics should be administered empirically to help prevent further clinical decline. Broad-spectrum antibiotics should be initiated prior to obtaining final culture results and adjusted depending on the results of the cultures. Although the duration of antibiotic therapy is controversial, short antibiotic course should be reserved only for patients without any hardware in place. For patients with deep infection and hardware in place, the length of antibiotic treatment is much longer, including 4 to 6 weeks of IV antibiotics followed by at least 4 to 6 weeks of oral antibiotics. Postoperative discitis/osteomyelitis is generally treated with >3 months of antibiotics depending on the inflammatory markers (Fig. 66.2).

Fig. 66.2
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Deep postoperative infection in a patient with severe deformity. Throughout debridement and lavage. Skin closure

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7 Expected Outcomes

A high index of suspicion is needed to make an early diagnosis; if treated promptly through debridement and lavage in association with targeted antibiotic therapy (according to deep culture results), the outcome is generally good. Older age, presence of comorbidities, smoking history, and obesity can be associated with poorer outcomes (Table 66.1).

Table 66.1 Risk factors
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8 Potential Complications

Potential complications are pseudoarthrosis, chronic pain, adverse neurological sequelae, return to the operating room, worsened long-term outcomes, and—in most severe cases—even death; in case of deformity surgery, the removal of hardware may cause the recurrence of the deformity (if fusion has not occurred).

9 What Should Patient and Family Know?

Before each surgery, patients and their families must be informed of the infectious risks, their treatment modality, and possibly short-, medium-, and long-term complications.