23.1 Introduction and Background

According to the Centers for Disease Control and Prevention, deep surgical site infection (SSI) is an “infection that appears to be related to the operative procedure and involves deep soft tissue (e.g., fascial and muscle layers of the incision).” ¹ In addition, it must have at least one characteristic listed in Table 23‑1. According to Aleissa et al, ² deep wound infection after spinal surgery is defined as “infection in which there is a direct communication between the infected materials and the spinal instrumentation and bone graft/fusion mass.” Deep SSI after spinal deformity surgery can be further classified as early or late infection. The definition of “late” SSI after spinal fusion is unclear. Two large studies of deep SSI after pediatric spinal deformity surgery defined early SSI as occurring less than 3 months after surgery and late SSI as occurring 3 months or more after surgery. ^{3 ,​ 4} As discussed later in this chapter, we used 3 months postoperatively as the cutoff between early and late infections.

Deep wound infection after pediatric scoliosis surgery is a devastating complication that typically requires prolonged surgical and medical management. These infections can compromise the outcome of deformity correction, especially in patients who require subsequent removal of implants. The other comorbidities and potentially life-threatening complications associated with spinal deep SSI include sepsis, vertebral osteomyelitis, neurologic compromise, and clinically important soft-tissue defects. ⁵ Deep SSIs also add substantial costs to treating patients. ⁶

The incidence of SSI after pediatric spinal deformity surgery varies by patient diagnosis. ⁷ The term “neuromuscular scoliosis” covers a wide variety of conditions, each with its own rate of infection associated with spinal deformity surgery. It is well established that infection rates are higher in patients with neuromuscular scoliosis compared with patients with adolescent idiopathic scoliosis. Table 23‑2 ^{5 ,​ 8 ,​ 9 ,​ 10 ,​ 11 ,​ 12 ,​ 13 ,​ 14 ,​ 15 ,​ 16 ,​ 17 ,​ 18 ,​ 19} summarizes the rate of deep SSI after pediatric scoliosis spinal surgery.

23.2 Risk Factors for Infection and Microbiological Data

Risk factors and microbiological data for patients with neuromuscular scoliosis who have developed deep SSI after spinal surgery are critical to understand, not only for prevention but also for formulating treatment plans. Surgical scoliosis correction is a major intervention in patients who typically have limited ability to adapt to imposed stress. Some of the factors that may account for the higher deep SSI rate in patients with neuromuscular scoliosis may be related to diminished or absent sensation in the lower body, lack of bowel or bladder control, previous spine surgery (e.g., myelomeningocele closure after birth), and altered soft-tissue coverage. Patients without sensation in the lower body are more prone to develop pressure sores and decubiti, which can lead to infection by either direct contamination or hematologic spread. Patients who lack bowel and bladder control are at risk of seeding a wound with feces or urine. Furthermore, these patients develop frequent urinary tract infections, which can spread to implanted instrumentation or a surgical wound. ³

Several studies have identified risk factors and bacteria associated with deep SSI after neuromuscular scoliosis corrective surgery. In a multicenter retrospective case control study, the degree of cognitive impairment was identified as a significant risk factor for deep SSI after scoliosis surgery in patients with cerebral palsy and myelodysplasia. ²⁰ Other risk factors identified in this study are listed in Table 23‑3. ²⁰ In the same study, 52% of the infections were polymicrobial. The most common organisms were coagulase-negative Staphylococcus, Enterobacter, Enterococcus, and Escherichia coli. ²⁰ In a multicenter study, Mackenzie et al ⁷ showed that nearly half of SSIs after scoliosis surgery contained at least one gram-negative organism. Significantly higher rates of gram-negative infections were found in patients with nonidiopathic scoliosis. In this study, Pseudomonas was the third most common organism after S. aureus and S. epidermidis. Aleissa et al ² reported that more virulent enteric and gram-negative organisms were more commonly isolated from early deep SSIs (e.g., Pseudomonas, Enterococcus), whereas low-virulence cutaneous organisms were more commonly cultured from late infections (e.g., Propionibacterium acnes, S. epidermidis). This is an important finding, especially when choosing antibiotic treatment for these infections.

Preoperative nutritional status and a positive urine culture have been evaluated as risk factors for deep SSI in patients with neuromuscular scoliosis. ^{20 ,​ 21 ,​ 22} It was previously reported that malnutrition may be associated with an increased rate of postoperative complications. ^{21 ,​ 22} In a multicenter study, Sponseller et al ²⁰ found that markers such as a preoperative albumin level below 3.5 mg/dL, a total lymphocyte count below 1,500 cells/mm³, and a hematocrit level of 33 g/L or less were not statistically correlated with increased risk of infection. ²⁰ Hatlen et al ²² showed that a positive preoperative urine culture was a significant independent risk factor for SSI after spinal fusion in patients with myelodysplasia.

The risk of deep SSI varies according to surgical approach and instrumentation type. It is higher after posterior spinal fusion, whereas infection after anterior spinal fusion is rare. ² Use of allograft bone has been identified as a significant risk factor for deep SSI after scoliosis surgery, particularly in patients with neuromuscular conditions. ^{2 ,​ 20} Sponseller et al ²³ found a significantly higher risk of SSI after scoliosis surgery in patients with cerebral palsy who had undergone instrumentation with unit rods (15%) versus custom bent rods (5%). Furthermore, although stainless steel implants have not been studied in patients with neuromuscular scoliosis, their use in patients with adolescent idiopathic scoliosis has been associated with a higher risk of late deep SSI compared with titanium implants. ^{24 ,​ 25}