Surgical site infections (SSIs) are the most frequent adverse event requiring revision after spinal fusion for pediatric scoliosis. The incidence of SSI after adolescent idiopathic scoliosis (AIS) surgery remains highly variable, currently ranging from 0.5% to 7%.1–4 Numerous risk factors have been investigated, but most of them are patient related and therefore nonmodifiable, such as previous surgery or underlying medical status.5–7 Recent literature has focused on deep wound infections management and described prevention strategies to decrease their occurrence, but the influence of the type of instrumentation used for surgical correction remains unknown.3,8–10 All-pedicle screw constructs are currently the most popular, but several limitations have been reported lately, resuscitating interest for posteromedial translation techniques using hybrid instrumentation.11–15 Sublaminar bands in hybrid constructs have therefore proved to provide long-lasting correction forces, but the main concern to date corresponds to the risk of infection, and the ability of the pathogen to colonize the polyester plait, which could make SSI eradication more difficult. In addition, very little literature is available regarding SSI sequelae. As a matter of fact, bone graft is often partially removed during surgical debridement, thus altering the conditions for optimal fusion. In addition, the multiple procedures that can be necessary to eradicate the pathogen and the longer hospitalization stay might lead to poorer satisfaction. The goal of this study was therefore to report the outcomes of SSI in AIS patients operated with hybrid constructs using sublaminar bands.
After institutional review board approval, medical data of all patients operated for AIS in our institution between March 2006 and September 2013 were retrospectively reviewed. Patients with previous spinal surgery or medical conditions increasing the risk for infection were excluded. The cases of infections were first identified, using the recommended criteria, to determine the incidence rate of SSI associated with the sublaminar bands technique.16 Patient-related and procedure-related parameters from the SSI group were then compared with a control group, matched for age, Lenke curve type, and initial Cobb angle.17
On the day of surgery and the day before, all patients took a shower with povidone-iodine scrub. The operative team systematically checked the back skin at the time of admission, and the procedure was postponed in case of significant acne. Skin preparation before incision included 1 surgical site povidone-iodine scrub, followed by two 5% alcoholic povidone-iodine paints performed by a nurse. The surgical field was recovered by an iodine-impregnated adherent plastic drape, and 2 plastic bags were placed laterally to protect the bands from falling down during the procedure.
The same blood-saving strategy was applied during the entire study period. Patients were preoperatively treated by weekly injections of erythropoietin to reach a hemoglobin rate of 15 mg/dL, and antifibrinolytic (tranexamic acid) was systematically used during the procedure.
As recommended, antibiotic prophylaxis relied on cefamandol, with 2 g injected within 1 hour before incision, followed by a second injection of 1 g 4 hours later, and antibiotics were stopped after wound closure.18
All patients underwent posterior segmental spinal correction and fusion using hybrid constructs, performed by one of the 2 senior surgeons of the department, under spinal cord monitoring. Fusion levels were selected following the same criteria during the study period.11 In all cases, pedicle screws were placed at the distal extremity of the curve (from L4 to L1 or T12), whereas thoracic levels were instrumented with sublaminar bands (Universal Clamp; ZimmerSpine, Bordeaux, France or Jazz; Implanet, Bordeaux, France) on the concave side and at the apex on the convex side. The 2 upper thoracic levels, located at the proximal end of the construct, were bilaterally instrumented with autostable hooks (ZimmerSpine), protected by 2 adjacent sublaminar bands (Fig. 1).
Correction was performed using 5.5 mm Ti or CoCr rods, contoured according to the desired sagittal alignment. The lumbar curve was first corrected, and once the last instrumented vertebra was leveled, the rods were connected to the stable proximal anchor with the set screws left loose to allow distraction. The bands were then connected to the rods and multilevel tension was applied on the concave side to obtain a posteromedial translation of the scoliotic curve.12 After tensioning all bands, set screws were revisited and the residual length of the bands were cut and removed. After decortication, autograft was used in combination with bioglass (Novabone; NovaBone Products, Alachua, FL), as previously reported.19 Wound closure was performed over 2 drains after irrigation (1000 mL of sterile saline solution) and muscle debridement.
Postoperative Care and SSI Management
Wound dressings were changed on days 2 and 5 postoperative, with drains being removed on day 2. Patients started to stand on the second postoperative day with the physiotherapist, and worked in erect position twice a day during hospitalization stay. Patients were discharged from the hospital and sent to a rehabilitation center (3 wk period) between 6 and 7 days after surgery. When SSI was diagnosed, patients were treated according to the same standardized protocol, associating serial surgical debridement with irrigation, wound closure without removal or change of the implants, and 15 days of intravenous antibiotherapy administrated through a central catheter placed during the revision procedure, followed by 2.5 months of oral antibiotics adapted to the pathogen. When necessary, serum dosage of antibiotics was given before discharge. In all cases, the antibiotherapy was discussed and decided during a multidisciplinary meeting with the referent surgeon, a pediatrician, and a microbiologist.
Evaluation at Follow-up
Infection eradication was defined as no signs of infection on physical examination, and normal blood parameters, as recommended by Ahmed et al.1 To determine the influence of SSI on fusion and/or instrumentation failure, radiologic analysis was performed preoperatively, postoperatively, and at latest follow-up (minimum 2 y) using low-dose biplanar stereoradiographs (EOS Imaging, Paris, France). In addition, the final functional outcomes were evaluated using SRS 30 and SF 12 questionnaires, and compared with those of a control group, matched for age, sex, body mass index, and number of sublaminar bands.20,21
Demographic data, loss of correction, and functional outcomes were compared between the SSI and the control groups using unpaired t tests (Statview; SAS Institute Inc., Cary, NC). A P<0.05 was considered significant.
Among the 524 patients who underwent AIS correction using sublaminar bands during the study period, 28 (5.3%) were diagnosed with SSI. The average follow-up was 42 months (±16). Early infections (within 45 d postoperative) were reported in 26 of the 28 SSI patients (93%), after a mean free interval of 18 days (±8), whereas 2 late SSI occurred after 84 and 674 days, respectively.
Demographic data of the SSI and control groups are reported in Table 1. No significant difference was found except for the number of levels fused, which was significantly higher in the noninfected group.
Pathogens were identified in all cases, using either direct examination and/or molecular biology. SSI was monomicrobial in 24 cases (86%) and polymicrobial in 4 cases (14%). The most frequent pathogen was methicillin-sensitive Staphylococcus aureus (13 cases, 46%), followed by Propionibacterium acnes (8 cases, 29%), all with community profile. Skin germs (S. epidermidis, S. aureus, and P. acnes) were responsible for the SSI in 86% of cases. No patient presented urinary tract infection postoperatively.
All patients with SSI underwent surgical debridement within 24 hours after diagnosis. More than 1 surgical debridement (2 to 3 total) was necessary in 7 cases (25%) to obtain definitive SSI healing, but no early band removal was performed. The switch to oral antibiotics was possible in all cases after 15 days. Instrumentation removal was decided for the 2 patients with late infections, because the spine was considered fused at the time of SSI. No adverse event occurred when the sublaminar bands were pulled out.
Radiologic and Functional Outcomes After SSI
The radiologic analysis did not find any difference at follow-up between the infected and the control groups. In particular, the SSI did not seem to impact fusion, as no significant difference was found regarding the mean loss of correction in both frontal and sagittal planes at latest examination.
However, one should note that the 2 patients with late infection, in whom implants were removed, respectively, lost 8 and 14 degrees on the main instrumented curve.
Similarly, functional outcomes were not affected by the occurrence of SSI (Table 2). SSI influenced neither postoperative pain, mental health, nor the appearance of the scar, partly traduced by the self-image score. Satisfaction after surgery remained high, despite the infection and revision procedure, with 89% of patients claiming that they would again undergo the same treatment.
SSI Incidence and Management
Results of the current study demonstrate that the use of sublaminar bands in AIS led to a 5.3% incidence rate of SSI. Even though it is in accordance with existing literature, this rate stands in the upper range, and whether or not the bands resulted in an increase in SSI remains uncertain.1–4,22–24 However, results are consistent with a previous study, performed by the same department, in which hooks were used in similar hybrid constructs.13 Sublaminar bands can therefore safely replace pedicle screws or hooks at thoracic levels, to optimize sagittal correction, while reducing operative time, implant density, blood loss, and radiation exposure.25–27 Nevertheless, the use of lateral plastic bags is recommended, as sublaminar bands measure approximately 25 cm long before being tensioned.
Results also show that a concern raised by some surgeons about a higher risk of implant colonization in case of SSI, due to the band structure, was not justified, and that the management of SSI remained unchanged. The fact that 25% of the infected patients underwent multiple debridements (average 1.3/patient) may seem high, but it is comparable to recent published studies, in which the mean number of irrigation and debridement ranged from 1.2 to 2 per patient, in large series of pediatric deformities with multiple etiologies.28–30
As shown in vascular surgery literature about Dacron patches (similar constitution than sublaminar bands), the use of polyester did not increase SSI rate, and the high incidence of late infections reported with Dynesys implants was not observed in the current study.31 In addition, all infections healed after serial debridements and appropriate antibiotherapy, without necessitating band or instrumentation withdrawal, even in cases of early SSI due to P. acnes (7 cases), unlike what had been reported by Collins and colleagues.32–34 In contrast, in cases of late infection in which instrumentation removal was decided to ease pathogen eradication, no adherence with the dura was observed and no intraoperative complication occurred when bands were pulled out, contrary to what was observed with Luque wires.35 After removing the locking screws, rod connectors were opened and unclipped, and then easily taken out from the bands. Both sublaminar extremities of polyester were identified, and after making sure the band was still mobile, it was gently removed from either the cephalic or the caudal part of the lamina.
Deep wound infections can lead to ongoing pain, prolonged hospitalization, osteomyelitis, pseudarthrosis, and even death, depending on patient medical status.30 SSI can therefore be considered as one of the most serious complication that can affect patient outcomes. To date, there is a lack of data regarding the clinical outcomes after AIS SSI to provide accurate information to patients and their families, and balance the mid-term and long-term benefits of deformity correction with the risk of infection.
Results of the current series are consistent with the conclusions of Mok et al36 in adults, and confirm that at the end of SSI treatment, AIS patients can expect medium-term clinical outcomes similar to patients in whom SSI did not occur. Despite a longer hospitalization stay and multiple surgical procedures (1 to 3 irrigation debridements), functional scores remained comparable to those previously published in the literature for noninfected patients.37 In addition, no significant difference was found at follow-up in our series between the SSI and the control group.
The second finding of this study is that no association was reported between early infections and pseudarthrosis, as observed in adults by Katonis et al.38 As a matter of fact, the chosen implant retention strategy led to pathogen eradication in all cases, and no difference was found between groups regarding the average loss of correction at latest radiologic examination. However, the relation between pseudarthrosis and late infections needs to be further assessed, as the 2 patients with late SSI and instrumentation removal, respectively, lost 8 and 14 degrees at 4-year follow-up, which is in accordance with previous reports, ranging from 6 to 10 degrees per year.28,30,39
The first limitation of this study is its retrospective nature, so preoperative functional scores were not assessed and available for comparison. However, all data were prospectively collected over the 7.5-year period, and no case of SSI was lost during follow-up. Second, no real control group of patients instrumented without polyester was included, as posteromedial translation with sublaminar bands has been the unique method used for correction in AIS in our department since 2006. Results were only compared with previous literature with different type of implants, from other institutions, which might include multiple strategy-related and patient-related biases. Still, the incidence rate of SSI remained comparable to a previous published series of consecutive hybrid constructs performed with hooks in the same department, following the same perioperative protocols.13 Finally, the overall incidence of SSI remained high, and large prospective multicenter studies are necessary to further evaluate the influence of different perioperative preventive strategies, and reduce to a minimum the incidence of this serious complication.
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