Surgical site infections in spinal surgery: from risk factors to surgical outcomes

Student thesis: Doctoral thesis


Over the last decade there has been a significant increase in volume of spinal surgeries performed as well as in medical and surgical complexity of patients. This was accompanied by an increased overall morbidity and volume of complications. At the same time, health care professionals have become more aware of the impact of specific preventable complications such as surgical site infections (SSI) and huge efforts have been directed to reduce SSI incidence. Although the general risk factors for SSI have been discussed, the relationship of neurologic status and trauma to SSI has not been explicitly explored. In addition, the direct and indirect impact of deep SSI on surgical outcomes especially after adult spinal deformity (ASD) surgery is still unclear. The aim of this doctoral thesis is to review the risk factors for developing a SSI after spine surgery, as well as how SSI affects clinical outcome. It mainly focuses on diagnosis (Traumatic vs. Degenerative) and neurological status (Spinal Cord Injury SCI or Myelopathy MP) as predictors for SSI. It also reports the associated morbidities and costs of SSI and evaluates the surgical outcomes after SSI. The National Inpatient Survey (NIS) and the Thomas Jefferson University Hospital (TJUH) databases were probed to analyse infection in patients with primary cervical surgery. Using a multivariate analysis, all interplaying comorbidities and risk factors have been. A subsequent resource utilization analysis has been done. The European Spine Study Group (ESSG) prospective database was used to study the functional and clinical outcomes of SSI in patients with posterior fusion for Adult Spinal Deformity (ASD) through the comparison of matched cohorts. Readmissions, reoperations, deformity correction and fusion rates were also studied. A total of 1,247,281 and 5,540 patients met inclusion criteria in the NIS and TJUH databases respectively. SSI incidence was 0.73% (NIS) versus 1.75% (TJUH). It increased steadily from 0.52% in patients without MP to 1.97% in the traumatic SCI group in the NIS data and from 0.88% to 5.54% in the TJUH. Differences between diagnostic groups and cohorts reached statistical significance. SSI was predicted significantly by neurological status (odds ratio [OR] 1.69, p<.0001) and trauma (OR 1.30, p=.0003) in the NIS data. Other significant predictors included: approach, number of levels fused, female gender, black race, medium size hospital, rural hospital, large hospital, western US hospital and Medicare coverage. In TJUH, only trauma (OR 2.11, p=.03) reached significance when accounting for comorbidities. Costs of infection varied among diagnostic groups and summed $184060 in the SCI group. Patients with SSI were also more likely to be discharged to specialized institutions. 444 surgical ASD patients with more than 2 years of follow-up were identified. 20 sustained an acute SSI and 60 controls were accordingly matched. No differences were observed between groups in preoperative radiological and HRQoL variables confirming comparable groups. SSI patients had longer hospital stay and more mechanical complications including proximal junctional kyphosis. Infection was associated with more unrelated complications and revisions. Deformity correction was maintained equally at the different time intervals. One death was related to SSI. SSI patients had worse overall HRQoL status at 1 year and were less likely to experience improvement. However, no significant differences were recorded thereafter. As a conclusion, both primary diagnosis (trauma vs. degenerative) and neurologic status (MP or SCI) were found to be strong and independent predictors of SSI in cervical spine surgery. Also, SSI significantly affects the first postoperative year after posterior ASD surgery. It is associated with more complications, unrelated revisions, and worst quality of life. However it's negative impact seems to be diluted by the second postoperative year.
Date of Award12 Nov 2018
Original languageEnglish
SupervisorFerran Pellise Urquiza (Director), Rodriguez Pardo Maria Dolores (Director) & Carlos Pigrau Serrallach (Director)


  • Infection
  • Surgery
  • Spine

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