Factor	Conclusion
Patient-associated factors
Age	In general, the literature suggests a mixed finding of association between age and SSI.
Diabetes mellitus (DM)	In general, the literature suggests a strong association between DM/A1c and SSI.
General comorbidities	In general, the literature has mixed finding of specific comorbid conditions in association of SSI. There is evidence to suggest higher number of comorbidities is associated with SSI.
Nutrition	In general, the literature suggests malnutrition is associated with SSI.
Smoking	In general, the literature has mixed results of association between smoking and SSI. More recent evidence would suggest there is correlation between the two.
Obesity/Body mass index	In general, the literature suggests a strong association between obesity and SSI.
Surgery-associated factors
Time and duration of surgery	In general, the literature is mixed, with conflicting results, making it difficult to firmly establish an association.
Surgical approach/Invasiveness	In general, the literature is mixed with general trend indicating combined approach have highest incidence of SSI, followed by posterior approach. There is strong evidence increased invasiveness is associated with SSI.
Perioperative interventions	Preoperative radiation and postoperative blood transfusion have strong association with SSI. There is mixed evidence of UTI/urinary catheter in association of SSI.
Surgical team	In general, there is mixed evidence of resident/fellow involvement, number of surgeons and SSI, unable to establish an association.
Intraoperative concerns and complications	There is mixed evidence of intraoperative blood loss, dural tear, hypothermia and SSI, no established association can be made.