General Session: Tumor, Trauma, Infection - Hall F

Presented by: C. Dowe

Author(s):

C. Dowe(1), A. Brecevich(1), T. Callanan(1), D. Lebl(1), F. Cammisa(1), C. Abjornson(1)

(1) Hospital for Special Surgery, Spine Research, New York, NY, United States

Abstract

Introduction: Although pre- and peri-operative antibiotics and skin preparation is performed on all patients undergoing surgery, surgical site infections (SSI) are still considered a significant concern in spinal surgery. One of the most common organisms associated with postoperative infections in orthopedic surgery is Propionibacterium acnes (P. acnes), a constituent of normal, human microbiota that has been identified in 70-95% of healthy human skin. This microorganism is capable of adherence and biofilm formation around instrumentation, leading to risk of infection and failed surgery. The hypothesis of this investigation is that occult bacteria such as P. acnes is still present within the skin and deeper tissues, regardless of pre- and peri-operative prevention, which can lead to poor surgical outcomes for its failure at being detectable during routine pre-operative testing.

Purpose: The objective of this study was to identify the presence of colonized occult bacteria on the skin and in the dermal, subcutaneous fat, ligamentum flavum, and the cancellous bone of the vertebral body utilizing aerobic and anaerobic long cultures in primary posterior lumbar spine surgery procedures.

Methods: This prospective, single-center consecutive series included 54 participants under IRB approval undergoing primary posterior lumbar spine fusions. Prior to surgery, participants underwent standard surgical skin prep and took Ancef antibiotics within an hour of their surgery. Perioperatively, the surgeons took culture swabs of: the skin prior to the incision, the dermal layer of the skin after the incision was made, subcutaneous fat, ligamentum flavum, and cancellous bone after drilling but prior to pedicle screw instrumentation. All culture samples were sent for aerobic and anaerobic long cultures for up to 14 days. Data was analyzed using Binary logistic regression to estimate the incidence of P.acnes in the surgical area. Our primary outcome variable estimated the incidence of positive bacterial organism culture in primary spine fusion procedures, and we hypothesized that preoperative surgical skin prep would be unable to eradicate the occult bacteria, and that the bacteria would still be present within the deeper tissues of the area of procedure.

Results: Occult adherent bacteria were found in 33% of patients undergoing primary spine surgery, with P. acnes being the most prevalent species. Other bacteria, such as Staphylococcus simulans, Staphylococcus epidermidis, and Staphylococcus capitis were also found in the surgical area, with some patients having positive tests for multiple types of bacteria. Although positive cultures were found in the skin after the incision was made, the majority of positive culture samples were found in the samples of subcutaneous fat and bone.

Discussion: The data collected supports our hypothesis that occult bacteria, especially P. acnes, are still present in tissues deep below the skin prior to surgery, regardless of the efforts made by preoperative skin prep and antibiotics. These results show that more studies should be done in order to figure out how occult bacteria can truly be eradicated from the surgical site prior to surgery. The findings of these new studies can change surgical prep methods, as well as intra-operative and post-operative wound management in order to keep the risk of surgical site infection to a minimum.