General Session: Tumor, Trauma, Infection, Image

Presented by: T. Callanan - View Audio/Video Presentation (Members Only)

Author(s):

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

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

Abstract

Introduction: Often in revision spinal surgery, chronic pain and/or pseudoarthrosis are the main indications, and normal screening rules out the presence of infection. If insidious organisms exist in low concentrations in a biofilm that surrounds the majority of implant surfaces and may be identifiable only after non-routine longer culture times, these organisms can disrupt bone formation leading to micro-motion (pain generation) around the implants or failure of a solid fusion. Occult spinal infections provide a differential diagnoses to be considered in patients experiencing chronic pain when surgical parameters such as fusion status and hardware placement are normal. The purpose of this investigation was to ascertain the incidence of occult pathogens in revision spinal surgery, as well as identify properties in the spinal implants that may have predisposed them to infections.

Materials/Methods: Under IRB approval, implant retrievals of a prospective, consecutive series of thirty-eight adult patients undergoing a posterior revision in either the cervical (2), thoracic (1), or lumbar (35) spine requiring hardware removal were studied. Patients who had experienced a traumatic event since the primary surgery, were affected by an autoimmune disease, or were known to have infected hardware based on preoperative serological testing were excluded from the study. Perioperative antibiotics were held until hardware removal and swabs had been taken. Swabs were taken in each screw hole and around each screw head for long cultures (14 days). The hardware was catalogued and analyzed for wear by light microscopy and scanning electron microscopy. Cultured samples were embedded for histological examination to quantify the existence of colonies of bacteria in proximity to the implant. A regression analysis was performed to find the relationship of variables collected to determine predictive indicators of occult pathogens.

Results: Occult adherent bacteria were found in 39% (15/38) of the tissue surrounding the implants of patients undergoing spine revision surgery. The most prevalent bacteria found were P. acnes, in 47% (7/15) of the infected patients. Other cultures grew Klebsiela pneumoniae, Coccobacilli, Trueperella bernardia, Staphylococcus simulans, Staphylococcus saccharolyticus, Staphylococcus warneri, Staphylococcus epidermidis, as well as Staphylococcus capitis. Bacteria took on average five days to grow out on culture plates. Etching and pitting consistent with normal wear and removal was visible on each implant analyzed via SEM, but not abnormal to revision surgeries collected for known pathologies. There was no direct correlation between implant parameters, length between index and revision procedures or surgical location. There were nearly equal numbers of females (18) and males (20) included in the study, however males showed a significantly higher incidence of positive culture results (11/20) then females (4/18).

Conclusion: The findings of this study suggest that occult infections are far more prevalent in patients requiring revision surgery than previously identified. The study also suggests that long term cultures are vital to identifying these pathogens as bacteria took on average five days to grow out on culture plates. Finally, the findings suggest that males were more susceptible to occult infections then women. Identifying the factors that contribute to failed surgery and/or chronic pain are critical. The results of this study demonstrate that occult infections could be a contributing factor to this issue.