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Updated: Dec 20, 2025
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Published on: June 23, 2020
Prevalence of Occult Infections in Posterior Instrumented Spinal Fusion
Tucker C Callanan1, Celeste Abjornson2, Edward DiCarlo2
1New York Medical College, Valhalla.
Study Design:
This is a prospective observational study.
Objective:
The aim of this study is to determine the rate of occult infection after instrumented spine surgery in presumed aseptic patients.
Summary Of Background Data:
The reported incidence rate of delayed/occult infection determined by positive culture swabs after instrumented spine surgery in prospective studies is 0.2%-6.9%. However, this rate may be higher as delayed infections are challenging to diagnose. Fever can be absent and inflammatory markers are often normal. If indolent organisms exist in low concentrations surrounding the instrumentation, these organisms can possibly avoid detection and disrupt bone formation leading to instrumentation loosening, pain generation, and/or failure of a solid fusion.
Materials And Methods:
This study included 50 consecutive presumed aseptic patients undergoing a posterior revision requiring removal of instrumentation at least 6 months following their index procedure. Common markers of infection were examined preoperatively. Multiple culture swabs were taken directly from the removed instrumentation and cultured for 14 days.
Results:
Of the 50 patients, 19 (38%) were culture-positive (CP) for bacteria upon removal of their instrumentation, with 14 patients (28%) having ≥2 positive specimens of the same organism. The average length of time between the index procedure and the revision surgery was 4.55 years (range: 0.53-21 y). Polymicrobial infections were found in 26% (5/19) of CP patients. The most prevalent microorganism found was Propionibacterium acnes, in 63% (12/19) of CP patients. There was no significant difference between CP and culture-negative patients regarding preoperative markers for infection, age, or length between index and revision procedures.
Conclusions:
The results of this study indicate a positive culture rate of 38% in presumed aseptic patients who had previously undergone instrumented spine surgery. These results are consistent with other retrospective studies and are >6 times greater than any previous prospective study utilizing culture swabs.
Level Of Evidence:
Level-III.
Insights
A significant 38% of patients undergoing instrumented spine surgery revision showed positive cultures, indicating a high rate of occult infection. This challenges previous prospective findings and highlights the need for better diagnostic methods for post-surgical spinal infections.
Area of Science:
- Spine Surgery
- Infectious Diseases
- Microbiology
Background:
- Delayed or occult infections after instrumented spine surgery are difficult to diagnose, with reported prospective incidence rates of 0.2%-6.9%.
- Low-concentration, indolent organisms can evade detection, leading to complications like instrumentation loosening and failed fusion.
- Traditional infection markers (fever, inflammatory markers) are often normal in these cases.
Purpose of the Study:
- To determine the incidence rate of occult infection in patients with presumed aseptic conditions following instrumented spine surgery.
- To investigate the presence of bacterial contamination on removed instrumentation in revision surgeries.
Main Methods:
- Prospective observational study involving 50 patients undergoing posterior revision surgery with instrumentation removal at least 6 months post-index procedure.
- Preoperative assessment of common infection markers.
- Collection of multiple culture swabs directly from removed instrumentation, with 14-day incubation.
Main Results:
- A 38% (19/50) culture-positive rate was observed upon instrumentation removal.
- 14 patients (28%) had ≥2 positive specimens for the same organism; 26% of positive cases were polymicrobial.
- Propionibacterium acnes was the most prevalent organism (63% of positive cultures). No significant differences in preoperative markers, age, or time to revision were found between culture-positive and culture-negative groups.
Conclusions:
- The study reveals a 38% positive culture rate in presumed aseptic patients after instrumented spine surgery, significantly higher than previously reported in prospective studies.
- These findings suggest a higher prevalence of occult spinal infections than previously estimated.
- The results underscore the limitations of current diagnostic methods and the potential for undetected infections to impact surgical outcomes.
