• Søren Ohrt-Nissen, Blaine Fritz, Lars Valentin, Kasper Nørskov Kragh, Claus Manniche, Benny Dahl, and Thomas Bjarnsholt.
• Spine Unit, Department of Orthopaedic Surgery, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100, Copenhagen, Denmark. ohrtnissen@gmail.com.
• Eur Spine J. 2019 Dec 1; 28 (12): 2996-3002.

HypothesisTo assess whether a chronic bacterial infection is present in a subset of patients with pseudarthrosis after instrumented spinal fusion.MethodsThis was a prospective diagnostic study including adult patients with previous instrumented spinal fusion. Patients underwent revision surgery for either pseudarthrosis or other causes (e.g. implant removal, curve progression or junctional kyphosis) (control group). Five separate biopsies were randomly collected, intraoperatively, from the pseudarthrosis site and cultivated under both aerobic (5 days) and anaerobic (14 days) conditions. If cultivation was positive in at least 2/5 tissue samples, the biopsy was sectioned and stained using peptide nucleic acid fluorescence in situ hybridization (PNA-FISH). Confocal laser scanning microscopy was used to examine the sections and visualize bacterial aggregates.ResultsThe study included 32 pseudarthrosis and 32 control patients. Cultivation yielded bacteria in at least 1/5 biopsies in 52% of patients with no difference between the groups (p = 1.0). Bacteria of the same species was found in at least 2/5 samples in seven pseudarthrosis patients and four controls (p = 0.509). Propionibacterium acnes was found in 8 of these 11 samples. Microscopy demonstrated tissue-embedded bacterial aggregates in two of these patients but with no inflammatory cells indicating an active infection. The presence of bacteria was not associated with the number of previous spinal procedures or the pre-revision fusion length (p ≥ 0.503).ConclusionsPseudarthrosis after instrumented spinal surgery was not significantly associated with the presence of bacteria at the pseudarthrosis site. Positive cultivation results are common after spinal instrumentation, but our results indicate that they rarely represent an organized infection. These slides can be retrieved under Electronic Supplementary Material.

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