What’s the Claim?
Using intrawound vancomycin powder suspended in fibrin glue plus routine intravenous antibiotics was associated with a lower risk of surgical site infection (SSI) in patients undergoing posterior spinal instrumentation surgery for a variety of diagnoses when compared with IV antibiotics alone. The unadjusted risks of infection were 2.2% versus 8.5%, respectively, and even after adjusting for confounders, the risk reduction with vancomycin in fibrin glue persisted (the odds ratio of 0.25 after adjustment reflects an approximate fourfold odds difference, not very different from the unadjusted finding).
How’s It Stack Up?
Any nonrandomized study on this topic must contend with the fact that a large randomized trial found intrawound vancomycin powder did not reduce the risk of bacterial infection. However, despite randomizing over 900 patients, that study likely was underpowered, given that fewer than 2% of patients in both the treatment and control groups developed infections — a small meta-analysis of three randomized controlled trials (RCTs) had both the same main finding and the same problem. The advanced statistical model used in the study here was well done and is the next best thing to an RCT. The fact that this study had a higher baseline risk of infection was advantageous in that the high event rate made it easier for the authors to discern a benefit from the treatment. Of course, it causes one to wonder why over 8% of patients who did not get intrawound antibiotics got SSIs, and why intrawound antibiotics only reduced that percentage down to about what most of us think it ought to be without intrawound antibiotics.
What’s Our Take?
Spinal infections are devastating, so we’re all interested in finding ways to decrease their frequency. Fibrin glue is an appealing way to deliver vancomycin powder — it’s absorbed within the wound, it doesn’t need to be removed (like polymethyl methacrylate cement), it can be sprayed over spinal instrumentation, and it’s soft, meaning spine surgeons are comfortable using it when the dura and nerves are exposed. As for the high overall infection risk in this series, we suspect the authors used vancomycin powder suspended in fibrin glue on the tougher procedures; this series included patients with tumors among other large interventions. The bottom line is this: Another RCT on the topic of intrawound antibiotics isn’t likely to be forthcoming, and we all have some patients whom we feel are at real risk for a bad complication. Here, if there was a selection bias, it likely was to use vancomycin in fibrin glue in patients deemed to be at higher risk for infection, and despite that, those patients still did better. This is something worth thinking about if you’ve got a tough one coming up. Finally, we believe this is an off-label use, and so if you’re going to employ it, you should disclose the risks and benefits of this specific intervention to patients before surgery and document that you did so in the patient's medical record.
Higashi T, Kobayashi N, Ide M, Uchino Y, Inoue T, Inaba Y. The Effect of Local Administration of Vancomycin Suspended in Fibrin Glue for Prevention of Surgical Site Infection After Spinal Instrumentation: Comparison by Probability of Treatment Weighting Model. Spine (Phila Pa 1976). 2023;48:384-390.