Vancomycin powder mixed with autogenous bone graft and bone substitute may decrease the deep surgical site infections in elective lumbar instrumented fusion surgery for degenerative disorders: a prospective randomized study.

Background context: Deep surgical site infections (DSSI) following lumbar instrumented fusion surgery are associated with considerable morbidity. Intraoperative application of vancomycin powder (VP) has been widely used to prevent DSSI; however, the effects of VP mixed with local autogenous bone graft (ABG) and bone substitute on DSSI prevention and bone fusion remains unclear.

Purpose: To examine the effects of VP mixed with ABG and bone substitute on DSSI and fusion rate.

Study design/setting: A prospective randomized case-controlled study at a single medical center. (ClinicalTrials.gov Identifier: NCT03883022) PATIENTS' SAMPLE: Adult patients who underwent decompression along with instrumented fusion surgery for a degenerative lumbar condition were recruited from October 2017 to May 2023. Patients were randomly allocated to vancomycin (n=357) or control (without vancomycin) (n=348) groups. In the vancomycin group, 1 g of antibiotic powder was used for 2- and 3-level fusions (no 1 level fusions?) while 2 g was used for >3-level.

Outcomes measures: The primary outcome was DSSI within 90 days after index surgery. Secondary outcomes included surgical and vancomycin-related complications, functional outcomes and bone fusion.

Methods: All patients were followed up with plain spine radiographs at 1, 2, 3, 6, and 12 months after surgery. The definition of DSSI was based on the Centers for Disease Control and Prevention criteria for SSI. Posterolateral fusion was assessed using the Lenke criteria and interbody fusion was assessed using the Brantigan-Steffee-Fraser (BSF) definition. Solid fusion was defined as an angular change of <5° of the fused segments in supine dynamic flexion and extension lateral radiographs, Lenke grade A and B or BSF-3 definition. Antibiotic concentrations in the vancomycin group were measured in the serum and at the surgical site in the drain on days 1 and 3 after the index surgery. Functional outcomes were evaluated by Oswestry Disability Index (ODI) and visual analog scale (VAS) for leg pain.

Results: In total, 357 and 348 patients were enrolled in the vancomycin and control groups, respectively. Mean patient age was 67.7±11.0 years and 63.0% were female. There were no DSSIs in the vancomycin group and five in the control group (0 vs. 1.4%, p=.029). All five patients with DSSI had diabetes (100%). None of the patients with diabetes in the vancomycin group developed DSSI (0/119 vs. 5/105 in control group, p=.021). Postoperative serum vancomycin levels were undetectable and no vancomycin-related complications were observed. The mean vancomycin concentrations at surgical site in the drain were 524.5±209.9 μg/mL and 217.4±97.2 μg/mL on postoperative days 1 and 3, respectively (measured in a drain?). At the final follow-up, functional outcomes and bone fusion rates were similar between the two groups. Solid posterolateral fusion (Lenke grade A or B) was observed in 79.3% (257/324) of the vancomycin group and 73.5% (233/317) of the control group (p=0.348). Interbody fusion, based on the BSF-3 definition, was observed in 99.4% (326/328) of cages in the vancomycin group and 99.6% (258/259) in the control group (p=1.000). Based on the criteria of angular change of < 5° on dynamic lateral radiographs, the solid fusion rate was 100% in both groups.

Conclusions: Vancomycin mixed with local ABG and bone substitute maintains high vancomycin level at surgical site and appears safe and effective for preventing DSSI in lumbar degenerative instrumented fusion surgery without affecting bony fusion, especially in diabetic patients.

Trial registration: ClinicalTrials.gov Identifier: NCT03883022.