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Updated: Jan 6, 2026
In Vivo Mouse Model of Spinal Implant Infection
Published on: June 23, 2020
Effects of Intraoperative Intrawound Antibiotic Administration on Spinal Fusion: A Comparison of Vancomycin and
Wataru Ishida1, Alexander Perdomo-Pantoja1, Benjamin D Elder2
1Department of Neurosurgery, Johns Hopkins University School of Medicine, Baltimore, Maryland.
Background:
Local, intrawound use of antibiotic powder, such as vancomycin and tobramycin, in spinal fusion surgery has become an increasingly common prophylactic measure in an attempt to reduce rates of postsurgical infection. However, the effects of localized antibiotic delivery on fusion remain unclear. The objective of this study was to examine the in vivo effects of intraoperative local delivery of 2 antibiotics commonly used in bone-grafting surgery on spinal fusion outcomes in a rat model.
Methods:
Single-level (L4-L5), bilateral posterolateral intertransverse process lumbar fusion surgery was performed on 60 female Lewis rats (6 to 8 weeks of age) using syngeneic iliac crest allograft mixed with clinical bone-graft substitute and varying concentrations of antibiotics (n = 12 each): (1) control without any antibiotics, (2) low-dose vancomycin (14.3 mg/kg), (3) high-dose vancomycin (71.5 mg/kg), (4) low-dose tobramycin (28.6 mg/kg), and (5) high-dose tobramycin (143 mg/kg). Eight weeks postoperatively, fusion was evaluated via micro-computed tomography (µCT), manual palpation, and histological analysis, with blinding to treatment group. In the µCT analysis, fusion-mass volumes were measured for each rat. Each spine specimen (L4-L5) was rated (manual palpation score) on a scale of 2 to 0 (2 = fused, 1 = partially fused, and 0 = non-fused).
Results:
The mean fusion-mass volume on µCT (mm) was as follows: control, 29.3 ± 6.2; low-dose vancomycin, 26.3 ± 8.9; high-dose vancomycin, 18.8 ± 7.9; low-dose tobramycin, 32.7 ± 9.0; and high-dose tobramycin, 43.8 ± 11.9 (control versus high-dose vancomycin, p < 0.05; and control versus high-dose tobramycin, p < 0.05). The mean manual palpation score for each group was as follows: control, 1.46 ± 0.58; low-dose vancomycin, 0.86 ± 0.87; high-dose vancomycin, 0.68 ± 0.62; low-dose tobramycin, 1.25 ± 0.71; and high-dose tobramycin, 1.32 ± 0.72 (control versus high-dose vancomycin, p < 0.05). The histological analyses demonstrated a similar trend with regard to spinal fusion volume.
Conclusions:
Intraoperative local application of vancomycin, particularly at a supraphysiological dosage, may have detrimental effects on fusion-mass formation. No inhibitory effect of tobramycin on fusion-mass formation was observed.
Clinical Relevance:
When spine surgeons decide to use intraoperative intrawound antibiotics in spinal fusion surgery, they should weigh the reduction in surgical site infection against a possible inhibitory effect on fusion.
Insights
High-dose vancomycin impaired spinal fusion in rats, while tobramycin showed no negative effects. Surgeons should balance infection prevention with potential fusion inhibition when using intrawound antibiotics.
Area of Science:
- Orthopedic Surgery
- Infectious Disease
- Biomaterials Science
Background:
- Local antibiotic powder use in spinal fusion aims to prevent infection.
- The impact of these antibiotics on spinal fusion outcomes is not well understood.
Purpose of the Study:
- To investigate the in vivo effects of vancomycin and tobramycin on spinal fusion in a rat model.
- To assess the impact of varying antibiotic concentrations on fusion mass formation.
Main Methods:
- Lumbar spinal fusion surgery was performed on 60 rats.
- Rats received varying doses of vancomycin or tobramycin mixed with bone graft substitute.
- Fusion was evaluated using micro-computed tomography (µCT), manual palpation, and histology.
Main Results:
- High-dose vancomycin significantly reduced fusion mass volume compared to controls (p < 0.05).
- Tobramycin did not show an inhibitory effect on fusion mass.
- Manual palpation scores also indicated reduced fusion with high-dose vancomycin (p < 0.05).
Conclusions:
- Intraoperative vancomycin, especially at high doses, may negatively impact spinal fusion.
- Tobramycin did not demonstrate inhibitory effects on fusion.
- Surgeons must consider the potential trade-off between infection reduction and fusion efficacy when using intrawound antibiotics.
