Impact of Intervertebral Disc Degeneration and Endplate Changes on Cefazolin Penetration into the Intervertebral Disc.

Background and Objectives: Preoperative cefazolin is the standard of care for intervertebral disc surgery as it reduces the incidence of iatrogenic spondylodiscitis. The aim of this study was to determine the impact of intervertebral disc degeneration and endplate changes on the penetration of prophylactic cefazolin into the intervertebral disc during spinal surgery. Materials and Methods: Adult patients undergoing single-level microdiscectomy for lumbar disc herniation received prophylaxis with 2 g of cefazolin. Venous blood and intervertebral disc samples were collected and analyzed using high-performance liquid chromatography to determine cefazolin concentrations. The severity of intervertebral disc and endplate changes was assessed on magnetic resonance images using the Pfirrmann and Modic grading systems. Results: Cefazolin concentrations were significantly higher in cases with Modic type II changes compared to type 0/I (14.6 ± 9.2 µg g-1 vs. 10.2 ± 4.5 µg g-1 and 9.2 ± 4.1 µg g-1; p = 0.01). 35.4% of patients with Modic type II changes had concentrations > 16 µg g-1, compared to 10% and 25% for patients with Modic type 0/I (p = 0.008). For Pfirrmann grading, 34.6% of grade V discs reached >16 µg g-1 versus 16.7% and 20.3% for grades III and IV (p = 0.26). Patient age, weight, and timing showed no significant correlations with intradisc concentrations. Conclusions: Ninety-four percent of disc samples exceeded the minimum inhibitory concentration for Staphylococcus aureus (>4 µg/g), but considerable variability in cefazolin levels was observed, with higher concentrations in discs showing Modic type II changes.