Infection can occur after any spinal procedure that violates the disc and although it is not common, the potential consequences are serious. Treatment of
discitis is not always successful and the key to management is prevention. Intradiscal prophylaxis with
antibiotic is routinely used in spinal surgery, but there is a limited understanding of how well
antibiotics can enter the avascular disc after
intravenous injection. An in vivo ovine study to optimise prophylactic and parenteral treatment of
discitis is described to assess the effectiveness of
cephazolin in preventing and treating
infection. The concentration of
cephazolin was measured in disc tissue from normal and degenerate sheep discs to determine if
cephazolin can enter the disc and if
disc degeneration affects
antibiotic uptake. Fourteen sheep were deliberately inoculated with bacteria to induce
discitis. Eight sheep ("prophylaxis" group) were given either a 0, 1, 2 or 3 g dose of prophylactic
cephazolin before inoculation while the remaining sheep ("treatment" group) were treated with
cephazolin commencing 7 days after inoculation for 21 days at a dose of 50 mg/kg/day. Histopathology and radiography were used to assess the effect of the different treatments.
Cephazolin was given 30 min prior to sacrifice and the intradiscal concentration was measured by biochemistry. In the "prophylaxis" group all doses of
antibiotic provided some protection against
infection, although it was not dose dependent. In the "treatment" group
discitis was confirmed radiologically and histologically in all animals from 2 weeks onwards. Biochemical assay confirmed that
antibiotic is distributed throughout the disc but was present in higher concentration in the anulus fibrosus than the nucleus pulposus. This study demonstrated that whilst the incidence of iatrogenic
discitis can be reduced by
antibiotic prophylaxis, it could not be abolished in all incidences with a broad-spectrum
antibiotic such as
cephazolin. Furthermore,
antibiotics were ineffective at preventing endplate destruction once an intradiscal inoculum was established.