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Local antibiotic carriers are available as resorbable carriers (e.g. gentamicin-loaded collagen) and non resorbable carriers, mostly gentamicin-loaded bone cement in the form of beads or spacers. The release of the antibiotic may differ largely, depending on the properties of the carrier. In the use of spacers the release may remain too low, resulting in subinhibitory gentamicin concentrations. Revision of late deep infection of a knee prosthesis includes extraction, debridement and the use of local and systemic antibiotics. Reimplantation can be performed if healing is appropriate and the bone stock reaches. Otherwise arthrodesis is necessary.

We treated 100 patients having osteomyelitis with debridement and gentamicin-PMMA beads and followed them for 5 (1-12) years. 66 of the infections were chronic, in 18 cases combined with arthritis and in 3 cases with pseudarthrosis. They underwent 117 "treatment periods", consisting of one or more operations (total 152), in most cases with an interval of 2 weeks. No systemic antibiotics were necessary besides the local antibiotic treatment in 52 of the treatment periods. Healing was achieved in 92 patients, in 78 after a single treatment period which included 1-5 operations, in 14 after two or three treatment periods. Healing was more difficult to achieve when the infection was chronic, especially with a duration of more than 6 years or when caused by elective surgery. Local antibiotic treatment with gentamicin PMMA beads has the advantage that the wound can be closed primarily and that a higher local antibiotic concentration in the tissues can be achieved, often making systemic antibiotic treatment unnecessary.

150 gentamicin-PMMA-beads were implanted (+ 160 mg gentamicin i.v. preop.) in a woman aged 73 years and with severely impaired kidney function. Frequent determination of gentamicin plasma concentrations and renal functions were possible. The plasma concentration reached a plateau at approx. 3 micrograms/ml. No accumulation of gentamicin in plasma occurred.

Five patients treated with gentamicin-polymethylmethacrylate (PMMA) beads were monitored during the treatment of nine to 14 days. Kinetic data of the gentamicin delivery were gathered constantly by multiple samples of blood and urine. The treatment with 48-360 beads caused a gentamicin serum concentration of 0.03-0.4 micrograms/ml and a renal excretion rate of 3-40 micrograms/min. The total amount of gentamicin excreted after the whole treatment was 20%-70%, with an in vivo half-life of 5.7-10 days. The gentamicin appeared to be released constantly during the entire treatment (nine to 14 days); the beads are kinetically slow release carriers. Despite precise measurement of tubular and glomerular renal function, no nephrotoxicity could be demonstrated. This local antibiotic gentamicin therapy may use the blood bone barrier effectively as a protection of the body against a very high local gentamicin concentration.