Abstract
Infection of a total joint replacement (TJR) is considered a devastating complication, necessitating its complete removal and thorough debridement of the site. Usually at least two surgical interventions and antibiotic treatment within a period of several months are estimated being required for a favourable outcome. It is undoubted that one stage exchange, if successful, would provide the best benefit both for the patient and the society. Still the fear of re-infection dominates the surgeons’ decisions and directs them to multiple stage protocols. However, there is no scientifically based argument for that practice. Successful eradication of infection with two stage procedures is reported to average 80% to 98%, whereas there are no significant differences between revisions with or without antibiotic loaded cement, with short or long term antibiotic therapy, with or without the use of spacers and other differences. On the other hand a literature review of Jackson and Schmalzried (CORR 200) summarizing the results of 1,299 infected hip replacements treated with direct exchange (almost exclusively using antibiotic loaded cement), reports of 1,077 (83%) having been successful. For total knee replacement Jaemson et al. (Acta 2009) could show that the overall success rate in eradication of infection was 73–100% after one-stage revisions. It may be calculated, that adding a second one stage procedure for treating the failed cases the overall result with two operations may improve to > 95%, an outcome which is at least as good as the best results after two stage revisions, while requiring only one surgical intervention for the majority of cases.
Spacers have been proven to be useful for improving final functional results compared to temporary resection; however, concerning infection control no benefit could be shown. Dead space management is performed comparably effective by a new prosthesis as with a spacer. In addition a definitive prosthesis is providing increased stability, which a spacer does not. As long as protection against colonization is granted by high local antibiotic concentrations a prostheses is likely to provide better functional results than a spacer.
These results suggest, that the major factor for a successful outcome with traditional approaches may be found in the quality of the surgical debridement and dead space management. Failures in all protocols seem to be caused by small fragments of bacterial colonies remaining after debridement, whereas neither systemic antibiotics nor antibiotic loaded bone cement (PMMA) have been able to improve the situation significantly.
One stage exchange provides marked reduction of patients discomfort and costs but is performed only rarely due to a multitude of risks and disadvantages, related to the mandatory use of antibiotic loaded cement for fixation. Cemented revisions generally show inferior long term results compared to uncemented techniques; the addition of antibiotics to cement reduces its biomechanical properties. The release of antibiotics from cement is too short-lived and concentrations are too low for reliable eradication of eventually remaining pathogens, especially when they are embedded within biofilms. PMMA has been shown to be the ideal substrate for bacterial attachment and replication of sessile bacterial phenotypes. Aging cement releases antibiotics in subinhibitory amounts, leading to antibiotic resistance of adherent bacteria even years after implantation. Whenever a new prosthesis is implanted into a previously infected site the surgeon must be aware of increased risk of failure, both in single or two stage revisions. Eventual removal therefore should be easy with low risk of additional damage to the bony substance in such a case. On the other hand it should also have potential of a good long term result in case of success. Cemented systems seem to be less likely for that purpose since efficient cementing techniques will result in tight bonding with the underlying bone. Eventual removal such will be time consuming and possibly associated with further damage to the osseous structures.
Allograft bone may be impregnated with high loads of antibiotics using special incubation techniques. The storage capacities and pharmacological kinetics of the resulting antibiotic bone compound (ABC) are more advantageous than the ones of antibiotic loaded cement. ABC provides local concentrations exceeding those of cement by more than a 100 fold and efficient release is prolonged for several weeks. The same time they are likely to restore bone stock, which usually is compromised after removal of an infected endoprosthesis. ABC may be combined with uncemented implants which in case of a failure markedly facilitates their removal. There is reduced risk of creating resistances since the stored antibiotics are eluted completely and elution is terminated after several weeks.
Based on this technology new protocols for one stage exchange of infected TJR have been established, both for hips and knees. Bone voids surrounding the implants are filled with antibiotic impregnated bone graft; uncemented implants are fixed in original bone. Recent studies indicate an overall success rate of more than 90% without any adverse side effects. Incorporation of allografts appears as after grafting with unimpregnated bone grafts. The favourable results have initiated extension of the technique to simultaneous reconstruction of large septic defects using impregnated bulk allografts.
Antibiotic loaded bone graft seems to provide sufficient local antibiosis for protection against colonisation of uncemented implants, the eluted amounts of antibiotics are likely to eliminate biofilm remnants, dead space management is more complete and defects may be reconstructed efficiently. One stage revision such should be at least comparably save as multiple stage procedures, taking advantage of the obvious benefits for patients and economy.
Correspondence should be addressed to Vienna Medical Academy, Alser Strasse 4, A-1090 Vienna, Austria. Phone: +43 1 4051383 0, Fax: +43 1 4078274, Email: ebjis2009@medacad.org
