Benefits of Articulated PMMA Spacers in Total Knee ReplacementsPatients with an infected joint after total knee replacement (TKR) need treatment as quickly and as effectively as possible. The consequences of implant and/or joint infection can be very serious. The surgeon does everything possible to save the implant, the knee, and the patient.
In this report, surgeons from the University of Queensland in Australia discuss the use of using polymethyl methacrylate (PMMA) spacers in such patients.
Once an infection is discovered, the implant is removed. The joint is cleaned and rinsed thoroughly of all bacteria. This step is called debridement. Then the joint is treated directly with antibiotics. A special device called a spacer coated with antibiotics is put in the space left by the removed implant.
Using a spacer has several advantages. It holds the soft tissues at just the right tension until the implant can be put back in the joint. Static spacers do not move or allow joint motion. The patient can't put weight on this type of spacer. It's possible the spacer can crush some of the bone.
But a static spacer is better than no spacer at all. It keeps the space from filling in with dense scar tissue. The next step up is an articulating PMMA spacer. This type allows for controlled motion of the knee. It holds the space open, keeping a normal amount of tension and balance between the bones, muscles, and ligaments.
There are different methods used for implant removal, debridement, and reimplantation. The surgeon may sterilize the original implant, coat it with antibiotics, and put it back into the joint.
Or a custom-made PMMA spacer is constructed right in the operating room. The surgeon can use the most effective antibiotic for the type of bacteria present. A polyethylene (plastic) liner between the bone and implant is another option. It can be cemented in place with PMMA filled with antibiotics.
Using these techniques, the infection can be controlled. It is also possible to keep the infection from coming back using the PMMA spacers. Using a spacer is a two-stage method of treatment. When the infection is cleared up, then the spacer can be removed and replaced with another implant. This final step is called exchange arthroplasty.
Kevin Tetsworth, and Jodi Dennis. Contemporary Management of Infected Total Knee Replacement. In Current Opinion in Orthopaedics. Vol. 19. No. 1. Pp. 75-79.
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