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Identifying, treating infected TKAs a challenge
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When it comes to swelling, pain and redness in knees pre- and postoperatively, the line between recovery and infection can get blurry.
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�One of the problems with being a knee surgeon is that the four cardinal signs of infection: warmth, redness, swelling and pain, are all part and parcel of a normal and successful knee replacement � and it robs us sometimes of the ability to identify infections,� said Robert E. Booth, Jr., MD. He, along with Arlen D. Hanssen, MD, gave guidance for navigating the murky waters of knee infection, prostheses, and treatment at the 21st Annual Current Concepts in Joint Replacement Winter 2004.
The problem of identifying and treating infections is further compounded by technology that has not advanced as quickly as pathogens. �If you look at our current techniques for diagnosing infections neurological and biologic tests even lumping them all together with scans, our diagnostic accuracy is probably around 80% to 85%,� Booth said. �So we�re missing one infection in five when we look at a painful knee.�
How should physicians handle this issue? Rely on experience and observation, advised Booth, an orthopedic surgeon with the Hospital at the University of Pennsylvania in Philadelphia. �The clinical impression of the knee trumps all the other tests,� Booth said. �If you see a knee that looks infected, it is infected, whether the tests say so or not because of our inability to have a precise diagnosis.�
At the same time the initial inclination after surgery is to give inflamed patients antibiotics but physicians should instead simply aspirate the knee.
Preop, diabetic and elderly patients present specific concerns regarding infection. According to Booth, the molted skin of clients with diabetes may camouflage subcutaneous fat necrosis. Because the skin is unhealthy, he suggests abandoning the site.
As people age the inflammation is not readily apparent through laboratory testing. Therefore, Booth said, a �healthy� knee may be exposed as an afflicted knee during surgery. In some cases, the preoperative erythema doesn�t require surgical procedure, but patience. One common condition for older patients is cellulitis. Instead of operating on patients immediately, Booth suggests waiting one to two days for the condition to clear. Similarly, he advises patients with psoriasis to manage their aliments prior to surgery to decrease the chances of infection.
When aspirating cellulitic cases postoperatively, Booth cautioned that surgeons should avoid access through the skin. Otherwise, joint mobility could be jeopardized. He further cautioned that watching and waiting for the irritation to go away for too long can lead to a serious abscess. When hematomas begin to seep, he advised suction and returning patients to the operating room if necessary.
Redness is often the hallmark of re-cooperation, but sometimes postoperative care can be the culprit. Booth also noted that continuous passive motion machines can lead to bruises and ulcers that require surgery, and sterile solutions containing iodine and ice packs can cause erythema.
Erythema, though common, should always be taken seriously, Booth said. �Remember, not all these red spots are benign,� Booth said. �It has been said that the official color of orthopedics should not be red, but pink, a combination of blood, puss and tears.�
When prostheses are involved, successful diagnosis and time are crucial to a successful recovery said Hanssen, an orthopedist with the Mayo Clinic in Rochester, MN. Hanssen said that the key decision is whether the implant can be saved or other methods should be explored. He recommended antibiotics for weak viruses and patients with stable implants. This treatment works for one-third of patients.
He prescribed debridement to retain prostheses in cases with early (first month) postoperative and acute infections, and cited a 50% to 75% treatment success rate. Afflictions involving functioning prostheses with late infections � acute hematogenous infections � carried a 50% success rate. Hanssen said using an arthroscope during this operation has about a 30% success rate and can lead to long-term infection if not adequately done, he noted. Therefore he suggested incision exposure.
Joint fusion, though used frequently in the past, should only be considered in cases with disruption of the extensor mechanism, Hanssen said. Similarly, he advocated against single-stage reimplantation. �And I think that it�s quite clear in the current era with increasingly worse organisms, and the experience with the bone loss in these organisms, that nobody really advocates this in the knee anymore,� Hanssen said. �I�m sure you can find somebody somewhere [to do it], but I strongly believe that the two-stage reimplantation is the gold standard and we should expect approximately a 90% success rate using this with all comers.�
For late chronic infection, physicians must remove the implant, Hanssen said. With the advance of multiple-treatment resistant viruses, Hanssen uses high- dose antibiotic cement when re-inserting implants. He advises against using beads in hip and knee surgery. �These get stuck in scar and are very difficult to get out,� Hanssen said. �And there�s really no reason to use beads in the hip or knee in contrast to long bone osteomitolitious.�
To combat infection in bone canals, 40% of which contain pathogens, Hanssen injects a dowel of half portion cement with two parts each of vancomycin and gentamicin.
For more information:
- Booth R, Jr. The red knee: a martian nightmare! #90. Hanssen A. The infected knee: all my troubles now. #91. Both presented at 21st Annual Current Concepts in Joint Replacement Winter 2004. Dec. 8-11, 2004. Orlando, Fla.