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Early implant loosening, dislocation may signal infection
Multiple culturing and histology can quickly identify methicillin-resistant bacteria.
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BIRMINGHAM, England — Orthopedic surgeons play a major role in diagnosing and managing infections in total joint replacement. They can help their patients achieve optimal outcomes from needed revision surgeries and greatly reduced reinfection rates.
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But to do that clinicians need to familiarize themselves with the classical signs that a joint is infected, assess the infection risk preoperatively, and employ sampling techniques that are effective for identifying the organisms, according to Anthony Berendt, BM, BCh, FRCP.
He emphasized the need for early diagnosis of methicillin-resistant Staphylococcus aureus (MRSA) and other infections. “A lot of harm that these things cause comes from ineffective actions early on.�
Berendt presented current methods for detecting and diagnosing joint infections at the British Orthopaedic Association Annual Congress. He works in the U.K. National Health System’s Bone Infection Unit and is medical director of Nuffield Orthopaedic Centre, Oxford. Last year his institution reported only a single case of MRSA bacteremia (bloodstream infection).
Acute or chronic infection?
What total joint replacement surgeons do in these cases depends greatly on whether the infection is acute or chronic, Berendt told Orthopedics Today. Acute infections “usually arise early … before the wound’s even healed. With an organism like MRSA, there is usually clinical evidence of infection in the wound itself. So in a sense, diagnosing that presentation is not especially difficult. It’s much more difficult when you have chronic infection that may not always be accompanied by a wound infection,� he said.
A major sign of acute infection in a replaced knee or hip joint is prolonged wound drainage beyond five days postop, which might indicate a hematoma. A large wound surveillance study conducted in Minneapolis identified hematoma as a major risk factor for superficial infection.
Pain and joint dislocations signal more chronic infection, as does a loosened prosthesis that needs revising. “Certainly unexplained early failures should ring lots of alarm bells,� he said.
Four factors
Berendt cited a case-controlled study from the Mayo Clinic in Rochester, Minn., that identified, through multivariate analysis, four key preoperative risk factors for deep infection. The factors include the following:
- superficial infection;
- a history of cancer;
- a history of prior joint replacement surgery; and
- any lengthy surgical procedures in patients with comorbidities.
He described superficial infection as a major factor. The others increased the infection risk from one and a half to three times.
Purulence is another sign of possible infection an orthopedist might encounter during a hip revision. But in only about 10% of cases is late time to revision associated with infection, Berendt said. “The majority of infected implants will be failing early.�
Despite the number of tests to diagnose these infections, most of them provide only limited information and some of the better ones, like arthrograms, blood workups and isotope scans, do not reliably detect chronic infection.
“We make a lot of use instead of intraoperative and postoperative tests like frozen sections and cultures taken at the time of surgery,� Berendt said. And if a case does not appear obviously infected, the multiple culturing technique he uses, combined with histology, will usually determine if it is.
This approach unequivocally demonstrates whether there is acute inflammation present, which is “the hallmark of infection,� he said.
In the OR, orthopedic surgeons should meticulously take samples of the sinuses and the tissue surrounding the joints they suspect of being loose or failing from infection.
“What clinicians need to do is to get some [perspective] about the probability of infection before they start, and then use a rigorous protocol for sampling around the implant and looking at histological appearances as well,� he said.
For more information:
- Berendt A. Symposium: Infection in total hip replacement: the battle with MRSE and MRSA — Diagnosis dilemmas. Presented at the British Orthopaedic Association Annual Congress. Sept. 20-23, 2005. Birmingham, England.