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[Dr. Handy] Hi, welcome to Harrison's Podclass, where we discuss important concepts in internal medicine. I'm Cathy Handy. [Dr. Wiener] And I'm Charlie Wiener, and we're coming to you from the Johns Hopkins School of Medicine. [Dr. Handy] Welcome to today's episode, a 67-year-old with a painful right knee.
[Dr. Wiener] Hey Cathy, well today's case is a 67-year-old woman with a history of right knee replacement four years prior, who presents with one month of worsening right knee pain and decreased range of motion in that knee. On examination, she's afebrile but her right knee is warm and red with some pustules over the top. The redness has a distinct border and surrounds the knee. That knee is tender to direct pressure and movement. The left knee is normal.
[Dr. Handy] Okay, so let's stop there for a minute and talk about what we heard so far. So, it sounds like she has some inflammation of the knee with warmth and tenderness, and it's notable that in the knee is a foreign body, her knee replacement that you mentioned she had. So far, you've only told me about this one joint being involved, so I would be thinking of causes of acute monoarticular arthritis.
Now, infection or septic arthritis would be on the list, but you also need to think about crystalline arthritis and hemarthrosis, especially in patients with a prior history of bleeding disorders. Other things to think about would be trauma, and then less commonly, autoimmune diseases. [Dr. Wiener] You mentioned infection, I presume you're worried about the prosthetic joint. Wouldn't that be surprising given the time course, since her surgery was years ago?
[Dr. Handy] So it still could be possible, her symptoms and examination are consistent with what we call chronic periprosthetic joint infection. So that's traditionally classified as early which would be within three months after implementation; delayed which is between three months and two years after surgery; or late which would be over two years after implantation.
For therapeutic decision making, it's more useful to classify periprosthetic joint infection as either acute hematogenous with fewer than three weeks of symptoms; early post interventional infections manifesting within one month after surgery; or chronic periprosthetic joint infection with symptoms that last for longer than three weeks. [Dr. Wiener] Okay, so the fact that she's presenting with about one month of symptoms four years after her knee replacement is not atypical.
What are the typical findings of a chronic infection? [Dr. Handy] Key findings are joint effusion, local pain, implant loosening, and occasionally a sinus tract. Now the patient may have generalized fatigue from the low-grade inflammation. Tell me more about her history and if she has any other joint problems.
[Dr. Wiener] Okay, so as far as past history is, she was a former competitive skier and had injured that knee many times through her twenties and thirties, her knee replacement was for DJD. She's remarkably healthy otherwise. The left knee has some [unintelligible] DJD and is being followed, but as I mentioned is not acutely inflamed today. Her only medication is atorvastatin for hyperlipidemia. I'll also say that outside of the right knee her physical examination is totally normal.
We did get some labs and her white count is 14.5 with 80% neutrophils. Her C-reactive protein is elevated at 13 mg/L, and she had a sed rate that's elevated at 50 mm/hour. [Dr. Handy] So she has a neutrophil predominant leukocytosis with an elevation of her CRP and ESR, and these values can be seen in chronic joint infections, although they are relatively sensitive at this level with a CRP that's at least 10 and an ESR of at least 30, they're not specific for this.
[Dr. Wiener] Okay, well let's get to the question. The question reads, which of the following should you request? And the options are A. initiate IV vancomycin; B. a joint aspiration; C. a surgical consultation; and then option D says, you can get A and C, which would be vancomycin and a surgical consultation; or option E says, you can get B and C, which is joint aspiration and a surgical consultation.
[Dr. Handy] Well, what I would do is definitely joint aspiration, but then also surgical consultation, so that would be option choice E. Now an important distinction is that she does not appear septic, so in this case empiric antibiotics are not warranted. Antibiotics should be deferred until joint aspiration or surgical sampling can be performed.
Now, treatment of prosthetic joint infection requires a multidisciplinary approach, including an orthopedic surgeon and an infectious disease specialist, so most patients are referred to a specialized center. In general, the goal of treatment is cure, so that means a pain-free, functional joint with complete eradication of the infecting pathogens. As a rule, antimicrobial therapy without surgical intervention is not curative but merely suppressive. There are four curative surgical options.
So either debridement and implant retention, a one-stage implant exchange, a two-stage implant exchange, or an implant removal without replacement. [Dr. Wiener] What are the common causative organisms in chronic prosthetic joint infections? [Dr. Handy] It's most commonly caused by low-virulence organisms, such as coagulase-negative staphylococci or P. acnes. The more acute forms are typically due to the more virulent bacteria such as Staph aureus.
[Dr. Wiener] Okay, great. So the teaching points in this case are that prosthetic joint infections should be characterized by their timeframe. Chronic infections may happen even years after surgery and usually present with low grade systemic inflammation and findings that are local to the prosthesis. Appropriate therapy is multidisciplinary and empiric antibiotics are not necessary in a non-acutely ill, non-septic patient.
[Dr. Handy] And you can read more about this in Harrison's chapter on infections of prosthetic joints. [Dr. Wiener] I'm glad to know there's a full chapter on that. [Dr. Handy chuckles] [outro music] [Mr. Shanahan] This is Jim Shanahan, publisher at McGraw Hill. Harrison's Podclass is brought to you by McGraw Hill's Access Medicine, the online medical resource that delivers the latest trusted content from the best minds in medicine. Go to accessmedicine.com to learn more.