Frequently Asked Questions

The surgeon who did my hip replacement thinks I may have an infection in that joint. I'm searching the Internet for any information I can find that will help me navigate this situation. I'd like to be able to ask good questions and seek top notch care. What can you tell me to help me get ready for my next appointment with the surgeon?

Diagnosis of joint implant infections after hip replacement can be difficult. The bacteria can hide in many nooks and crannies of the joint. Efforts have been made to provide surgeons with guidelines to aid in the diagnosis of periprosthetic (around the joint) infections. In fact, in 2010 the American Academy of Orthopaedic Surgeons (AAOS) published what they call Clinical Practice Guidelines (CPGs) for the diagnosis of such infections. Here's a quick summary of the 15 guidelines. This information should give you a spring board for talking with your surgeon. Anyone suspected of a periprosthetic joint infection (PJI) should be screened using two tests: erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP).

  • Patients with higher lab values indicating inflammation (e.g., ESR and CRP tests) are more likely to have an infection. Further testing is required. This is based on a probability and statistics model.
  • One other lab test (i.e., gram stain) should not be used to say there is no joint infection. In other words, the gram stain test is not a good rule-out test.
  • Whenever ESR and CRP tests are abnormal, fluid should be aspirated (drawn) from the joint and sent for testing to confirm infection and type of pathogen (bacteria).
  • Aspiration is not necessary when there are normal ESR and CRP levels. Hip aspiration can be painful and difficult to do without actually injecting the joint with more bacteria. Therefore hip aspiration is not done routinely (unless there are abnormal screening tests) and especially not when surgery isn't going to be done.
  • Positive ESR and CRP tests in patients who are NOT having surgery should be retested in three months.
  • Taking fluid from the joint to test it for the specific bacteria present should be done before any antibiotics are given. Sometimes this doesn't happen and the patient is put on antibiotics immediately regardless of what kind of pathogen is present.
  • If antibiotics have been prescribed, then joint culture by aspiration must wait until two weeks after the patient stops taking the drugs. Discontinuing the medication is important because taking antibiotics limits the number of bacteria present and prevents accurate testing.
  • The need for diagnostic imaging (PET scans, bone imaging, CT scans, MRIs) is unclear. Patients who are not going to have surgery probably don't need the added testing.
  • When surgery is done, fluid should be taken from the joint and retested. In fact, more than one sample should be drawn and tested. More than one positive test increases the certainty that there is a joint infection. Every patient is unique and must be treated with consideration of all factors present. There isn't a one-size fits all kind of approach for a problem like this. The current guidelines outlined here are not set in stone or indefinite. As new studies are published, these guidelines may become outdated and will be revised and updated. For now, they are the most current guidelines we can offer you in your desire for useful information. Good luck!

    Craig Della Valle, MD, et al. Diagnosis of Periprosthetic Joint Infections of the Hip and Knee. In Journal of the American Academy of Orthopaedic Surgeons. December 2010. Vol. 18. No. 12. Pp. 760-770.

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