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Case Scenario 1

A 42-year-old man comes to your office for evaluation of a painful right knee. He reports that he awoke 3 days ago with pain and swelling in the affected knee. The previous day, he had been cleaning out a friend's garage.

  • Are there any alarm symptoms or features?
  • Which questions help the clinician narrow the differential diagnosis?
  • Does the patient require urgent evaluation by an orthopedic surgeon?

Knee pain is common, affecting 10% to 15% of adults at some point in their lifetime. Knee pain accounts for 3% to 5% of physician visits, or 33 million new visits per year.1,2 Precise anatomic location of the initial pain is key to making the diagnosis. A differential diagnosis can be formulated by considering the local anatomic structures. A thorough history and relevant physical examination should establish the etiology of the knee pain in most cases.

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BucklingA complete collapse of the knee, often secondary to pain or muscle weakness of the quadriceps.3
EffusionFluid accumulation in the knee joint causing swelling.
Giving waySymptom usually associated with ligamentous injuries.4 Occurs with normal walking but may be most prominent during pivoting movements, such as quick changes in direction. Results from a bony structure sliding on another in an abnormal way.
Intermittent claudicationAn aching, crampy, sometimes burning pain in the legs that typically occurs with walking and goes away with rest.
Likelihood ratio (LR)Incorporates both the sensitivity and specificity of a test (or clinical finding), providing a direct estimate of how much a test result will change the odds of having a disease.
LockingWhen the knee becomes stuck, usually in 45 degrees of flexion, and patient is unable to unlock the knee without manipulating it in some fashion.3
Negative predictive valueProbability that an individual is not affected with the condition when a negative test result is observed.
Odds ratio (OR)Ratio of the odds of an event occurring in the exposed group versus the unexposed group.
Positive predictive valueProbability that an individual is affected with the condition when a positive test result (or clinical finding) is observed.
PseudolockingOccurs with arthritis, when the adjacent rough articular surfaces stick momentarily as they glide over one another.3
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Possible CausesPrevalence Among Patients Presenting to Primary Care Setting1
Knee painUnclassified strains/sprains42%
Osteoarthritis34%
Meniscal tear9%
Collateral ligament7%
Cruciate ligament4%
Gout2%
Fracture1.2%
Rheumatoid arthritis0.5%
Infectious arthritis0.3%
Pseudogout0.2%
Anatomic location of the pain
Anterior kneePatellofemoral syndrome
Prepatellar bursitis
Patellar fracture
Patellar tendinitis
Quadriceps femoris strain
Osteoarthritis
Posterior kneeHamstring strain
Bursitis (semimembranous, popliteal, gastrocnemius)
Baker cyst
Deep venous thrombosis
Popliteal aneurysm
Medial kneeOsteoarthritis
Medial meniscal tear
Medial collateral ligament sprain
Anserine bursitis
Hamstring ...

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