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.
|Buckling||A complete collapse of the knee, often secondary to pain or muscle weakness of the quadriceps.3|
|Effusion||Fluid accumulation in the knee joint causing swelling.|
|Giving way||Symptom 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 claudication||An 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.|
|Locking||When 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 value||Probability 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 value||Probability that an individual is affected with the condition when a positive test result (or clinical finding) is observed.|
|Pseudolocking||Occurs with arthritis, when the adjacent rough articular surfaces stick momentarily as they glide over one another.3|
|Possible Causes||Prevalence Among Patients Presenting to Primary Care Setting1|
|Knee pain||Unclassified strains/sprains||42%|
|Anatomic location of the pain|
|Anterior knee||Patellofemoral syndrome|
|Quadriceps femoris strain|
|Posterior knee||Hamstring strain|
|Bursitis (semimembranous, popliteal, gastrocnemius)|
|Deep venous thrombosis|
|Medial meniscal tear|
|Medial collateral ligament sprain|
|Hamstring (semimembranous) strain|