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Difficulty: MediumPhysical Examination Findings

A 62-year-old woman presents to the urgent care clinic with sudden-onset, severe right posterior calf pain that began while she was walking her dog in a park. The pain was followed rapidly by diffuse swelling of the lower leg. She has a history of advanced osteoarthritis in both knees and hypertension. Her current medications include amlodipine and as-needed ibuprofen. Vital signs are within normal limits. On physical examination, the right calf is visibly swollen, tense, and diffusely tender to palpation. The physician suspects a ruptured popliteal (Baker) cyst but wants to clinically differentiate this condition from an acute deep vein thrombosis prior to ordering ultrasonography. Which of the following physical examination findings is most specific for confirming a ruptured popliteal cyst in this patient?

  1. A crescent-shaped area of ecchymosis located distal to the medial malleolusAnswer
  2. B
    Sharp calf pain elicited by abrupt, passive dorsiflexion of the ankle
  3. C
    A palpable, focal, and pulsatile swelling localized within the popliteal fossa
  4. D
    Diffuse pitting edema extending continuously from the dorsum of the foot to the mid-calf
  5. E
    A palpable, tender, cord-like structure tracking along the medial aspect of the thigh

Answer

A crescent-shaped area of ecchymosis located distal to the medial malleolus
The correct answer describes the Crescent sign. A popliteal (Baker) cyst is a fluid-filled sac resulting from the herniation of the synovial membrane, most commonly associated with underlying knee pathology such as osteoarthritis or rheumatoid arthritis. When the cyst ruptures, the inflammatory synovial fluid dissects inferiorly along the fascial planes of the calf. Gravity causes this fluid and associated minor hemorrhage to pool distally, manifesting as a crescent-shaped area of bruising (ecchymosis) just below the medial malleolus. This physical examination finding is highly specific for a ruptured popliteal cyst and helps distinguish it clinically from a deep vein thrombosis (DVT).

Step-by-Step Solution

1
Evaluate the patient's clinical presentation and risk factors.
The patient has sudden calf pain and swelling with a history of knee osteoarthritis, which strongly points toward either an acute deep vein thrombosis (DVT) or a ruptured popliteal (Baker) cyst.
Sudden calf pain in the setting of osteoarthritis is the classic presentation of a ruptured cyst, but DVT must always be excluded due to high morbidity.
2
Identify physical examination findings that differentiate the two primary conditions.
While swelling and tenderness are common to both, a tracking hematoma pooling dependently at the ankle is specific to synovial fluid extravasation.
When a popliteal cyst ruptures, the inflammatory synovial fluid leaks between the muscles of the calf (often the medial head of the gastrocnemius) and tracks inferiorly, resulting in a characteristic bruise.
3
Select the option describing this pathognomonic sign.
The correct physical finding is the Crescent sign (ecchymosis distal to the medial malleolus).
This is a highly specific dermatologic manifestation that confirms the mechanical rupture and gravitational tracking of the cyst fluid, ruling against an intravascular clot like a DVT.

Key Concept

The Crescent sign (ecchymosis below the medial malleolus) is a specific physical examination finding that differentiates a ruptured popliteal (Baker) cyst from an acute deep vein thrombosis.
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Physical Examination Findings

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