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NBME 20 Answers

nbme20/Block 2/Question#20

A 19-year-old man who is a college student is ...

Subcutaneous crepitus

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submitted by strugglebus(89),

Bronchophony= pneumonia Expiratory stridor= tracheobronchial obstruction (mass/foreign body) Inspiratory stridor = laryngeal obstruction Succussion splash= test for pyloric stenosis

When there is a fractured rib it will cause a trauma pnemothorax which can cause air to escape and become trapped under the skin leading to crepitus.

charcot_bouchard  Actually when a fractured rib puncture lung then it cause sc emphysema. +  
mbourne  "Chest trauma, a major cause of subcutaneous emphysema, can cause air to enter the skin of the chest wall from the neck or lung. When the pleural membranes are punctured, as occurs in penetrating trauma of the chest, air may travel from the lung to the muscles and subcutaneous tissue of the chest wall. When the alveoli of the lung are ruptured, as occurs in pulmonary laceration, air may travel beneath the visceral pleura (the membrane lining the lung), to the hilum of the lung, up to the trachea, to the neck and then to the chest wall. The condition may also occur when a fractured rib punctures a lung; in fact, 27% of patients who have rib fractures also have subcutaneous emphysema. Rib fractures may tear the parietal pleura, the membrane lining the inside of chest wall, allowing air to escape into the subcutaneous tissues." +  

 +0  upvote downvote
submitted by monoloco(80),

I have regarded crepitus as the rubbing of bone-on-bone. My study partner and I think this is a purely definitional question. Yes, crepitus could also be trapped air. Context, I guess.

medstudent65  Crepitus is used to describe bone-on-bone grinding. Subcutaneous crepitus is very specific sound referencing air finding its way into the skin which you can hear but also feel by rubbing your hand over the affected area. The addition of subcutaneous lets you know we are specifically talking about air in the skin. +1  

 +0  upvote downvote
submitted by rio19111(6),

Diagnosis: Pneumomediastinum (FA 2019, 659)

+Hamman Sign=Crepitus on cardiac auscultation

Etiology: spontaneous (due to rupture of pulmonary bleb) or 2° (eg, trauma, iatrogenic, Boerhaave syndrome).

md_caffeiner  also look on FA 667 traumatic pnx where it says "rib fracture" +