WBR1492

Author	PageAuthor::William J Gibson
Exam Type	ExamType::Surgery Shelf
Main Category	MainCategory::Orthopedics
Sub Category	SubCategory::Diagnosis
Prompt	[[Prompt::A 24 year old man presents to the emergency room after his car rear-ended another at approximately 15 mph. He was driving back after pitching at his baseball game when the crash occurred, but he cannot remember the crash itself. Physical exam reveals an internally rotated shoulder, with positive Jerk test, consistent with posterior shoulder dislocation. What is the most likely cause of this patient's shoulder injury?]]
Answer A	AnswerA::Injury from throwing the baseball
Answer A Explanation	[[AnswerAExp::Throwing injuries place large amounts of stress on the posterior aspects of the should. Throwing most often injures the muscles of the rotator cuff and would result in an anterior shoulder dislocation rather than a posterior shoulder dislocation.]]
Answer B	AnswerB::Whiplash
Answer B Explanation	AnswerBExp::While whiplash is a common injury in motor vehicle accidents, whiplash would not be responsible for a posterior surgical dislocation. Whiplash would typically result in injuries to the cervical spine rather than the shoulder.
Answer C	AnswerC::Airbag injury
Answer C Explanation	[[AnswerCExp::Airbags often cause abrasions or contusions of the arms, face and chest. The collision in this vignette was a fairly low velocity collision, making the likelihood that the airbag would cause substantial harm smaller. It would be highly unlikely that an airbag would cause a posterior shoulder dislocation, especially given the speed of the collision.]]
Answer D	AnswerD::Seatbelt injury
Answer D Explanation	[[AnswerDExp::Patients with injuries from seat belts often carry the "seat belt sign", a triangle of skin abrasions covering the neck chest and abdomen. The car was likely traveling too slowly (15 mph) for a seatbelt collision to be a reasonable source of the shoulder injury in this patient.]]
Answer E	AnswerE::Seizure
Answer E Explanation	[[AnswerEExp::Seizure can cause posterior shoulder dislocation when tetanic contractions of the external shoulder rotators (teres major, subscapularis, latissimus dorsi, and pectoralis major) overpower the internal rotators (teres minor and infraspinatus). This causes the head of the humerus to be pulled posteriorly out of the glenoid fossa.]]
Right Answer	RightAnswer::E
Explanation	[[Explanation::This patient most likely suffered a posterior shoulder dislocation as a result of his seizure. Posterior shoulder dislocations are rare (<5%). In most shoulder dislocations, the humerus is displaced anteriorly (>95%). Seizure can cause posterior shoulder dislocation when tetanic contractions of the external shoulder rotators (teres major, subscapularis, latissimus dorsi, and pectoralis major) overpower the internal rotators (teres minor and infraspinatus). This causes the head of the humerus to be pulled posteriorly out of the glenoid fossa. If a bilateral posterior shoulder dislocation is encountered, this almost always indicates injury due to a seizure. Approximately 15% of posterior shoulder dislocations are bilateral. In most cases, posterior shoulder dislocation can be corrected by closed reduction using the Depalma method (not high yield for Shelf exam). However, when diagnosis is delayed closed reduction under general anesthesia may be necessary. The joint should be immobilized for 4 weeks following reduction. Educational Objective: Posterior shoulder dislocation may be caused by seizures or electrocution. During these events, tetanic contraction of the external rotators of the shoulder can pull the humerus posteriorly out of the glenoid fossa. References: Perron AD, Jones RL. Posterior shoulder dislocation: avoiding a missed diagnosis. Am J Emerg Med. 2000;18(2):189-91. Wallis LA, Greaves I. Injuries associated with airbag deployment. Emerg Med J. 2002;19(6):490-3. Betz ME, Traub SJ. Bilateral posterior shoulder dislocations following seizure. Intern Emerg Med. 2007;2(1):63-5.]]
Approved	Approved::Yes
Keyword	WBRKeyword::Ortho, WBRKeyword::Orthopedics, WBRKeyword::Shoulder, WBRKeyword::Shoulder dislocation, WBRKeyword::Posterior shoulder dislocation, WBRKeyword::Seizure
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::