Clinical History
A 49-year-old woman with a past medical history of encephalopathy presented at the emergency department after an epileptic seizure with bilateral shoulder pain and decreased range of motion.
Imaging Findings
The radiographic study (Fig. 1) showed a rounded appearance of both humeral heads, as a result of internal rotation, forming the lightbulb sign. A bone defect on the medial side of each humeral head consistent with fracture and fragmentation was also evident.
On CT (Fig. 2), apart from the posterior position of the humeral heads to glenoid, an impaction fracture of the anteromedial aspect of both humeral heads was obvious. Bone fractures, involving the lesser tubercles, and fragmentation were also confirmed. There were no bone glenoid lesions.
Imaging findings were compatible with a bilateral posterior shoulder fracture-dislocation, with reverse Hill-Sachs lesion. The patient was surgically treated with a bilateral McLaughlin procedure.
Discussion
Posterior shoulder dislocations account for only 2-4% of all shoulder dislocations and often occur as a consequence of a direct trauma, epileptic crisis or electrocution. In these two last conditions, bilateral dislocations are not infrequent, as a result of a more powerful contraction of internal rotator muscles during seizure, which leads to a more superior and posterior position of the humeral heads. Associated humeral head and glenoid lesions can occur due to continuous pressure between these structures [1-5].
Clinically, patients usually present with shoulder pain on a fixed internally rotated position. On physical examination there is a limited range of shoulder motion, mostly to external rotation and abduction [2].
Imaging findings on a frontal shoulder radiograph include loss of overlap between the humeral head and the glenoid, and an internally rotated humeral head, resulting in a rounded appearance that creates the lightbulb sign. Although findings on axillary view are usually obvious, this is rarely obtained because patients complain about pain to motion, as in our case [1].
While posterior shoulder dislocation can be difficult to diagnose clinically, as well as on radiographs, CT is often used to confirm the posterior position of the humeral head to the glenoid, as well as associated injuries such as fractures. Reverse Hill-Sachs lesion is an impaction fracture of the anteromedial humeral head, and it can be of surgical importance to identify and correct it, in order to prevent avascular necrosis. Usually, if the defect involves more than 25% of the humeral head, a surgical approach is preferred, as in the current case. Another complication, also present in this case, is a fracture involving the lesser tubercle which is anatomically related to the insertion site of the internal rotation of the shoulder [1,2,5].
Posterior shoulder dislocation is the most commonly missed major joint dislocation, frequently resulting in a delayed diagnosis that may result in shoulder instability, osteoarthritis and avascular necrosis [1,4,5]. Our case highlights the importance of a high level of suspicion for this diagnosis after a seizure. Follow-up of the case was lost after patient discharge.
Differential Diagnosis List
Bilateral posterior shoulder dislocation with reverse Hill-Sachs lesion.
Shoulder pseudodislocation
Rotator cuff injury
Final Diagnosis
Bilateral posterior shoulder dislocation with reverse Hill-Sachs lesion.
