College of Massage Therapists of British Columbia (CMTBC) Practice Exam

Which movement is likely to cause a subcoracoid dislocation?

1. Excessive flexion

2. Excessive internal rotation

3. Excessive horizontal adduction

4. Excessive external rotation and abduction

The correct answer is: Excessive external rotation and abduction

A subcoracoid dislocation occurs when the humeral head moves beneath the coracoid process of the scapula, leading to a specific type of shoulder dislocation. This type of dislocation is most commonly associated with movements that stretch or destabilize the shoulder joint. In this case, excessive external rotation and abduction is the movement most likely to cause a subcoracoid dislocation. When the shoulder is abducted and externally rotated, there is increased tension on the anterior structures of the shoulder, including the capsule and the ligaments. This position creates a risk for the humeral head to slip out of the joint, particularly in conditions where external forces are applied, such as during sports or high-energy activities. Understanding shoulder mechanics is vital; when the arm is in this abducted and externally rotated position, the risk of dislocating the humeral head forward and downward increases significantly due to the nature of shoulder stabilization which is primarily dependent on the interaction between the labrum, ligaments, and the rotator cuff muscles. This vulnerability is what makes excessive external rotation and abduction the primary movement responsible for subcoracoid dislocations.