Case

A 22yo is injured while ice climbing and landing on the point of an ice pick. The pick penetrated the posterior aspect of their shoulder. The injury caused a small amount of bleeding that was managed at the local hospital. It is now 24 hours later and the patient is able to abduct their arm ~10-15 degrees, but is unable to abduct any further. They are able to flex and extend as well as shrug their shoulders.

Question 1/3 - Which muscle is most likely dysfunctional in this patient?

Click on your selected option(s) below  (correct = 2, over-thinking = 3+)

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Incorrect. The biceps brachii primary actions are flexion (glenohumeral as well as elbow joints) and supination.

Incorrect. The triceps brachii primary actions are extension (glenohumeral as well as elbow joints).   

Incorrect.  While supraspinatus has abduction action, this is limited to about 15 degrees. The patient history indicates they are able to move 10-15 degrees consistent with a functional supraspinatus.

Correct! The deltoid has functions of abduction, flexion, and extension at the glenohumeral joint. There are other muscles that can flex/extend the glenohumeral joint so the patient is able to make those motions. However, this is the only muscle able to abduct past 15 degrees which the patient is unable to perform, so this muscle is dysfunctional. 

Incorrect. The trapezius attaches along the scapula and clavicle, so it has no action at the glenohumeral joint.  The case history indicates the patient can shrug their shoulder indicating that trapezius is functional.

 Movement of the scapula does engage to raise the arm past the shoulder, but this is an action rotating the scapula not an action on the humerus.

Incorrect. Infraspinatus is part of the rotator cuff muscles responsible for external rotation (along withe teres minor).

Incorrect.  The coracobrachialis muscle is involved in flexion at the glenohumeral joint (one of several muscles that act as flexors, for example biceps brachii and the deltoid also have flexion roles at the glenohumeral joint).