Anatomy for MRCEM primary exam

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Upper limb Anatomy

Infraspinatus muscle

Actions and innervation of: Infraspinatus

Knowledge of origins and insertions NOT required

Knowledge of the muscles which exert group effects (eg abduction) at the shoulder joint and the means of clinical testing: an ability to describe shoulder movements according to muscle actions and an appreciation of the role of humeral & scapular rotation

OriginInfraspinous fossa (Below the spine on Scapula)
InsertionGreater tubercle of the Humerus (Just below Supraspinatus)
Nerve supplySuprascapular nerve
ActionsLateral rotation of the arm

Though the curriculum says origin and insertion not required, we’ve included them as that knowledge will help you understand the movements better based on muscle orientation.

Supraspinatus and Infraspiantus Origin and Insertions – Image modified from BodyParts3D, © The Database Center for Life Science licensed under CC Attribution-Share Alike 2.1 Japan

As the name suggests, it originates from Infra (below) spinous fossa, located on the posterior aspect of Scapula. It goes behind the humeral head and inserts on to the greater tubercle of Humerus on the lateral side, just below the insertion of Supraspinatus. When the muscle contracts, it’ll pull the humeral head back and arm gets rotated laterally.

Testing the Infraspinatus

While the patient stands with the elbow flexed to 90 degrees and pointing anteriorly. The therapist applies a medially directed force to the arm. The patient is asked to resist the force.
If the patient experiences pain or weakness, the test is considered Positive.