Daily answer

[Scott Rand]

1.        What muscles are involved in Shoulder abduction?

Action:  Shoulder abduction

Nerves:  Suprascapular, axillary, CN XI (spinal accessory), and long thoracic

Skeletal muscles:  Supraspinatus, deltoid, trapezius, and serratus anterior

Cutaneous distribution:  None except for the axillary nerve

Neuromuscular deficit:  Weakness/paralysis when abducting at the shoulder under resistance. In normal subjects the supraspinatus initiates the first 15 degrees of abduction along the vertical plane. The deltoid functions from 15 to 90 degrees, while synergistic actions of the trapezius and serratus anterior abduct from 90 to 180 degrees by rotating the scapula laterally. Denervation is accompanied by muscular atrophy, shoulder adduction, ‘winged’ scapula, and cutaneous deficit along the distribution of the axillary (superior lateral brachial cutaneous) nerve.

Differential diagnosis:  Abductor weakness/paralysis plus cutaneous deficit along the superior and lateral arm are diagnostic of axillary nerve impairment. A “winged” scapula indicates a deficit of the serratus anterior/long thoracic nerve.

 

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Scott E Rand, MD  FAAFP CAQSM

Director, Primary Care Sports Medicine Fellowship

Co Director of Sports Medicine, Houston Methodist Orthopedics and Sports Medicine Willowbrook

Assistant Professor of Clinical Family Medicine  Houston Methodist Academic Institute

Adjunct Assistant Professor of Family and Community Medicine, Texas A&M University

Assistant Professor of Family Medicine in Clinical Medicine  Weill Cornell Medical College.

13802 Centerfield Dr  Suite 300

Houston, TX  77070

[Scott Rand]

The most common nerve injury in glenohumeral shoulder dislocations is the:

A.      Suprascapular nerve

B.      Axillary nerve

C.      Long thoracic nerve

D.      Radial nerve

E.       Musculocutaneous nerve

 

Correct: B

The suprascapular nerve innervates the supra and infra spinatus muscles; injury is produced by stretching or compression, not dislocation.

The axillary nerve is the most common nerve injured by shoulder dislocation.

The long thoracic nerve is usually injured by a direct blow or compression which leads to paresis of the serratus anterior and scapular winging. The radial nerve - this nerve can be compressed at multiple sites along its course; even at the high axillary location it is not typically injured during shoulder dislocation. While injury to the musculocutaneous nerve due to dislocated shoulder is reported it is uncommon; more common is compression with excessive resistive elbow extension such as in bench press or pushups.

 

1.       Hodge DK, Safran MR. Sideline management of common dislocations. Curr Sports Med Rep. 2002, I:149-155