HLTH1008 Chap.10 Shoulder Complex, Axilla and Brachial Plexus
Shoulder Complex, Axilla and Brachial Plexus
The shoulder trades stability for range. This chapter begins with an anteroinferior dislocation that injures the axillary nerve, then describes the four joints of the shoulder complex, the static and dynamic stabilisers of the glenohumeral joint and the named labral tears.
It sets out the rotator cuff muscles with their nerves and insertions, the scapulohumeral rhythm and the coracoacromial arch, then builds the brachial plexus from roots to branches and explains upper and lower plexus palsies, scapular winging and the axilla. Plexus injuries are explained by the trunk that is stretched, which predicts the posture of the limb.
The axilla is described last as the space through which the plexus and vessels reach the limb.
What this chapter covers
- 01
Sternoclavicular and acromioclavicular joints
- 02
Scapulothoracic movement
- 03
Glenohumeral stability and labral tears
- 04
Rotator cuff and impingement
- 05
Scapulohumeral rhythm
- 06
Anteroinferior dislocation and the axillary nerve
- 07
Formation of the brachial plexus
- 08
Erb-Duchenne and Klumpke palsies
Worked example · free
Linking a weak movement to a cuff muscle and nerve
- +1Starting abduction from the side is the role the course gives supraspinatus, initiating abduction to about 15°.
- +1Once the arm is lifted, deltoid can carry abduction on, so the deficit is limited to the start.
- +1Supraspinatus inserts on the superior facet of the greater tubercle.
- +1It is supplied by the suprascapular nerve, C5 and C6.
Key terms
- Glenohumeral joint
- The multiaxial ball and socket joint between the humeral head and the glenoid.
- Bankart lesion
- A tear of the anterior and inferior glenoid labrum after dislocation.
- Scapulohumeral rhythm
- The roughly two to one ratio of glenohumeral to scapular movement in elevation.
- Coracoacromial arch
- The acromion, coracoid and coracoacromial ligament above the humeral head.
- Axillary nerve
- The nerve that winds around the surgical neck and supplies deltoid and teres minor.
- Long thoracic nerve
- The nerve from C5 to C7 that supplies serratus anterior.
- Erb-Duchenne palsy
- Injury to the superior trunk of the brachial plexus, C5 and C6.
- Klumpke palsy
- Injury to the inferior trunk of the brachial plexus, C8 and T1.
- Supraspinatus
- The rotator cuff muscle that initiates abduction and is most often involved in impingement.
Shoulder Complex, Axilla and Brachial Plexus FAQ
Why does the shoulder usually dislocate anteroinferiorly?
The anterior and inferior parts of the glenohumeral capsule are its weakest, and the humeral head sits on a shallow glenoid that relies on soft tissue for stability. The lecture lists the capsule, labrum, ligaments, nerves and vessels as structures at risk when the head is driven forward and down.
How is the brachial plexus formed?
Ventral rami of C5 to C8 and T1 form the roots, which pass between scalenus anterior and medius, unite into trunks above the clavicle, split into anterior and posterior divisions below it and regroup as cords around the axillary artery. The course counts four supraclavicular and thirteen infraclavicular branches.
What causes winging of the scapula?
Injury to the long thoracic nerve, from C5 to C7, which supplies serratus anterior. That muscle normally holds the medial border of the scapula against the chest wall while protracting and rotating it, so its paralysis lets the border lift away when the patient pushes forward.
What is the scapulohumeral rhythm?
When the arm is raised to 180°, about 120° occurs at the glenohumeral joint and about 60° from rotation of the scapula, a ratio of roughly 2:1. The rhythm spreads movement over several joints, keeps the glenoid under the humeral head and keeps muscles at a good working length.
Which muscles form the rotator cuff?
Supraspinatus, infraspinatus, teres minor and subscapularis. Supraspinatus initiates abduction, infraspinatus and teres minor rotate the arm laterally, subscapularis rotates it medially, and together they hold the humeral head in the shallow glenoid while larger muscles move the arm.
Exam move
Draw the four shoulder joints on one diagram and write a movement and a ligament for each. Learn the rotator cuff as a four-row table of muscle, nerve, insertion and action. Then draw the plexus as five stacked stages from roots to branches and add the lesions: Erb-Duchenne at the superior trunk, Klumpke at the inferior trunk, the axillary nerve at the surgical neck and the long thoracic nerve at serratus anterior.
Practise the dislocation case aloud, naming the weak capsule, the nerve at risk and the muscles and skin it supplies, then repeat for Erb-Duchenne palsy and scapular winging.
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