Shoulder joint and rotator cuff
Axilla, scapular muscles, shoulder joint and rotator cuff: FCPS anatomy
Axilla, pectoral region, scapular muscles, shoulder joint and rotator cuff for FCPS Part 1, built around nerve injuries and dislocations. Covers axillary artery parts, node levels, quadrangular and triangular spaces, suprascapular entrapment, winging, painful arc and frozen shoulder.
One of the most tested topics in past papers
Walls and contents of the axilla
The axilla is a pyramid-shaped passage between the arm and the chest wall. Its contents are the axillary artery and vein, the cords and branches of the brachial plexus, axillary lymph nodes and fat. The artery and plexus are wrapped in the axillary sheath, a continuation of the prevertebral layer of deep cervical fascia drawn down from the neck.
| Wall | Formed by |
|---|---|
| Apex (cervicoaxillary canal) | Clavicle, outer border of first rib, upper border of scapula |
| Anterior | Pectoralis major, pectoralis minor, subclavius, clavipectoral fascia |
| Posterior | Subscapularis, teres major, latissimus dorsi |
| Medial | Upper ribs and intercostals covered by serratus anterior (long thoracic nerve on its surface) |
| Lateral | Intertubercular groove of the humerus (biceps tendon, coracobrachialis) |
| Floor (base) | Skin and axillary fascia, continuous with the pectoral and latissimus fascia |
Axillary artery
Begins at the outer border of the first rib and becomes the brachial artery at the lower border of teres major. Pectoralis minor crosses it and divides it into three parts, with one, two and three branches.
| Part | Branches |
|---|---|
| First (above pectoralis minor) | Superior thoracic |
| Second (behind pectoralis minor) | Thoracoacromial, lateral thoracic |
| Third (below pectoralis minor) | Subscapular (largest), anterior and posterior circumflex humeral |
The scapular anastomosis links the subclavian artery (suprascapular, dorsal scapular) with the third part of the axillary artery (circumflex scapular branch of subscapular). It keeps the limb alive if the artery is tied between the thyrocervical trunk and the subscapular artery.
Axillary lymph nodes
Five anatomical groups: anterior (pectoral) along the lateral thoracic vessels, posterior (subscapular), lateral (humeral), central and apical. All drain finally through the apical group into the subclavian trunk. Surgeons use levels defined by pectoralis minor:
| Level | Position | Groups |
|---|---|---|
| I | Lateral to (below) pectoralis minor | Anterior, posterior, lateral |
| II | Behind pectoralis minor | Central; interpectoral (Rotter) nodes between the pectoral muscles |
| III | Medial to (above) pectoralis minor | Apical |
The breast sends about 75% of its lymph to the axilla, first to the anterior (pectoral) group at level I, which is where the sentinel node usually lies.
Muscles of the scapula and pectoral region
- Medial border of the scapula receives levator scapulae, rhomboid minor and rhomboid major (dorsal scapular nerve) on its posterior lip and serratus anterior (long thoracic nerve) along its anterior (costal) surface.
- Serratus anterior holds the scapula against the chest wall and protracts and upwardly rotates it. Its paralysis (long thoracic nerve, axillary clearance) causes marked winging on pushing against a wall and inability to raise the arm fully above the head, although abduction to about 90° survives.
- Trapezius (spinal accessory nerve) elevates the shoulder tip (upper fibres raise the lateral clavicle), retracts and upwardly rotates the scapula. Injury during posterior triangle surgery causes a weak shrug, drooping shoulder, difficulty raising the arm overhead and milder winging.
- Pectoralis minor (medial pectoral nerve) depresses and protracts the scapula. Latissimus dorsi (thoracodorsal nerve) extends, adducts and medially rotates the arm; injury at mastectomy weakens all three.
- Above 90°, abduction continues only because trapezius and serratus anterior rotate the glenoid upwards: overall, humerus and scapula move in a ratio of about 2:1.
- Surface levels with the arms by the side: superior angle T2, root of the spine of the scapula T3, inferior angle T7.
Spaces behind the arm
| Space | Boundaries | Contents |
|---|---|---|
| Quadrangular | Teres minor above, teres major below, long head of triceps medially, surgical neck of humerus laterally | Axillary nerve, posterior circumflex humeral artery |
| Triangular (upper) | Teres minor above, teres major below, long head of triceps laterally | Circumflex scapular artery |
| Triangular interval (lower) | Teres major above, long head of triceps medially, shaft of humerus laterally | Radial nerve, profunda brachii artery |
A fracture of the surgical neck of the humerus or an anterior dislocation injures the axillary nerve: weak abduction beyond the first few degrees, and numbness over the lower deltoid (regimental badge area).
Suprascapular nerve entrapment
| Site | Muscles wasted | Typical patient |
|---|---|---|
| Suprascapular notch (under the superior transverse scapular ligament) | Supraspinatus and infraspinatus | Weightlifters, traction; weak initiation of abduction and lateral rotation |
| Spinoglenoid notch (at the lateral edge of the spine) | Infraspinatus only | Overhead athletes (volleyball), labral ganglion cyst |
- The nerve has no cutaneous branch, so skin sensation is normal; deltoid power is normal because the axillary nerve is separate.
- The suprascapular artery runs above the transverse ligament, so it escapes when the nerve is trapped below it.
Joints of the shoulder girdle
- Sternoclavicular joint: saddle-type synovial joint with an articular disc; the only bony link of the upper limb to the axial skeleton. Posterior dislocation can press on the trachea, oesophagus and great veins.
- Acromioclavicular joint: weak plane joint; vertical stability comes from the coracoclavicular ligament (conoid and trapezoid parts). In a severe AC separation the lateral clavicle appears to ride high because the coracoclavicular ligament is torn and the scapula and arm drop. This ligament also transmits the weight of the arm to the clavicle.
- Clavicle fracture: usually the middle third; the medial fragment is pulled up by sternocleidomastoid; the lateral fragment is pulled down by the weight of the arm and medially by pectoralis major.
Glenohumeral joint and dislocation
- A ball-and-socket joint with a shallow glenoid, deepened by the glenoid labrum. Stability depends mainly on the rotator cuff, which blends with the capsule above, in front and behind. The long head of biceps arises from the supraglenoid tubercle and runs inside the joint capsule.
- The inferior capsule has no rotator cuff support, and it is lax to allow abduction. A fall on an abducted, externally rotated arm levers the head out anteroinferiorly; over 95% of dislocations are anterior.
- Bankart lesion: detachment of the anteroinferior labrum and capsule from the glenoid; the main cause of recurrent dislocation in young people, each episode needing less force. Hill–Sachs lesion is the dent in the posterolateral humeral head.
- Over the age of 40, persistent weakness after dislocation is more often a rotator cuff tear than an axillary nerve palsy.
- Posterior dislocation follows seizures or electric shock; the arm is held medially rotated, external rotation is blocked, and the AP film shows a "light bulb" head. It is easily missed.
Rotator cuff
| Muscle | Action | Nerve | Insertion |
|---|---|---|---|
| Supraspinatus | Initiates abduction (first 15°), holds head in glenoid | Suprascapular | Greater tuberosity, superior facet |
| Infraspinatus | Lateral rotation | Suprascapular | Greater tuberosity, middle facet |
| Teres minor | Lateral rotation | Axillary | Greater tuberosity, inferior facet |
| Subscapularis | Medial rotation | Upper and lower subscapular | Lesser tuberosity |
- Abduction: supraspinatus starts it and steadies the head while deltoid (axillary nerve) carries it to 90°; trapezius and serratus anterior take it overhead.
- Painful arc (about 60–120°): in this range the inflamed supraspinatus tendon is squeezed under the acromion and coracoacromial ligament; above 120° it passes clear, so the pain eases. Good power suggests tendinopathy; marked weakness suggests a tear.
- Complete supraspinatus tear: cannot initiate abduction, but can hold the arm once it is passively raised (deltoid takes over).
- Frozen shoulder (adhesive capsulitis): inflammation then fibrosis and contraction of the capsule; active and passive movement equally reduced, external rotation most, normal X-ray. Commoner in diabetes. A missed posterior dislocation also blocks external rotation, so X-ray first.
Remember Supraspinatus begins abduction, deltoid continues it, and the scapular rotators finish it.
Exam trap Teres minor is the only cuff muscle supplied by the axillary nerve; the suprascapular nerve supplies supraspinatus and infraspinatus.
Exam trap Pectoralis minor, not major, divides the axillary artery into parts and defines node levels.
How FCPS asks about this
- Winged scapula, cannot raise arm overhead after axillary clearance: long thoracic nerve; serratus anterior protraction and upward rotation lost.
- Surgical neck fracture, weak abduction, numb lateral arm: axillary nerve in the quadrangular space; deltoid and teres minor.
- Wasting of infraspinatus only: spinoglenoid notch; both spinati wasted means suprascapular notch.
- Lateral boundary of the triangular interval: shaft of humerus; radial nerve and profunda brachii pass through.
- Lateral clavicle riding high after a fall on the shoulder: coracoclavicular ligament torn.
- Recurrent anterior dislocation in a young athlete: Bankart lesion; dislocation is anteroinferior because the inferior capsule lacks cuff support.
- Painful arc 60–120°: supraspinatus impinged under the acromion; diabetic with global loss of movement has frozen shoulder (capsular fibrosis).
Test yourself on this topic
5 of the 71 questions in our bank on this topic. Choose an answer to see why every option is right or wrong.
After axillary clearance, a woman can abduct her arm to about 90° but cannot raise it fully above her head, and her scapula wings when she pushes against a wall. Which action has been lost?
Answer: Protraction and upward rotation of scapula
Serratus anterior (long thoracic nerve, C5–C7) holds the medial border of the scapula against the chest wall, protracts it, and with trapezius rotates it upwards so the glenoid faces up. Above about 90° abduction depends on this scapular rotation, so overhead elevation fails and the scapula wings. The nerve runs on the medial wall of the axilla, on the surface of serratus anterior, where it is at risk in axillary dissection. Shrugging is upper trapezius and levator scapulae; adduction and medial rotation are latissimus dorsi and pectoralis major.
Serratus anterior
- Long thoracic nerve (C5–C7)
- Protracts and rotates the scapula upward
- Needed for overhead elevation
- On the medial axillary wall: at risk in clearance
Remember Winging plus no overhead reach: serratus anterior.
Exam trap Trapezius palsy also limits overhead abduction, but its winging is milder and the shrug is weak.
Why the other options are wrong
- Elevation of the scapula (shrugging) Upper trapezius and levator scapulae.
- Retraction of the scapula Rhomboids and middle trapezius.
- Lateral rotation of the humerus Infraspinatus and teres minor.
- Adduction and medial rotation of the arm Latissimus dorsi, pectoralis major and teres major.
A 19-year-old wrestler has had three anterior shoulder dislocations in a year, each with less force. Which of the following best explains the recurrence?
Answer: Detached anteroinferior labrum (Bankart)
In an anterior dislocation the humeral head is forced forwards and downwards, stripping the anteroinferior labrum together with the attached inferior glenohumeral ligament from the glenoid rim (Bankart lesion). This removes the labral bumper and the main anterior restraint in abduction and external rotation, so the shoulder redislocates with less and less force. Young, active patients have the highest recurrence rates. Cuff tears are more typical after dislocation in patients over about 40.
Bankart lesion
- Anteroinferior labrum and IGHL torn off the rim
- Loss of the main anterior restraint
- Young athletes: high recurrence
- Hill–Sachs: the matching head defect
Remember Recurrent anterior dislocation in the young: Bankart lesion.
Exam trap Over 40, persistent weakness after dislocation is more often a cuff tear than an axillary nerve palsy.
Why the other options are wrong
- Rupture of the long head of biceps Gives a distal bulge in the arm, not instability.
- Supraspinatus tendon tear More typical after dislocation in older patients.
- Axillary nerve palsy Causes deltoid weakness and numbness, not recurrence.
- Tear of the coracoclavicular ligament An acromioclavicular injury, not glenohumeral.
After axillary node clearance for breast cancer, a 48-year-old woman finds it hard to climb a ladder and to reach into her back pocket. The injured nerve ran with the subscapular vessels on the posterior wall of the axilla. Which nerve is it?
Answer: Thoracodorsal nerve
The thoracodorsal nerve (C6–C8, from the posterior cord) runs down the posterior wall of the axilla with the thoracodorsal branch of the subscapular artery to supply latissimus dorsi. Latissimus extends, adducts and medially rotates the arm, so climbing, swimming strokes and reaching the back pocket become weak. In axillary clearance it is identified and preserved, as is the long thoracic nerve on the medial wall. The intercostobrachial nerve crosses the axilla but is purely sensory.
Thoracodorsal nerve
- From the posterior cord (C6–C8)
- On the posterior axillary wall
- Supplies latissimus dorsi
- Weak extension, adduction, medial rotation
Remember Back-pocket and climbing weakness: thoracodorsal nerve.
Exam trap The thoracodorsal pedicle also supplies the latissimus dorsi flap used in breast reconstruction, so its injury matters later.
Why the other options are wrong
- Long thoracic nerve Lies on the medial wall; its injury causes winging.
- Intercostobrachial nerve Sensory to the inner arm; no weakness.
- Medial pectoral nerve Enters pectoralis minor and major from behind; no back-pocket weakness.
- Upper subscapular nerve Supplies the upper part of subscapularis, not latissimus.
Axillary lymph node levels are defined in relation to which muscle?
Answer: Pectoralis minor
For breast cancer surgery, axillary nodes are divided by pectoralis minor. Level I lies lateral (below) to it, level II behind it (including interpectoral Rotter nodes), and level III medial (above) to it, up to the apex of the axilla. Sentinel node biopsy usually finds the sentinel node in level I.
Axillary levels
- Level I: lateral to pectoralis minor
- Level II: behind it
- Level III: medial to it
Remember Pec minor is the ruler.
Exam trap Rotter nodes lie between pectoralis major and minor.
Why the other options are wrong
- Pectoralis major Forms the anterior wall but is not the reference.
- Latissimus dorsi Posterior wall.
- Serratus anterior Medial wall.
- Subscapularis Posterior wall.
A 50-year-old painter has shoulder pain only between about 60° and 120° of active abduction, easing above this. What is the mechanism?
Answer: Supraspinatus catching under the acromion
In the middle range of abduction the greater tuberosity and the supraspinatus tendon pass beneath the coracoacromial arch, so an inflamed tendon or subacromial bursa is squeezed (impingement). Below about 60° and above 120° the tendon is clear of the arch, so pain eases. Pain only at the top of elevation, above about 160°, points to the acromioclavicular joint. Arthritis and frozen shoulder restrict movement in all directions rather than producing a painful arc.
Painful arc
- 60–120°: subacromial impingement
- Supraspinatus under the coracoacromial arch
- Above 160°: AC joint
- Global stiffness: not impingement
Remember Mid-arc pain: supraspinatus under the acromion.
Exam trap A painful arc with good power suggests tendinopathy; marked weakness suggests a cuff tear.
Why the other options are wrong
- Glenohumeral arthritis with cartilage loss Painful and stiff through the whole range, often with crepitus.
- Acromioclavicular joint degeneration Gives a high painful arc, above about 160°.
- Contracted capsule of frozen shoulder Causes global loss of motion, especially external rotation.
- C5 root compression in the neck Gives neck pain and dermatomal signs, not an arc.
Where this sits in the CPSP syllabus
- Paper 1: Upper limb, Axilla, pectoral region and shoulder girdle; rotator cuff
- Surgery & Allied, Paper 2: Upper limb, Axilla, pectoral region and shoulder girdle; rotator cuff