MSK 4.2 Shoulder Joint Flashcards
(22 cards)
1) What type of joint is the shoulder joint?
2) What is the attchment point for rotator cuff muscles?
Review of the osteology: scapula & humerus
What is the name of the shoulder joint?
Why is this joint unstable?
How is stability achieved?
1) Glenohumeral joint. Ball and socket joint. Head of humerus sits in glenoid cavity of scapula
2) Glenoid cavity is very shallow. Stability relies heavily on
- Glenoid labrum (fibrocartilage ring, deepends the socket)
- Rotator cuff muscles (dynamic stabalisers)
- Ligaments
- Big head of humerus → disproportionate articular surfaces
- Very mobile (multiplanar movements)
- Hyaline cartilage - covers articular cartilages for smooth movement.
3) Rotator cuff muscles (main stabalisers)
Important ligaments in the shoulder joint
1) What is the shoulder capsule?
2) Where does it attach?
3) Why is it “lax”?
4) “Small opening anteriorly”
1) A bag of tough connective tissue that surrounds the entire shoulder joint.
Purpose: holds everything together but still allows full movement.
2) Top: around the glenoid labrum & edge of glenoid cavity (socket).
Bottom: around the anatomical neck of the humerus.
Also bridges the intertubercular groove to hold the long head of biceps tendon in place.
3) The capsule is loose enough (especially inferiorly) to allow:
Full abduction Full rotation
This laxity = great mobility
But this is also why the shoulder is prone to dislocation.
4) There’s a tiny hole that allows the subscapular bursa to communicate with the joint
1) What is the synovial membrane?
2) Where does it line?
3) Long head of biceps tendon involvement:
4) Subscapular bursa communication:
1) It’s the inner lining of the joint capsule.
It produces synovial fluid → lubricates the joint for smooth movement.
2) ines the inside of the capsule (up to where cartilage starts).
Covers everything except the actual articular surfaces (which are covered by hyaline cartilage).
3) he tendon of the long head of biceps actually passes inside the joint cavity.
The synovial membrane wraps around this tendon like a little sleeve to protect it while it moves.
The tendon inserts into the supraglenoid tubercle on the scapula.
4) There’s a little gap in the anterior capsule that allows the joint cavity to communicate with the subscapular bursa.
This is why inflammation (like in arthritis) can sometimes spread between the two.
The synovial membrane lines the inside of the capsule, surrounds the long head of biceps tendon inside the joint cavity, and produces synovial fluid.”
1) What are the two types of ligaments present in the glenohumeral joint?
1) Extracapsular Ligaments (outside the joint capsule)
2) Intracapsular Ligaments (inside joint capsule)
Extracapsular ligaments anatomy
Intrascapular ligaments anatomy
1) What is the coracoacromial arch?
2) Why does it exist?
3) Why does this matter clinically?
1) It’s the roof of the shoulder joint.
Formed by:
Coracoacromial ligament
Acromion
Coracoid process
✅ 🔑 SUPER SIMPLE:
It’s a bony + ligament roof sitting over the head of the humerus.
2) Prevents superior (upward) dislocation of the humeral head.
Acts like a hard ceiling above the joint.
3) The space between this arch and humeral head = subacromial space.
Structures inside this space:
Supraspinatus tendon Subacromial bursa Long head of biceps tendon
If the space narrows → impingement →
→ leads to painful arc syndrome (50–130° abduction pain)
“Coracoacromial arch = roof over shoulder joint → involved in supraspinatus impingement & painful arc syndrome.”
Rotator Cuff Muscles SITS
1) Action
2) Nerve supply
3) Main overall functions
4) How do they strengthen glenohumeral joint
5) Supraspinatus tendon is seperated by CAA by
PURE EXAM LINE YOU NEED:
"Rotator cuff = SITS muscles stabilizing glenohumeral joint; supraspinatus starts abduction (0–15°), commonest torn in rotator cuff injury."
5) Subacromial bursa
Other muscles which stabalise glenohumeral joint
“Serratus anterior → protraction & upward rotation of scapula → long thoracic nerve (C5-C7). Injury → winged scapula.”
Role of serratus anterior
Innervation
Anatomy
Which ribs does it attach to?
Where is the subacrmial bursa?
What is its clinical significance?
“Subacromial bursa reduces friction between supraspinatus tendon (below) and deltoid muscle (above) during arm abduction.”
“Painful arc syndrome occurs due to supraspinatus impingement and/or subacromial bursitis.”
Where is the Subscapular Bursa?
What does it do?
Summary of shoulder movements
Summary: Stability of shoulder joint
🔥 🔑 The KEY EXAM FACT from this slide:
👉 Where is the shoulder least supported?
✅ 🔥 PURE ANSWER:
"Inferiorly."
Because:
There’s no strong muscle or ligament supporting inferiorly. That’s why most shoulder dislocations happen anterior-inferiorly
Shoulder Dislocation
- Mechanism
- Most common type
- On examination
🔥 Most common dislocation type:
Anterior + Inferior dislocation (below the coracoid process)
✅ 🔑 Mechanism:
Trauma while arm is:
Abducted
Externally rotated
Joint capsule + rotator cuff may tear → poor healing → recurrent dislocations.
✅ 🔑 Why anterior-inferior?
Inferior capsule is weak (least supported — you already know this). Once inferiorly displaced, strong pec muscles pull head of humerus anteriorly.
✅ 🔑 On examination:
Sign Description
Loss of normal round contour Shoulder appears squared off
Head of humerus location Lies below coracoid process
Patient posture Supports arm with opposite hand (very painful)
✅ 🔑 Posterior dislocation is rare
(usually due to seizures or electric shock).
🔥 PURE EXAM ONE-LINER:
"Most shoulder dislocations are anterior-inferior (below coracoid), occur after trauma on abducted/externally rotated arm; squared shoulder appearance."
1) Dislocation is typically inferior and anterior however defined anterior. Why?
2) How can a shoulder dislocation lead to recurrent dislocations
1) Clinically defined as anterior dislocation due to
humeral head locating anteriorly (pull of powerful
adductors)
2) “Anterior-inferior dislocation can tear capsule & rotator cuff (these structures provide stability)→ poor healing → recurrent dislocations due to loss of stability.”
Axillary nerve damage
1) How? WHY
2) What does this lead to?
1) Anterior shoulder dislocation (esp. inferior-anterior dislocation)
Fracture of surgical neck of humerus
he axillary nerve wraps around surgical neck of humerus.
Vulnerable when humeral head shifts forward or fractures.
Painful Arc Syndrome
1) What is the problem?
2) Risk factors
3) Symptoms
1️⃣ What is the problem?
Supraspinatus tendon rubbing (impinging) under the Coracoacromial Arch (CAA) during abduction.
Leads to:
Subacromial Bursitis (inflammation of subacromial bursa, +/- calcification)
Supraspinatus Tendonitis (+/- calcification)
Degeneration or rupture of rotator cuff tendons (if chronic)
🔥 2️⃣ Risk Factors:
Cause Explanation
Repetitive overuse Sports: racquet, climbing, swimming; overhead work
Ageing Degeneration of tendon with age
Avascularity of supraspinatus tendon Poor blood supply predisposes to damage
Anatomical variation Small anatomical differences can narrow subacromial space, increasing impingement risk
3️⃣ Symptoms:
Pain during shoulder abduction between 60° and 120° (Painful Arc).
Outside this range (before 60° and after 120°) — little or no pain.
Caused by:
Supraspinatus tendon impingement under the acromion
Inflammation of subacromial bursa
🔑 PURE EXAM GOLD ONE-LINER:
"Painful Arc Syndrome: supraspinatus tendon impinges under coracoacromial arch during 60°-120° abduction → supraspinatus tendonitis + subacromial bursitis."
AC Joint Dislocation - Shoulder Seperation
1) What is it?
2) Mechanism of injury
3) Structures involved
4) X-Ray Features
5) Repair
1) Injury to the Acromioclavicular (AC) joint — where clavicle meets acromion.
Can rupture coracoclavicular ligaments (conoid + trapezoid ligaments).
2) Fall onto tip of shoulder
Direct blow to shoulder
3)
4) Separation between clavicle and acromion → clavicle looks elevated.
Coracoclavicular distance increased if ligaments torn.
✅ 🔑 Key exam fact:
"AC joint dislocation = shoulder separation; rupture of coracoclavicular ligaments leads to clavicle elevation."
