L36. Joints of Upper Limb 1: Shoulder complex

Question 1

What are the main bones of the upper limb? [6]

Answer 1

Clavicle
Scapula
Humerous (head, neck, shaft and trochlea)
Radius
Ulna
Carpels, metacarpels and phalanges

Question 2

What is a synovial joint?

Answer 2

The most common and most movable type of joint

Lines articular surfaces covered by hyaline cartilage.

Question 3

What are the major features of a synovial joint?

Answer 3

1. Synovial cavity containing synovial fluid which enables movement (range and friction free) of the joint and nourishment to the cartilage
2. Fibrous capsule surrounding the synovial cavity connecting it to surrounding tissue
3. Synovial membrane lining the inner surface of the articular capsule is a thin (cells of this membrane secrete the synovial fluid)
4. Periostium: a dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints

Question 4

What is important to remember about hyaline cartilage?

Where would be the weak points in it?

Answer 4

Hyaline cartilage is avascular and aneural. This means there there is a very narrow space through it that carries neuro and vascular structures. It is this space that is the weakest area and most prone to damage.

Question 5

Where to the joints derive stability and strength from?

Answer 5

The fibrous capsule may be reinforced by stabliser muscles, intrinsic ligaments (intrinsic ligament is fused to or incorporated into the wall of the articular capsule) or extrinsic/accessory ligaments (ie. located distant from the joint)

Question 6

Does synovial membrane cover the articular/hyaline cartilage?

Answer 6

Never

Question 7

What are the special structures that make up some joints?[6]

Describe what each structure does

Answer 7

1. LABRUM: fibrocartilaginous rim that deepens the socket in ball & socket joint (for shallow articular surfaces) = increases congruence/matching of surfaces.
2. FAT PAD: intra-articular fat that fills up irregularities in the articular surfaces. They are always extra-synovial. Movement spreads synovial fluid - sponge action
3. INTRA-CAPSULAR TENDON: strength and stability
4. DISCS & MENISCI: associated with shock absorption, weight baring and shock absorption. They have a nerve and blood supply to its outer third.
5. LIGAMENTS: thickenings within the capsule eg. the cruciate ligaments to strengthen the joint.
6. BURSAE: a purse/sac of synovial fluid that communicates with the joint. Protects ligament, tendon and/or bone.

Question 8

What is important to note about the specialised intra-capsular ligaments?

Answer 8

They can be damaged and often in children. They are stronger than the boney attachments during growth and tearing of the ligament may involve evulsion of part of the bone away from it.

Question 9

What are the 2 broad types of joints in the upper limb? What are their features?

Answer 9

1. STABLE JOINTS:
   - Congruent (fit together well), often deep articular surfaces
   - They form tight capsules with strong ligaments
   - Have a very limited range of movement
2. MOBILE JOINTS:
   - Stability is dependent on additional sources: stabiliser and fixator muscles
   - Larger range of movement
   - They are susceptible to subluxation or dislocation (separation of joints)

Question 10

What are the main joints of the upper limb? [4]

Answer 10

Clavicular joints: sternoclavicular and acromioclavicular
Gleno-humeral joint
Scapulo-thoracic joint

Question 11

Describe the scapula

Answer 11

The shoulder blade
Triangular bone with a medial, lateral and superior border

The posterior aspect contains a spine that divides the scapula into the supraspinous process and the infraspinous process (both of which attach to muscle)

Question 12

Light passes through the scapula very easily (translucent, thin bone) what does this suggest?

Answer 12

There are no tendinous attachments on the fossa: mostly attachment via muscle fibres

Question 13

Describe the glenoid fossa.

What are the 2 processes off it?

Answer 13

It is a shallow cavity on the suprolateral border of the scapula. It is the site for the gleno-humeral joint (with the head of the humerous).

Coricoid process off the anterior suprolateral border and the acromial process off the posterior. - for muscle and tendinous attachments

(also contains tubercles for muscle attachment)

Question 14

Describe the clavicle, especially the shape of it. Why is it of this shape?

Answer 14

The clavicle is the only CURVED bone in the upper limb. The curvature is an evolutionary result of the route of important vascular and neural structures including the subclavian veins and arteries and the branches of branchial plexus, which pass under the clavical.

Question 15

What is the major function of the clavicle?

Answer 15

To push the shoulder joint away from the trunk, to the side (spokes wheel) to increase the range of motion of the upper limb without impedence on the thorax. (orientates the shoulder laterally)

Question 16

Describe ligamentous attachments onto the clavicle

[5]

Answer 16

On the inferior edge of the clavicle are two surfaces of ligamentous attachment:

1. Sternoclavicular ligament - attaches to the sternum medially
2. Costoclavicular ligament (medial to the sternoclavicular ligament) attaches to the superior margin of the first rib.
3. Interclavicular ligament attaches the most medial end of the clavicle to each other and to the top of the sternum
4. Laterally the clavical articulates with the acromion of the scapula by the acromioclavicular ligament
5. The coracoclavicular ligaments also attach the lateral clavicle to the coricoid process of the scapula

Question 17

What is the scapulo-humeral rhythm? What is the ratio of shoulder (joint) to scapular movement.

Answer 17

The COORDINATED MOVEMENT of the scapula across the thoracic cage together with the movement of the humerous to the glenoid

ie. the sliding of the scapula at the ‘scapulo-thoracic joint’ with a ratio of about 2:1 shoulder to scapular movement.

Question 18

What makes the clavicle a common site of fracture?

Answer 18

The site of curvature of the bone is a site of weakness.
- between the lateral third and medial 2/3 of the bone (between the 2 powerful ligaments). This means the structures are endangered.

Question 19

What are the major features of the sternoclavicular joint?

Answer 19

The sternoclavicular joint is very stable
An intra-articular disc and strong capsule

The joint is divided into 2 cavities to increase the complexity of movement on each side: both elevation and depression and in rotation

The costoclavicular ligament (accessory ligament that adds strength)

Question 20

Is the sternoclavicular joint readily disrupted? Why or why not?

Answer 20

The sterno-clavicular joint is rarely disrupted. However in cases of motor vehicle accidents (MVA) or direct force on the upper part of the chest, the joint can be disrupted.

Question 21

What is sterno-clavicular subluxation?

Answer 21

most likely associated with trauma
rare
very dangerous when it does occur

Question 22

Describe the major features of the acromioclavicular joint

Answer 22

is a plane synovial joint with its articular surfaces in the sagittal plane

it has a weak capsule (not a strong joint) - likely disrupted capsule occurring

Question 23

What is the main stabiliser of the acromioclavicular joint?

Answer 23

The coraco-clavicular ligament (accessory ligament)
which has 2 parts (separated by a bursa)
- trepezoid part and a conoid part (both prevent upward rotation of clavicle at the joint)

The acromioclavicular ligament is less stable but also helps

Question 24

Describe acromioclavicular subluxation

grading

Answer 24

Commonly due to a fall on the point of shoulder leading to separation of articular surfaces

• Grade 1: Acromioclavicular ligament stretching but not torn
• Grade 2: Acromioclavicular ligaments are torn and disrupted
• Grade 3: acromioclavicular and coracoclavicular ligaments are ruptured leading to wide separation of the joint (acromion is driven under the clavicle)

Question 25

Describe the layering of the glenohumeral joint

Answer 25

Concentric rings:

1. layer one (innermost) is bone
2. labrum (deepens socket)
3. Capsule (reinforced by intrinsic ligaments)
4. tendons (of the rotator cuff)
5. Coraco-acromial (Accessory ligament/arch and sub-acromial bursa)

Question 26

What are the typical features of a long bone?

Answer 26

Have a shaft, proximal and distal ends with epiphyses on both ends (the end part of a long bone, initially growing separately from the shaft)

Question 27

What are the fracture sites of the humerous? [3] What structures do these fractures endanger (ie. what structures pass beneath, beside them?)

Answer 27

1. Surgical neck (common in the elderly) - endangers the axillary nerve
2. Mid-shaft - endangers the radial nerve
3. Suprachondylar (ridges at distal end) - endangers median nerve and brachial artery

Question 28

Describe the articular surfaces of the glenohumeral joint

Answer 28

Synovial ball-and-socket joint
There is a missmatch (especially in abduction) as the head of the humerous is very large and the surface of the glenoid fossa is very shallow leading to relative INSTABILITY

Question 29

How is the glenoid socket made deeper?

Answer 29

The glenoid labrum

It has attachment superiorly for the long head of biceps and the glenohumeral ligaments

Question 30

The glenohumeral joint has a loss (folded inferiorly) capsule surrounding it - what is the significance of this?

What are its attachments?

Answer 30

This allows for a large range of movement inn three planes

Attaches to: anatomical neck above, surfical neck below

Question 31

There are deficiencies/holes in the capsule. What is their significance?

Answer 31

Permit the tendon of the long head biceps to pass down along the humerous (it also picks up some synovial membrane as it passes through the opening) = decreases friction.

This tendon acts like a gyrope that holds the head of the humerous

Question 32

What does the dependent (inferior fold) of the capsule allow for?

Answer 32

Abduction and movement in ALL planes

Question 33

Describe the bursa of the glenohumeral joint

Answer 33

Lies deep to the subclapularis muscle (communicates with the joint) - a very small bursa

Question 34

What is adhesive capsulitis?

Answer 34

Happens in elderly or after injury: the capsule contracts causing a ‘frozen’ shoulder constricting the range of movement of the joint

Question 35

What is the rotator cuff of the shoulder?

What is the main role?

Answer 35

Muscles (four) located deep to the deltoid muscle that originate from the scapula and insert into the capsule. - merge at the capsule.

Contraction of the muscles is around the joint and hence the major function of them is to stabilise the joint - pulls the head of the humerous towards the glenoid fossa (but also act as prime movers)

Question 36

What are the muscles that make up the rotator cuff?

Answer 36

1. Supraspinatus
2. Infraspinatus
3. Subscapularis
4. Teres minor

Question 37

What happens if the rotator cuff is weakened?

Answer 37

The humerus is susceptible to slide upwards with the antagonist pull of the deltoid (this tears the labrum or compresses the supraspinatus tendon) leading to vascular reactions or calcium deposits in the capsule

Question 38

What is the coracoacromial ligament?

Answer 38

The least significant stabilising ligament of the glenohumeral joint between the coracoid process and acromium of the scapula.

It doesn’t resist movement

Question 39

What is the function of the coracoacromial ligament?

Answer 39

It is just above the shoulder joint and provides superior protection

Question 40

Where is the coracoacromial bursa?

Answer 40

Located deep to the acromion process (between the 2 points)

Question 41

What is one of the largest pathologies of the shoulder joint?

Answer 41

A supraspinous injury where the humerus slides upwards and deltoid pulls it up and the supraspinatus tendon is torn leading to vascular reactions and calcium deposition.

Question 42

What kind of pathologies can occur in the rotator cuff?

How can they be measured?

Answer 42

The shoulder can be disrupted that the head of the humerus tears through the superior capsule of the shoulder (glenohumeral joint) and causing a pseudojoint under the surface of the chromium process.

The painful arc of movement in these joints tends to be between the 60 and 120 degrees.

Question 43

The shoulder is a ball and socket joint that is prone to pathology. What are the 2 major pathology types?

What type of movement is this most common with and why?

Answer 43

Subluxation (partial separation)
Dislocation (complete separation)

Most common in abduction as there is least contact between the two joining bones in this action

Question 44

What is the most common shoulder dislocation?

Answer 44

Anterior and inferior where the forces applied to an abducted and externally rotated arm.
(posterior is associated with electric shock or grand mal seizures)

Question 45

What are the potential consequences of shoulder dislocation?

Answer 45

The posterior cord of the brachial plexus (gives rise to axillary nerves) runs through in the quadrangular space along the shaft of the humerus.

Dislocation can impinge the nerve impairing supply to the deltoid and overlying skin (deltoid loses tension and thus loss of curvature of the shoulder is seen)

Must never ask patient suspected of this to abduct arm, rather do sensory cutaneous skin pricks to determine impinged axillary nerves.