Session 16 - The Shoulder, Muscles of the Scapula and Posterior Arm

Question 1

Which muscles are responsible for shoulder abduction?
Initiates by?
What takes over?
Rotation of scapula requires?

Answer 1

 Initiated by supraspinatus (first 200 or so)
 Deltoid then takes over
 Rotation of the scapula is required to raise the arm above the head – this
requires the action of trapezius.

Question 2

Describe the movements of the scapula and the humerus during shoulder
abduction
Initiated by?
What takes over?

Answer 2

 Abduction of the arm at the shoulder is initiated by supraspinatus (first
20 deg or so)

 Deltoid then takes over

 As the arm rises, the humerus laterally rotates – this keeps the articular
surfaces in contact with each other; in full abduction (with the arm above
the head) the humerus has rotated 90 deg

 For every 2 deg of abduction at the shoulder joint the scapula rotates 1 deg

Rotation tilts the glenoid fossa cranially.

Question 3

Which nerve innervates trapezius?
How would you test if the nerve was
functioning?

Answer 3

Accessory nerve

Shrug shoulders - elevate the scapula

Question 4

Which nerve is at risk of injury in shoulder dislocation?
What functional deficits would result and how would you examine a patient to test for these deficits?
(Motor and Sensory)

Answer 4

The axillary nerve (C5-C6 fibres)
Weakness of deltoid and teres minor
Impaired sensation to skin of the upper lateral shoulder

Motor function - abduct arm
Sensory function - light touch on upper lateral shoulder

Question 5

What structures stabilise the shoulder joint?

Answer 5

Rotator cuff is key stabilise

Tendon of long head of biceps

Question 6

Which parts of the pectoral girdle and shoulder joint can be palpated on
examination? (4 things)

Answer 6

Clavicle
Acromion
Spine of scapula
Lateral border of scapula

Question 7

The triceps and posterior compartment of the forearm are innervated by?

Answer 7

Radial nerve

Question 8

Triceps function

Answer 8

Extend elbow

Question 9

Posterior compartment of forearm function

Answer 9

Extends the wrist

Question 10

Scenario : Mid shaft fracture
What movements could you test to try and ascertain whether the radial nerve
had been injured?

Term given to an injury for this area?

Answer 10

Ask patient to extend elbow and extend wrist

Wrist drop

Question 11

How many heads does triceps have?

Answer 11

3

Question 12

By the time the radial nerve has reached the mid-humeral level what has it already given off? and to which muscle area?

Answer 12

Multiple branches to the proximal parts of the muscle

Question 13

Why might triceps be weak compared to the unaffected arm, but not paralysed?

Answer 13

As the triceps has 3 heads they arise from many different regions proximally

If you get a nerve injury in the mid-humeral level the downstream muscles will be impacted

But multiple branches have already been given off by this time to proximal parts of the muscles

Therefore these will be unaffected and still function

So triceps are weak but not paralysed

ESSENTIALLY:
Radial nerve gives off multiple branches which innervate multiple muscles proximally - these can’t all be damaged so a proportion of triceps function will be retained

Question 14

Which muscles comprise the rotator cuff, and where do they insert on the
humerus?

Answer 14

Supraspinatus - Superior facet and greater tubercle

Infraspinatus - Middle facet and greater tubercle

Teres Minor - Inferior facet and greater tubercle

Subscapularis - Lesser tubercle

Question 15

Which 2 muscles does the axillary nerve innervate?

Answer 15

Deltoid

Teres Minor

Question 16

Trapezius is innervated by?

Answer 16

Accessory nerve