Shoulder

The shoulder is a complex area in the body and contains an incredibly mobile ball & socket joint, which comes at the expense of the joint stability. Basically, many things can go wrong and it is important to understand how the joint works properly to diagnose and help patients well! Let’s start by revising bony anatomy of the bones involved.

Bones

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Fig 1. Bony prominences of clavicle
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Fig 2. Anatomy of humerus
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Fig 3. Lateral, posterior and costal views of scapula

Shoulder joint type

  • Ball and socket type
  • Head of humerus articulates with the glenoid cavity of the scapula (hence known as glenohumeral joint)
  • Multiple bursae (synovial fluid filled sacs that tend to reduce friction) – e.g. subacromial, subscapular, subaracoid
  • Stability hugely down to rotator cuff muscles, ligaments, biceps tendon & glenoid labrum (a fibrocartilagenous ridge that surrounds the glenoid cavity to compensate for the large humeral head)

Ligaments of shoulder joint

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Fig 4. Ligaments of shoulder joint
  • Glenohumeral ligaments also known as capsular ligaments
    • superior, middle & inferior ligaments
    • from scapula (supraglenoid tubercle) to lesser tubercle of humerus
    • stabilise the joint anteriorly
  • Coracohumeral ligament
    • from scapula (coracoid process) to greater tubercle of humerus
    • supports the joint superiorly
  • Transverse humeral ligament
    • from greater to lesser tubercle of humerus
    • holds the tendon of the long head of biceps in the intertubercular groove
  • Coraco-clavicular ligament
    • conoid & trapezoid ligaments
    • from clavicle to scapula (coracoid process)
    • maintain the alignment between clavicle and scapula
  • Coracoacromial ligament
    • from acromion to coracoid process of scapula
    • forms the coracoacromial arch, which supports the joint superiorly & prevents displacement of humeral head

Rotator cuff

  • Group of muscles that originate from scapula and attach to humeral head
  • Offer stability to the joint by pulling the humeral head into the glenoid fossa
Screenshot 2018-12-16 at 14.30.07.png
Fig 5. Rotator cuff muscles

Supraspinatus

  • Origin – supraspinous fossa of scapula
  • Insertion – superior facet of greater trochanter of humerus
  • Innervation – suprascapular nerve (C5-C6)
  • Action – ABDuction of arm 0-15 degrees & aids deltoid for 15-90 degrees

Infraspinatus

  • Origin – infraspinous fossa of scapula
  • Insertion – middle facet of greater trochanter of humerus
  • Innervation – suprascapular nerve (C5-C6)
  • Action – lateral rotation of arm

Teres minor

  • Origin – posterio-lateral surface of scapula
  • Insertion – inferior facet of greater tubercle of humerus
  • Innervation – axillary nerve (C5-C6)
  • Action – lateral rotation of arm

Subscapularis

  • Origin – subscapular fossa of costal scapula
  • Insertion – lesser tubercle of humerus
  • Innervation – upper & lower subscapular nerves (C5-C6)
  • Action – medial rotation of arm
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Fig 6. Shoulder joint movements by muscle

A helpful resource to revise clinical assessment of a shoulder joint & to understand the clinical correlation of signs to the anatomy reviewed is available below – Geeky Medics!

To summarise, important special tests are:

  • Empty can test – assesses supraspinatus
    • straighten out arm and turn hand thumb facing down as if emptying a can & check resistance if arm pressed down
  • Painful arc test – assesses supraspinatus/impingement
    • passive ABDuction of patient’s arm – any pain, commonly between 60-120 degrees
  • External rotation against resistance – assesses infraspinatus/tendonitis
    • elbow flexed at 90 degrees, tucked in side & externally rotate against resistance
  • External rotation in abduction – assesses teres minor
    • arm at 90 degree abduction with elbow at 90 degree, passively externally rotate the shoulder – if unable to keep the arm in this position test positive
  • Internal rotation against resistance – assesses subscapularis/tear
    • dorsum of hand on lower back and patient to press away from back & apply resistance

References

 

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