by Hannah Farrell
Our expert witnesses in shoulder surgery can opine on all shoulder related problems and provide medico-legal reports giving an opinion on breach of duty, causation, current condition, and prognosis. Read on for an overview of shoulder anatomy, what can go wrong, and what surgical intervention is available.
Anatomy of the Shoulder
The shoulder joint (glenohumeral joint) is the major joint connecting the upper limb to the torso. The shoulder joint is an incredibly mobile ball and socket joint, which is relatively unstable and susceptible to injury.
The head of humerus forms the “ball”, whilst the glenoid fossa of the scapula forms the “socket”. These two surfaces are covered with hyaline cartilage to allow smooth articulation. As the head of humerus is much larger than the glenoid fossa, it has a wide range of movement. The glenoid fossa also has a rim of fibrocartilage, known the glenoid labrum, which acts to deepen the fossa.
The shoulder joint is enclosed by the joint capsule; a fibrous, but somewhat lax, sheath extending from the neck of the humerus to the border of the glenoid fossa. The inner surface of the joint capsule is lined by a synovial membrane which serves in reducing friction within the joint; this is achieved through synovial bursae, which are sacs of synovial fluid which cushion structures within the joint.
The shoulder typically has two main bursae:
- Subacromial bursae – deep within the joint, promoting free movement of the rotator cuff tendons; and
- Subscapular bursae – between the tendon and scapula, reducing wear and tear of the subscapularis tendon.
As the shoulder joint needs to be very mobile, it is naturally quite unstable. However, in order to increase stability, it has a complex system of ligaments supporting the bony structures. The ligaments of the shoulder include:
- Glenohumeral ligaments – main source of joint stability, preventing the joint from dislocating anteriorly;
- Coracohumeral ligament – supports the superior aspect of the joint capsule;
- Transverse humeral ligament – secures the tendons of the long head of the biceps muscle (biceps tendon) into the intertubercular groove;
- Coraco-Clavicular ligament – formed by the trapezoid and conoid ligaments, working with the acromioclavicular ligament to keep the clavicle aligned in relation to the scapula; and
- Coracoacromial ligament – prevents superior displacement of the head of humerus.
Surrounding the shoulder joint are a group of muscles known as the rotator cuff muscles. These are attached, by their tendons, to the humerus and fused to the joint capsule. The resting tone of these muscles forces the head of humerus into the glenoid fossa. The rotator cuff muscles include:
- Subscapularis
- Supraspinatus
- Infraspinatus
- Teres minor
The shoulder joint also has a complex neurovascular system, including:
- Arterial supply:
- Branches of axillary artery, including anterior and posterior circumflex humeral arteries;
- Branches of suprascapular artery;
- Thyrocervical trunk artery;
- Veinous drainage:
- Cephalic vein;
- Basilic vein;
- Nervous supply:
- Axillary nerve;
- Suprascapular nerve;
- Lateral pectoral nerve;
What can go wrong with the shoulder joint?
Due to its huge range of motion and flexibility, the shoulder joint is relatively unstable and therefore susceptible to trauma. As described above, there are also numerous structures within the shoulder joint which can become damaged either through trauma or general wear and tear.
Adhesive Capsulitis (Frozen Shoulder)
This condition is caused when the shoulder joint capsule contracts and adheres to the head of humerus. Consequently, the shoulder is painful and has a reduced range of movement. Often, there is no known cause (primary adhesive capsulitis), however it may be associated with other conditions (secondary adhesive capsulitis), including rotator cuff tendinopathy, subacromial impingement syndrome, biceps tendinopathy, previous surgery, or trauma.
If indivdiuals find that conservative therapy and physiotherapy have no effect on the condition, shoulder surgery may be offered. In such instances, the shoulder joint can be manipulated to remove the adhesions from the humerus. Other surgical interventions include surgical release of the joint capsule or arthrographic distention (a procedure using an injection of fluid to break areas of adhesions).
Rotator Cuff Tear
Rotator cuff tear is an injury to any one of the four muscles (and their tendons) comprising the ‘rotator cuff’ (as described above), which provide movement and stability of the shoulder. A rotator cuff tear may be classified as acute or chronic, and partial thickness or full thickness. A full thickness tear can then be further categorised as small, medium, large, or massive.
An acute rotator cuff tear may occur following a minimal traumatic force (if there is already degeneration present) or larger traumatic forces (even if there is no degeneration present). Chronic rotator cuff tears occur over a period of time where there have been multiple degenerative microtears.
A Clinician may perform specific tests to help diagnose a rotator cuff tear. These include:
- Jobe’s test (detects supraspinatus injury);
- Gerber’s lift-off test (detects subscapularis injury); and
- Posterior cuff test (detects injury to infraspinatus and teres minor).
Surgical intervention may be indicated and can be performed arthroscopically or via open surgery.
Subacromial Impingement
The rotator cuff tendons pass through the subacromial space in the shoulder, along with the long head of the biceps tendon, and the coraco-acromial ligament. Inflammation and irritation in this area can lead to pain, weakness, and a reduced range of movement.
Clinicians can perform two specific tests:
- Neers impingement test; and
- Hawkins test.
Whilst conservative treatment is the preferred method of treatment, some individuals with persistent problems may require shoulder surgery. Usually performed via arthroscopy, surgery can involve repair of tears to any muscles, removal of subacromial bursa, or removal of part of the acromion (increasing the volume of the subacromial space).
Shoulder Dislocation
One of the most common traumatic injuries to the shoulder is dislocation of the shoulder joint. Dislocations of the shoulder joint include:
- Anterior dislocation i.e., the head of humerus is moved forwards out of the glenoid fossa;
- Posterior dislocation i.e., the head of humerus is moved backwards away from the glenoid fossa; and
- Inferior dislocation i.e., the head of humerus is moved down out away from the glenoid fossa.
An anterior dislocation of the shoulder is occurs most commonly as the head of humerus is forced through the weakest part of the joint capsule. There are multiple complications associated with an anterior shoulder dislocation:
- Torn joint capsule – this increases the susceptibility to further dislocations;
- Hill-Sachs lesions – the head of humerus fractures from the impact against the glenoid;
- Bankart lesions – part of the labrum becomes detached, sometimes with a piece of bone becoming avulsed (avulsion fracture)
Other complications of shoulder dislocation include:
- Nerve damage, particularly to the axillary nerve which runs close to the shoulder joint and around the neck of humerus;
- Vascular damage; and
- Torn muscles, tendons, or ligaments.
If a fracture has been identified, then the shoulder will require surgery to reduce it. However, should there be no fracture, then there are several methods of performing a closed reduction:
- Hippocratic;
- External rotation;
- Stimson’s technique;
- Kocher’s method;
- Immediate reduction i.e., if a doctor witnesses a dislocation and is confident there is no fracture.
Following any reduction, a full neurovascular assessment should be performed and adequate analgesia and physiotherapy prescribed.
Fractured Shoulder
A fractured shoulder usually encompasses a fracture of the proximal humerus, often resulting from a fall onto an outstretched hand. As the circumflex blood vessels and axillary nerve wrap around the neck of humerus, they are particularly at risk of succumbing to damage in such injuries.
The Neer classification system is used to classify proximal humeral fractures into four different sections:
- Greater tuberosity
- Lesser tuberosity
- Anatomical neck (articular segment)
- Surgical neck (humeral shaft)
Different surgical techniques can be offered in different circumstances, including:
- Surgical fixation;
- Open reduction internal fixation;
- Intermedullary nailing;
- Hemiarthroplasty (replacement of head of humerus); and
- Reverse shoulder arthroplasty.
Shoulder Osteoarthritis
Osteoarthritis (wear and tear) in the shoulder joint is common due. Whilst conservative treatment with medication is the first line of treatment, surgical intervention may be required. Options of shoulder surgeries include;
- Shoulder arthroscopy – keyhole surgery of the joint;
- Shoulder arthroplasty:
- Hemiarthroplasty – replacement of the head of humerus;
- Total shoulder arthroplasty – replacement of both the head of humerus and glenoid;
- Reverse total shoulder arthroplasty – an option for individuals who have rotator cuff tear arthropathy, whereby the head of humerus and glenoid are both replaced, however they are inserted in opposite locations i.e., the ball is attached to the glenoid, and the cup is attached to the humerus; and
- Resection arthroplasty – used to treat acromioclavicular joint arthritis.