Orthopaedics - Shoulder Flashcards
What causes shoulder instability?
Shoulder instability can be caused by an acute dislocation (of which anterior dislocations are most common). But instability can also be a problem without frank dislocation.
Causes of Instability can be considered under:
1) problems caused by an acute dislocation (e.g. rotator cuff tear)
2) structural defects that predipose to repeated dislocation
3) dislocation in the absence of a structural defect
What are the 4 rotator cuff muscles?
These are a group of muscles that form a hood around the proximal humerus and stabilise the glenohumeral joint. They are:
- supraspinatus - abducts in the plane of the scapula
- subscapularis - internally rotates the humerus
- infraspinatus - externally rotates the humerus
- teres minor - externally rotates the humerus when in abduction
What is the difference between a chronic and an acute rotator cuff tear?
A chronic rotator cuff tear may occur in the elderly without any history of trauma due to tendon degeneration. Chronic rotator cuff tears are problems of there own, and if partial are usually managed conservatively.
Acute cuff tears are the result of injury to a previously normal rotator cuff. They are common after dislocation in middle aged patients when they complain of weakness and pain.
How should an acute rotator cuff injury be managed?
X- rays should be performed to rule out a fracture followed by either an MRI or ultrasound to delineate the tendons of the rotator cuff.
Management is usually surgical for an acute cuff tear. Results of repair are better if performed within 3 months of the injury. This can be by open surgery or arthroscopically. Arthroscopic procedures have a quicker return to work rate but function is equal after 6 months for both approaches.
Is it possible to distinguish between a partial and a complete rotator cuff tear?
Yes. As well as being acute or chronic, rotator cuff tears can also be classified based on whether they are partial or complete.
In a partial tear, the intact tendon fibres allow vascular ingrowth and repair to occur. In a complete tear there is little or no reaction and no repair. Pain is abolished by injecting a local anaesthetic. If active abduction is now possible the tear must only be partial.
What are the 2 types of lesion that can cause recurrent dislocations?
When a shoulder is dislocated the glenoid or the head of the humerus can become damaged. This makes the shoulder joint unstable and it frequently dislocates even with minimal force.
2 lesions in particular are associated with a previous dislocation that causes shoulder joint instability and predisposes to further dislocations. These are the Bankart lesion and the Hills-Sachs lesion.
What is a Bankart lesion? How is it investigated?
A dislocation can tear off the cartilagenous labrum (lip of the glenoid fossa). This is known as a Bankart lesion.
If this is associated with a chip off the rim of the glenoid it is called a bony Bankart lesion. Both can be associated with recurrent dislocations.
Investigations include a CT to evaluate bone loss and an MRI arthrogram, where contrast is injected into the shoulder joint before an MRI is performed. Contrast can be seen leaking out of the shoulder through a tear in the labrum.
How is a Bankart lesion repaired?
Both Bankart and bony-Bankart lesions require repair due to the increased risk of future dislocation. They can both be repaired arthroscopically but if there is a very large bony-Bankart then an open approach is more appropriate. There are a number of operations to address a large bone loss of the glenoid, one is a Bristow-Latarjet procedure. Here the tip of the coracoid process and the conjoint tendon is removed and screwed into the front of the glenoid. This extra bit of bone builds up the front of the glenoid and prevents future anterior dislocations.
What is a Hill-Sachs lesion?
Sometimes the head of the humerus can be damaged in a dislocation. Because the humeral head is relatively soft, an anterior dislocation can lead to the bony glenoid forming a divot in the head. This is called a Hill-Sachs lesion.
As the shoulder is brought into external rotation, the glenoid “falls into” the bony defect in the head of the humerus. When this happens it is called an “engaging Hill-Sachs lesion”.
Treatment is surgical. Both the joint capsule and ligaments are pinned into the defect using a bone anchor. The result is to fill the defect and limit external rotation.
Why does hypermobility cause shoulder instability?
Hypermobility is a common cause of shoulder problems in younger patients. It causes dislocations in the absence of any structural defect.
The most common form is generalised hypermobility syndrome. It is most common in adolescent girls and may be due to the effects of hormones on soft tissue. The prognosis is good though. Patients tend to grow out of this and it is rarely a problem in adulthood. The main treatment modality is physiotherapy.
How is hypermobility diagnosed?
Hypermobility is diagnosed using the Beighton scoring system. This gives points for:
- hands flat on the floor (1 point)
- elbow hyperextension (2 points)
- knee hyperextension (2 points)
- thumb touches the forearm (2 points)
- little finger MCP hyperextension past 90 degrees (2 points)
Score is out of 9. >4 is abnormal.
What causes an anterior dislocation?
Dislocation causes shoulder instability.
Anterior dislocation of the shoulder is the most common. It usually follows an acute injury in which the arm is forced into abduction, external rotation and extension - i.e. throwing an object
The typical patient is a young man who complains of the shoulder repeatedly “going out of joint” during over-arm movements, and each time having to have it manipulated back into position.
What causes a posterior dislocation?
Posterior dislocation is rare; when it occurs it is usually due to a violent jerk in an unusual position - i.e. following an epileptic fit or a severe electric shock (lightning strike). Recurrent posterior instability is nearly always a subluxation, with the humeral head riding back on the posterior lip of the glenoid.
How does subluxation typically present?
It is important to remember that subluxation is a partial dislocation. Its presentation is less obvious. The patient may describe a “catching” sensation (rather than complete dislocation) followed by “numbness” or weakness.
What type of joint is the shoulder joint? What type of cartilage is present?
The shoulder joint is a ball and socket joint that permits movement in multiple planes (i.e. abduction, adduction, extension, flexion, internal and external rotation).
It is formed by the proximal head of the humerus articulating with the shallow glenoid fossa of the scapula. The glenoid is deepened by a fibrocartilagenous ring called the glenoid labrum.
Both articular surfaces are lined with hyaline cartilage.
