Anatomy

The rotator cuff is a group of muscles consisting of subscapularis, supraspinatus, infraspinatus and teres minor arising from the scapula and inserting to the tuberosities around the humerus. They help in positioning of the arm by fine control of the glenohumeral joint.

The long head of biceps is intra-articular and arises from the supraglenoid tubercle of the glenoid fossa. It passes between the subscapularis and supraspinatus in the bicipital groove.

Extrinsic and intrinsic theories have been described. Intrinsic theory suggests tears developing within tendons due to changing properties within the tendon. Extrinsic theory states that the tears occur due to impingement of the cuff tendons in the subacromial space between the acromion and coracoacromial ligament for bursal sided tears. The articular sided tears are thought to be secondary to the impingement between the glenoid and the humerus on abduction and external rotation.

The anterior footprint of the supraspinatus is one of the commonest areas to suffer a tear in the rotator cuff due to its poor vascularity. Rotator cuff tears can be degenerative or traumatic. Degenerative tears are considered as defects in the rotator cuff. These tend to be gradual in onset and most patients are able to compensate for the tear with the other cuff muscles and the deltoid. They can be present in up to 54% of people over 60 yrs even though they are asymptomatic. The symptomatic cuff defects respond well to physiotherapy and symptomatic management with painkillers and steroid injections.

Traumatic tears tend to be bigger and result in a pattern of pseudoparalysis or weakness in the rotator cuff. These can be easily missed in the presence of a normal x-ray following a fall. Persistent pain and weakness in the shoulder following a simple fall or trauma should alert the possibility of a rotator cuff tear or a brachial plexus lesion. A lower threshold for surgical intervention is recommended in traumatic tears if the weakness is profound in an emergent fashion.

Presentation
Majority of the tears in the rotator cuff tend to be degenerative. It has an insidious onset of pain in the shoulder. The pain can be worse on certain movements (like the painful arc). It can affect their night sleep and ability to lie on the affected side. They also notice that the movements are restricted due to pain and are associated with weakness.

Clinical examination
Inspection of the shoulder can reveal wasting of supraspinous and or infraspinous fossa depending on the muscle involved and the time since the onset of the tear. Patients can be tender over the anterosuperior aspect of the shoulder if the anterior footprint of the supraspinatus is torn. Movements can reveal a painful arc with positive signs for subacromial impingement. Assessment of individual components of the rotator cuff would lead to the likely cuff that is torn. Usually passive movements are well preserved but active movements can be restricted due to pain.

Differential diagnosis

A full neurological assessment of a a pseudoparalytic arm following trauma needs to be performed to in order to rule out brachial plexus lesion
Isolated suprascapular nerve entrapment can occur secondary to a cyst or swelling in the suprascapular notch leading to weakness of the supraspinatus and infraspinatus.

Plain radiographs of the shoulder are usually normal. There can be associated changes of sclerosis on the greater tuberosity and under surface of the acromion in chronic situations. Ultrasound can be a useful diagnostic tool in the diagnosis of cuff pathologies. But it is operator dependant and it may be difficult to assess intra-substance tears/ partial tears of the rotator cuff. It can also be challenging to comment on the fatty atrophy on the ultrasound. MRI shoulder can give us more information about the degree of muscle wasting, fatty atrophy, size, location, degree of retraction, chronicity of the tear and potential repairability of the tear. The volume of muscle occupying the fossa can give us information about the muscle wasting on the parasagittal view of the shoulder.

Plain radiograph
Anterior greater tuberosity cysts that may be seen in rotator cuff tears
Superior migration of the humeral head
Glenohumeral degenerative changes
Ultrasound 
Extent of tear
Retraction
MRI scan
Extent of tear
Retraction
Muscle atrophy
Fatty infiltration

Classification according to:
Tendon torn
Site of tear
Length of tear
Tear thickness
Tear size

The mainstay of treatment in degenerative tears is conservative. Advice, painkillers and physiotherapy to strengthen the remaining musculature tends to improve the symptoms. A subacromial steroid and local anaesthetic injection can sometimes help relieve the inflammatory symptoms associated with the rotator cuff tear.

Traumatic tears and degenerative tears that don't respond to non operative measures can be considered for operative management. Depending of the location, size and nature of the cuff tear; open or arthroscopic repair can be performed after freshening the footprint insertion. Cuff tear appraisal intraoperatively w.r.t the cuff mobility and direction of tear gives useful information regarding the repair. The repair can be performed with anchors or tranosseous suture techniques.
The period of rehabilitation following surgery with physiotherapy is prolonged and the recovery period can be between three to six months after a rotator cuff repair.

Complications

If untreated, massive cuff tears can lead to cuff tear arthropathy in the long run. There can be anterosuperior escape of the humeral head due to the unopposed pull of the deltoid in the absence of the rotator cuff force couple.  
Surgical complications of rotator cuff repair include failure, re tear, prolonged rehabilitation, persistent weakness, and stiffness in the shoulder. 

Controversies

Management of irrepairable cuff tears generally depends on the age. In the elderly low demand patients, a reverse total shoulder arthroplasty yields satisfactory results. In the younger patients, the options are controversial and currently there is no clear evidence. Various options like Cuff tear arthropathy head hemiarthoplasty, muscle/ tendon transfers, autografts ( fascia illiaca), allografts ( synthetic), superior capsular reconstruction, balloon interposition arthroplasty and shoulder fusion have been described. A total shoulder arthroplasty if performed for a cuff deficient shoulder will result in failure of the glenoid component secondary to the rocking horse phenomenon. 

Key take home messages
Anterior footprint of supraspinatus is the commonest area of rotator cuff tear due to its poor vascularity
Not all rotator cuff tears(defects) need surgical intervention
Early diagnosis of post traumatic cuff tears is essential, and one should have a lower threshold for surgical repair if not responding to symptomatic management
There is currently no difference in open or arthroscopic rotator cuff repairs.
UK cuff study suggested that there is more than 85% improvement in shoulder symptoms following a cuff repair.