The rotator cuff is a group of four muscles which attach throughout the surfaces of the shoulder blade (scapular). They run horizontally and converge with the soft tissue capsule of the shoulder joint and attach to the top and side of the top of the upper arm bone (humerus). As with all muscles, as the rotator cuff muscles get nearer their attachment site their anatomy changes to become tendon tissue. Tendons are a thick band of strong connective tissue which act as an anchor of muscles to their attachment.
A rotator cuff arthropathy describes pain and weakness to the shoulder joint as a consequence of initial dysfunction to the rotator cuff tendons. Dysfunction to these tendons is thought to be a result of age-related changes to the tendon which are commonly exacerbated with a trauma such as a fall which leads to an extensive rotator cuff tear.
The shoulder joint is formed by a small, relatively flat socket (glenoid) which the upper arm bone sits in. The design is to allow the large range of motion that the shoulder requires for full function. This design places a far greater demand on the muscular support system to stabilise the shoulder joint and provide adequate power to move the shoulder under load. The rotator cuff muscles and tendons are key to this support system.
The four rotator cuff muscles form a sling around the shoulder joint and each provides force to move the shoulder joint in a specific way:
- Supraspinatus: lies to the top of the shoulder and aids lifting the arm to the side and front.
- Infraspinatus: lies to the top and back of the shoulder and provides strength in external rotation.
- Teres minor: lies to the middle and back of the shoulder and provides strength in external rotation.
- Subscapularis: lies to the front of the shoulder and provides strength in internal rotation of the shoulder.
- As a group: when moving the shoulder or lifting load, the rotator cuff tendons all activate to provide a strong compression force across the shoulder joint. This allows the surrounding muscles appropriate leverage to move the shoulder as well as ensuring the upper arm bone remains centred in the centre of the socket (glenoid).
Due to these significant roles in maintaining shoulder joint function, a rotator cuff arthropathy often leads to other secondary problems including:
- Extensive tearing and often retraction of the rotator cuff tendon(s)
- Shoulder joint degenerative change (osteoarthritis)
- Reduced distance in the sub acromial space at the top of the shoulder joint
Due to the causes being largely related to degenerative changes to the rotator cuff tendons and shoulder socket a rotator cuff arthropathy will normally affect individuals over 60 years old. It may present in younger individuals if there has been significant trauma to the shoulder or if they suffer with other medical problems which affect their general health.
The most notable feature of a rotator cuff arthropathy will be shoulder pain on attempting to move the shoulder. Often the pain will also be present through the night when lying on the side. An inability to lift the arm to and above head height will occur due to an inability to create tension across the joint due to the torn tendons.
Due to the pain, inflammation and inability to use the arm adequately, if left untreated, a shoulder suffering with a rotator cuff arthropathy will suffer a gradual reduction in range of motion.
Due to the significant structural problems associated with a rotator cuff arthropathy, to restore shoulder function then surgery will normally need to be considered. However, for medical and for other personal reasons many patients will prefer to continue with a non-surgical approach which can still provide some improvements.
Physiotherapy exercises to retain shoulder range of motion and prevent contractures from developing as well as a program of strengthening exercises to optimise the function of remaining shoulder muscles without an in tact rotator cuff are the mainstay. In some cases, this may allow some improved but sub-optimal function such as being able to reach to the head without being able to fully elevate the arm.
If pain is a limiting factor in being able to complete a program of exercises or in cases where there is significant nocturnal pain corticosteroid injections may be considered to provide a powerful anti-inflammatory effect.
When surgery is considered this involves implanting a shoulder replacement. In most cases of a rotator cuff arthropathy an "anatomical reverse shoulder prosthesis" will be used. This form of prosthesis reverses the normal shape of the shoulder and inserts the prosthetic socket in to the upper arm and the ball part of the joint in to the end of the shoulder blade. This clever design allows the remaining muscles and tendons to produce force and move the shoulder without the rotator cuff tendons.