The shoulder is a strange joint. It is actually three joints–the gleno-humeral (or ball and socket) joint, the acromio-clavicular joint (where the collar bone attaches to the shoulder), and the scapulo-thoracic joint (where the shoulder blade moves on the back of the rib cage).
The unique configuration of the shoulder allows amazing motion and permits us to position our hands in all sorts of ways. The complexity of the shoulder and the ways we constantly use it can lead to injury, however. One of the most notorious ways the shoulder can cause problems is an injury to the rotator cuff.
The rotator cuff is a group of four muscles and tendons that help keep the humeral head (the ball) centered on the glenoid (the socket). The ball is large and the socket is relatively flat and small so the bony anatomy of the shoulder is like a golf ball on a golf tee, or like a teacup on a small saucer. The only thing keeping the ball next to the socket is a balance of muscle forces, where the rotator cuff muscles push the ball down and into the socket, keeping it centered so the larger muscles around the shoulder can move it.
Sometimes, with repetitive overhead activity or an injury, the top tendon of the rotator cuff, the suprapinatus, can come into contact with the bottom of the bony shelf, the acromion, which lies over the top of it.
This is more likely if there is a spur or hook shape on the acromion. This can cause irritation to the covering of the tendon, the bursa, a fluid filled sac. When the bursa becomes irritated, it swells and the lining thickens, decreasing the space available for the tendon to move under the bony shelf. What this causes is further rubbing of the tendon and the bursa, especially with certain motions of the arm such as overhead activities or reaching behind the back. The rubbing further irritates the bursa and tendon, causing further swelling and irritation, thickening the bursa and making further rubbing more likely. This becomes a painful cycle which can be difficult to break.
Impingement can sometimes evolve into a spectrum of rotator cuff problems. In other words, what starts out as a bursitis can become a tendonitis, and, with progressive rubbing, can turn into a partial or full thickness hole in the tendon–a rotator cuff tear. In general, the longer the symptoms have been present, the greater the risk of progression to full thickness tear.
Treatment of impingement syndrome depends on the amount of damage done to the rotator cuff. In it’s early stages, treatment can consist of oral anti-inflammatory medicines and rotator cuff rehabilitation exercises. If a thick, inflamed bursa is present a injection of a cortico-steroid such as Depo-Medrol can be very helpful to reduce the swelling and break the cycle. Physical therapy is a vital part of treatment and is essential for maintenance of good rotator cuff function. If the rotator cuff is significantly torn or compromised, surgery (usually arthoscopic) can be required to re-attach the tendon and eliminate bone spurs and inflamed bursa.
The tendons of the rotator cuff can tear either by the impingement mechanism outlined above or, more commonly, thru age related degeneration of the tendon. Like an old rope left out in the sun, the tendon can become more brittle and small tears can occur, usually on the underside of the tendon. These small tears put more strain on the fibers remaining intact and they they too start to fail like an expanding hole in a sock. If the tear is left untreated, it may eventually progress to a massive, un-repairable tear. In this instance the edge of the cuff retracts so far that it cannot be brought back over to it’s original insertion site. The torn tendon also atrophies, or turns into scar tissue, so even if it can be re-attached it may never work as a normal muscle or tendon again.
Because of the poor natural history of rotator cuff tears, surgery is usually recommended for a painful full thickness tear or large partial thickness tear. This can usually be done arthroscopically. If the tear is very large or the tissue is poor, open surgery to supplement the weakened cuff with a graft is sometimes necessary. Based on pre-operative planning studies, such as the MRI, we can usually predict which approach will be needed.
Click on the topics below to find out more from the Orthopaedic connection website of American Academy of Orthopaedic Surgeons.