Impingement

Shoulder impingement is not a diagnosis, it is a symptom. When we talk of impingement there is a catching or pinching of structures underneath the Acromioclavicular joint (joint on top of the shoulder where the collar bone meets the shoulder blade).
Any one or more of a number of structures can get pinched in this space. Usually one of two structures are involved. Most frequently it is a tendon of the rotator cuff. The rotator cuff is a group of four muscles coming from the spine and shoulder blade. They wrap around the shoulder joint to suck the ball of the shoulder into the socket of the joint. They give stability to the joint and are also involved in the movements of the arm particularly rotation as the name would suggest.


The tendon that is most exposed in the rotator cuff is the supraspinatus tendon. This tendon lifts the arm away from the body and helps rotate it away from the body. When the arm is lifted overhead the tendon can become squeezed between the shoulder joint and the Acromioclavicular joint on the top of the shoulder. If this happens once or twice it is not a great problem. Repeated catching of this tendon will cause it to become inflamed. That results in a tendonitis making the shoulder painful, weak and increasingly stiff.
If the tendonitis is not treated early it can cause a chronic impingement of the shoulder. Prolonged inflammation will weaken the tendon and could eventually cause the tendon to fray or tear. The tendon can also be torn as a result of trauma such as a fall on an outstretched hand or onto the shoulder. If the arm is suddenly forced backwards or rotated this could also tear the tendon or by lifting something too heavy or repetitive overhead lifting. A torn rotator cuff tendon is a painful and debilitating injury that can take months to years to resolve.
It is important to ask why the tendon would become squeezed between the shoulder and AC joints in the first place. Normally there is enough space between these joints for the arm and tendons to function properly. So what would cause the space to narrow? The most common reason is posture. If you allow your shoulders to slouch forward as when sitting at a PC or folding your arms in front of your chest, this will narrow the joint space. This is a gradual process and slowly causes the shoulders to become rounded and will eventually cause an impingement. Another possibility is degenerative wear and tear of the AC joint. If the AC joint becomes worn, Small boney projections called osteophytes can protrude from the joint. These act like little daggers into the soft tissues under the joint. Both of the scenarios above will result in a shoulder impingement.
The other structure in the Acromioclavicular joint space that gets squeezed is the sub acromial bursa. This is a fluid filled sack much like an airbag that sits between the rotator cuff and the point of the shoulder. It is there to act like a shock absorber in the joint. If there is repetitive squeezing of the bursa it can slowly become inflamed. It will also become acutely inflamed as a result of direct trauma such as a fall onto the arm compressing the joint or if something falls onto the shoulder from above.
The swollen bursa will reduce the space between the shoulder joint and the Acromioclavicular joint and will be squeezed or pinched when the arm is raised. This also causes an impingement syndrome.
Depending on the source of the impingement there are different ways to treat the problem. Firstly it is important to establish the correct diagnosis. The physiotherapist has a number of clinical tests they can carryout to help achieve this. If they are unsure or need to confirm the diagnosis it may be necessary to carry out other tests. An x-ray of the shoulder can identify or rule out the possibility of an osteophyte. An MRI scan may be able to establish a tear in the rotator cuff or a swollen bursa. Ultrasound scans are also useful to see the rotator cuff in various positions as it is possible to move the shoulder while carrying out an ultrasound scan. This is not possible when performing an MRI scan. One or more of these tests may be required to finalise a diagnosis.
Once the correct diagnosis is established the treatment begins. An acute tendonitis can be treated with Ice, anti-inflammatories and an exercise program. A traumatic rotator cuff tear needs to be placed in a sling and rested for about 3 weeks. Also during this time the physiotherapist will work on the tendon to prevent the formation of scar tissue and then rehabilitate the shoulder girdle complex when appropriate.
A bursitis may need a cortisone injection to kill the inflammation but the physiotherapist can normally reduce the pressure on the bursa by mobilizing the joint and strengthening the shoulder. Impingements as a result of posture or osteophyte formation need a lot of work on improving posture and mobilising the Acromioclavicular joint to improve joint space. The underlying tendonitis or bursitis also needs to be treated and the shoulder rehabilitated.
If conservative management is not effective then other interventions such as injection therapy or surgery are available. Most surgeons will tell there patients to try conservative management for at least 3 months before resorting to surgery and will often insist on waiting a year before operating. The earlier treatment begins the greater the success.