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Shoulder impingement syndrome is caused by pinching the supraspinatus tendon (part of the rotator cuff) and bursa (lubricating sac) between the upper arm bone (humerus) and the acromion. The bursa and upper arm bone are part of the scapula (shoulder blade) and together they form the roof of the shoulder. The bursa functions as a cushion, preventing the acromion and the rotator cuff tendons from grinding against each other.
If the shoulder blade is not held in a neutral position (ie if you have bad posture) the space between the two bones is reduced. Repetitive movements of the shoulder joint will therefore lead to increased friction and mechanical pinching (impingement) of the soft tissues (tendons and bursa).
Some people are predisposed to impingement syndromes as they have curved acromions leading to a reduced subacromial space (the space under the shoulder roof) from the outset.
If the rotator cuff muscles are not working effectively to centre the ball within the socket, the ball will move about in an uncontrolled fashion, again causing an increased impingement of the bursa and tendon.
Constant or repetitive impingement will cause the bursa to swell, leading to bursitis, or the tendons to fray, resulting in tendinopathy, both of which further reduce the space between the two bones (subacromial space) and a vicious cycle begins. Long-term impingement can significantly increase the likelihood of developing a rotator cuff tendon tear.
Pain is the most common primary complaint, and it is often noted through an arc of upper limb movement, pain often reducing as the arm reaches full elevation. Sudden movements also reproduce a sharp catching pain, making upper limb functional activities very uncomfortable.
So what can be done?
In their Cochrane Review, Buchbinder et al (2003) supported the early use of steroid injection stating:
“The available evidence from randomized controlled trials supports the use of subacromial corticosteroid injection.”
Short-term use of NSAID (anti-inflammatory) medications can also be of use, along with activity modification (rest) and ice.
Careful assessment of an individual’s biomechanics by a physiotherapist allows for the implementation of a specific tailored exercise program, aimed at improving the subacromial dimensions and reducing the potential for ongoing pathology. The program will often include some or all of the following:
- Postural/scapular control exercises;
- Thoracic mobility exercises;
- Rotator cuff strengthening exercises; and
- Capsular/Cuff stretching.
Severe impingement syndromes that do not settle with appropriate conservative therapy may require surgical decompression (accromioplasty). Interestingly, a recent study by Kromer et al (2009) showed that physiotherapy lead exercises were as effective as surgery in the long term.
Buchbinder, R., Green S. and Youd, J.-M. Corticosteroid injections for shoulder pain. Cochrane Database of Systematic Reviews 2003, Issue 1. Art. No.: CD004016. DOI: 10.1002/14651858.CD004016.
Thilo, O., Kromer, M., Ulrike G., Tautenhahn, M., Rob A., de Bie, J., Bart S., and Bastiaenen, C. Effects of Physiotherapy in Patients with Shoulder Impingement Syndrome: A Systematic Review of the Literature. Journal of Rehabiliation Medicine 2009; 41: 870–880