Instability of the shoulder means an inability to keep the humeral head (ball of the joint) in glenoid fossa (socket of the joint). You may feel that the ball of the joint is slipping, catching or even coming out of the socket. The ligaments and muscles around the shoulder joint create a balanced environment to make the shoulder most mobile joint in your body.
There are 2 different types of instabilities that cause disruption to this balanced environment. The instability can occur anterior (towards the front of the shoulder), posterior (backwards), inferior (downwards to your armpit) or a combination of these three.
As the name implies there must be a traumatic incident to your first dislocation. Most commonly happens in contact sport. Out of all types of instability, anterior instability following a trauma is the most common one comprises more than 90%!
Usually the ball is forced forwards and downwards. Commonly the ligament in the front of your shoulder is over-stretched and can pull part of the rim of cartilage off the socket. If the cartilage is detached in this way it is called a ‘Bankart lesion’ (click here to see more information). It is sometimes detectable with an MRI (Magnetic Resonance Image) scan but may only be visible when the surgeon looks in your shoulder joint at surgery. Surgery is indicated when it become unstable with lightest of the movements. Sometimes you can have a dent in the back of the ball of the joint which is formed as the ball is forced out of the socket. This is known as a ‘Hill-Sachs lesion’ this will mostly picked up on an X-ray.
It is a sub classification of glenohumeral joint (ball and socket -shoulder joint) instability, a clinician may put you under this category if there is no history of a trauma to cause the dislocation.
Atraumatic is again sub-divided into two main types:
May be seen after surgery for shoulder dislocation, due to glenoid rim lesions. Over time, microtrauma can lead to instability of the glenohumeral joint. This type is common in people/athletes who perform repetitive overhead movements.
Your Physiotherapist at Pure or your GP will be able to tell you if your shoulder joint is unstable by doing some simple clinical tests and taking accurate history of symptoms from you. However, sometimes an X-ray will be done and very occasionally an MRI scan will be ordered, to see if there is any damage to the rim of cartilage and/or bone.
There is strong evidence to suggest progressive strengthening of the shoulder can be helpful in both traumatic and atraumatic instability. Your Physiotherapist at Pure can help you with this and it is also important that you have some education on condition, posture and motor control, especially by strengthening your rotator cuff muscles. However, if the movement is good and muscles are working well, but the joint is dislocating or slipping regularly and stopping you doing what you want to do, your Doctor or Physiotherapist may refer you to a Specialist Orthopaedic Surgeon for consideration.
There are several types of shoulder operations that stabilize the shoulder.
Please note that you may have to undergo a progressive long term rehabilitation with a Physiotherapist, under surgeon’s protocol.
Barrett, C. (2015). The clinical physiotherapy assessment of non-traumatic shoulder instability. Shoulder & elbow, 7(1), 60-71.
Cuéllar, R., Ruiz-Ibán, M. A., & Cuéllar, A. (2017). Suppl-6, M10: Anatomy and Biomechanics of the Unstable Shoulder. The open orthopaedics journal, 11, 919.
Tzannes, A., & Murrell, G. A. (2002). Clinical examination of the unstable shoulder. Sports Medicine, 32(7), 447-457.