Shoulder Instability in Multiple Directions
The condition of the shoulder suffering from instability in many different directions is encountered moderately often, happening in both shoulders and unrelated to any physical incident. The lax nature of the capsular bag around the shoulder is the reason that these instability problems are occurring. The high degree of anatomical joint mobility is an indication of the lax nature of the shoulder ligaments and capsule, with patients describing an unstable joint which might dislocate or at least partially do so (subluxate). Obvious joint abnormalities are not always present and patients may just complain of pain.
The mainstay of treatment is conservative management, with physiotherapists working on increasing the strength of the stabilising muscular systems such as the rotator cuff muscles and the scapular stability muscles. If conservative rehabilitation is not successful then surgical intervention can be undertaken to stabilise the more static stabilisers such as the shoulder capsule, tightening up so that stability is increased. Open surgery is the typical technique but arthroscopic techniques are developing rapidly.
How common this pathology is in the overall population is not clear and it is much more common to have instability of the shoulder from traumatic events such as incidents which lead to shoulder dislocation. In this field there are several different classifications, TUBS stands for:
* Traumatic onset
* Unidirectional instability – only in a single direction
* Bankart lesion presence – this is injury to the cartilage rim around the socket
* Surgery – which is often required
A single or repetitive dislocation of a shoulder joint traumatically can lead to the generalised instability problem described in TUBS.
AMBRI is the acronym which summarises the other type of dislocation, the multidirectional form:
* Atraumatic – there was no accident or injury to explain the onset
* Multidirectional – the shoulder is lax in all directions
* Bilateral – both shoulders are typically affected
* Rehabilitation is the first line of treatment with a physiotherapist
* I refers to the technical types of surgery and where they are performed.
The shoulder joint exhibits a high level of joint mobility to allow it to participate in placing the hand in many potential places in space, in front of the eyes so we can see what we are doing. This mobility is at the cost of stability, so the shoulder fails to be sufficiently stable under certain conditions.
In considering what stability of the shoulder means it is useful to think about various concepts. Balance is the concept that the head of the humerus should be centred on the centre of the glenoid socket. The rotator cuff muscles are the main controllers of this positional requirement, allowing the shoulder to be moved around by the large nearby muscles. If the rotator cuff muscles or the muscles stabilising the scapula weaken this can alter the ability to maintain balance. The muscles compress the head into the socket which is made deeper by the labrum, the cartilage rim around the socket.
The upper half of the shoulder socket adds to the resistance against upwardly movement of the head of the humerus which the rotator cuff also provides by its compressive function. Synovial fluid makes the joint surfaces wet and so they adhere to each other to a degree, the convex ball and the concave deepness of the socket combining to push any air out and create an amount of suction force holding the joint in place. A tight joint typically has a degree of negative pressure and this helps it hold together too. These methods of enhancing stability work in the mid ranges of the joint, the parts of the joint range where the ligaments are least effective.
The capsule of the joint is a passive structure which keeps the shoulder movement within certain limits, with the shoulder ligaments being thickenings of the capsule at important areas to resist the forces applied. The most important ligamentous restraint is the inferior glenohumeral ligament; however the dynamic parts of the stability system, the muscles, are also of great importance. Physiotherapists concentrate on rehabilitating scapular stability and the function of the rotator cuff to improve shoulder stability.
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about physiotherapy, physiotherapy, physiotherapists in Leeds, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.