Multi-directional Instability of the Shoulder

Instability of the shoulder in multiple directions is moderately often encountered, occurring normally on both sides of the body and is not related to accident or injury. The underlying difficulty is the laxity of the capsule of the shoulder and the deficiencies of these stabilising ligamentous structures. This ligament laxity shows itself in excessive joint mobility in all anatomical directions. Patients may describe joint instability as the shoulder may sublux (partial dislocation) or wholly dislocate from time to time. However, the patient may not suffer such obvious symptoms and complain only of pain.

Conservative treatment is the first line of management for this condition, with physiotherapy treatment consisting of strengthening of the muscular parts of the scapular stability and rotator cuff systems. Once conservative treatment has been attempted and not been successful then consideration can be given to surgery. Surgery can tighten up the shoulder capsule, increasing the strength of the static stabilisers. Typically surgery has been done in open technique but arthroscopic technique is become more prevalent.

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:

* Trauma involved in the cause

* Unidirectional instability - only in a single direction

* Bankart lesion (damage to the rim around the shoulder socket)

* Surgery

TUBS summarises the typical shoulder picture which results from single or multiple episodes of shoulder dislocation.

The instability type which is multidirectional is given the acronym AMBRI which stands for:

* Atraumatic onset (no injury or accident 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.

Thinking about the stability of the shoulder it is helpful to concentrate on a few concepts. The idea of balance is related to the way the head of the humerus centres itself on the socket accurately. The main muscles responsible for maintaining this anatomical alignment are those of the rotator cuff, keeping the joint in line as the larger movement muscles do their actions. If an imbalance or weakness develops in the muscles of the scapula or the rotator cuff then the balance can be disturbed. A cartilage rim around the socket, the glenoid labrum, deepens the socket and the muscles compress the two parts together, enhancing stability.

An upward movement of the humeral head on the socket is undesirable and this tendency is resisted by the compressive force of the rotator cuff and by the curve of the upper socket area. The joint surfaces have some adhesion as they are wetted by the synovial fluid, with air being pressed out of the joint by the tight fit of the rounded ball and the depth of the socket, creating a degree of suction effect to enhance stability. Some amount of negative pressure which develops in a tight joint also adds to the effect. The stability which is improved by these effects is in the mid-range of the joint's movement, where there is least stability from the ligaments.

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.

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Jonathan Blood Smyth is the Superintendent of Physiotherapists at an NHS hospital in the South-West of the UK. He writes articles about back pain, neck pain, and injury management. If you are looking for physiotherapists in Manchester visit his website.

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