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.

Shoulder instability is initially treated conservatively to attempt to increase the muscular stability with physiotherapy used to increase the strength of the rotator cuff muscles and scapular stabiliser muscles. If physiotherapy and other conservative management have been tried without much success then surgery is targeted at improving stability in the passive joint constraints such as the shoulder capsule and related ligaments. Arthroscopic surgical technique has rapidly improved to take over the older open methods.

How many people in the population suffer from multidirectional instability is not known and a much more common situation is to acquire instability of the shoulder due to an accident or incident which results in dislocation. TUBS is an acronym for this problem:

* Traumatic cause

* Unidirectional instability (only unstable in one 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.

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

* Atraumatic cause – no injury or accident

* Multidirectional – all the shoulder ranges of movement are lax

* Bilateral – both shoulders are always involved due to general laxity

* Rehabilitation used as the initial management

* I stands for the techniques of surgery and where this is performed.

The shoulder joint has a very high degree of mobility and is designed to allow us to place our hands where we want to within our visual fields, enabling us to perform actions while we watch. We have sacrificed stability of this joint for its mobility, leading to consequent problems when the shoulder is stresses in various ways.

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.

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 joint capsule acts passively to hold back excessive movement of the shoulder and keep it within safe limits, with thickened areas of the capsule developed into the ligaments of the shoulder, the most important of which is the inferior glenohumeral ligament. This does not mean that the muscles, the dynamic stabilisers of the shoulder system, are not very important in the normal function of the shoulder. Physiotherapy concentrates on strengthening and re-educating the rotator cuff and scapular stability muscles.

Jonathan Blood Smyth is the Superintendent of Physiotherapy 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 Sheffield visit his website.