Shoulders: Mobility vs Stability

The shoulder joint has the greatest range of MOBILITY of any joint in the body; at the expense of this, can be the STABILITY of the joint. Its hard to think of many times throughout the day where you are not using your shoulder joint to some level. Your shoulder is a slave to your hand, so if you are using your hands, you are using your shoulder.

The shoulder joint is stabilised by a labrum (cartilage type soft tissue, drawing the arm into the socket; its capsule (compromising a series of ligaments that connects the arm to the socket) ;and of course the surrounding muscles. Many people who present with shoulder pain blame the “rotator cuff”, and whilst not all shoulder issues are caused by the rotator cuff, there is always a rotator cuff involvement, and – despite the name – this group of 4 muscles (supraspinatus, infraspinatus, teres minor, and the subscapularis muscle) are major stabilisers of the joint. Its very rare – in my opinion – that these muscle need lengthening.

Severe shoulder instability means the shoulder can dislocate (or subluxate) repeatedly during active movement or exercise. The most common dislocation – thought to be around  90-95% – would be an anterior dislocation, where the head of the humerus comes forwards out of the socket.

Subluxate means the joint moves more than it should do in normal circumstances but doesn’t actually come out of joint.

If you have history of previous subluxation or dislocation there is a strong chance of a secondary condition; either a bankart lesion or – more commonly – a hills-sachs lesion.

Bankart Lesion is a lesion of the front part of the labrum of the shoulder, and is caused by repeated anterior shoulder subluxations. This dislocation of the shoulder joint can damage the connective tissue ring around the glenoid labrum.,…

Hills-Sachs Lesion is a compression fracture or “dent” of the humeral head, associated with instability or dislocation at the front of joint. This lesion is caused by an anterior shoulder dislocation which causes the aforementioned dent. A study found Hill-Sachs lesions in 65% of acute dislocations and 93% in patients with recurrent instability (Ref 1)

Both of these lesions can cause further instability, meaning future dislocations are more likely; many people will know what this feels like – “my shoulder always pops out”!

Strong shoulder muscles are our best defence against shoulder dislocation and subluxation caused by instability. The key is to balance the muscles around the shoulder; imagine the head of your arm being on a pulley – front to back. We spend a vast proportion of our day with our arms in front of us; driving, writing, at the laptop, swimming, cycling, bench-pressing. We need to ensure that it is not just the muscles we see in the mirror that are strong.

REFERENCES:

  1. http://www.orthosurgery.gr/dimosieusis/AComparisonoftheSpectrumofIntra-articularLesionsinAcuteandChronicAnteriorShoulderInstability.pdf

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