Australian Papers - Shoulder Impingement Part 3

Abstract

In previous discussions, I referred to incidents of sudden onset shoulder pain, which, in many cases were medically examined, and diagnosed as a rotator cuff injury, sometimes with a recommendation for corrective surgery. the possibility that such shoulder pain could stem from another set of circumstances – not related to the rotator cuff – was rarely considered. This series of technical papers  examines this alternate cause of shoulder pain, which is (a) easy to diagnose, and (b), simple to correct. This paper deals with the ideal performance of an uninjured shoulder assembly from a muscular aspect.

Here are three posterior views of the shoulder assembly, depicting gleno-humeral abduction at the skeletal level; firstly, at rest, secondly at about 45 degrees of abduction, and thirdly at about 100 degrees. The point of interest to us at this stage, is that as the humerus moves past the horizontal, the scapula must commence its downward rotation, to avoid impingement of the tubercle against the acromion.

This, I would stress, is the desired, everyday, and ideal series of events.

These next images suggest what should be happening from a muscular aspect; as the humerus is abducted, perhaps under the power of the lateral deltoid and/or the supraspinatus – the exact nomination of the power unit(s) is not important, all is comfortable.

This first view is at about 45 degrees of abduction, and the scapula remains at its neutral or at-rest position.

Levator and rhomboid are idle.

This second view, as the humerus approaches the horizontal, suggests that the scapula might already be preparing to rotate downwardly, initiating a stretch of muscles such as levator and rhomboid.

Remember, this is my version of normal shoulder assembly function.

The final image in this set displays almost complete gleno-humeral lateral abduction, and some things are worth noting.

Deltoid and supraspinatus are at the end of their contraction tasks, while levator and rhomboids are significantly stretched.

The scapula has completed its downward rotation journey, and we can see the fourth joint in the shoulder assembly – the scapulo-thoracic – in full flight.

This brings me back to the topic of this series of discussions: shoulder pain, that is often diagnosed as a rotator cuff fault.  If the scapulo-thoracic joint (ST) is somehow impeded in its function – if it is unable to rotate downwards, then impingement of the tubercle against the acromion is inevitable, and this event has nothing to do whatsoever with the rotator cuff mechanism

I’ll speculate in later chapters about what damage could occur in the event of impingement – there are  several items of soft tissue in the impingement collision zone; here is a simple shoulder model with artificial ligaments surrounding the GH joint.
What is not shown is the sub-acromial bursa and the supraspinatus muscle – just two other possible casualties.

Well, spring has certainly arrived in my home town of Newcastle, Australia; these are two views of the entrance to Newcastle Harbour – a busy commercial port, at about 10am yesterday, early September.

BERNARD SCULLY,
SEPTEMBER, 2011