// Common injuries - Shoulder impingement

by Paul Wright

Pain in the shoulder region is a common problem for personal training clients and athletes alike. A number of individual conditions can lead to a painful shoulder, but this article will focus on pain caused by impingement.

WHAT IS IMPINGEMENT?

Impingement is the term used to describe the ‘pinching’ or ‘jamming’ of tissue between the acromion (the end point of the scapula) and the humerus. This jamming usually occurs as the arm is abducted at the shoulder. Chronic impingement can lead to a swelling of the affected tissues and a further reduction in the size of the space between the acromion and the humerus (this space is referred to as the subacromial space), with pain typically felt in the anterior or lateral aspect of the shoulder.

In their excellent text Clinical Sports Medicine (essential reading for all personal trainers and therapists), sports physicians Peter Brukner and Karim Khan make the very valid point that the term ‘impingement’ relates to a clinical sign and is not to be used as a diagnosis. They also describe impingement as either external (primary or secondary) or internal, as defined below:

Primary External Impingement – abnormalities of the superior structures such as a beaked or curved acromion that encroach into the sub acromial space – common in the over-35 age group.

Secondary External Impingement – this involves encroachment from above in the younger athlete (under 35) due to poor scapular control, glenohumeral instability (leading to rotator cuff fatigue), and imbalance between the deltoids and rotator cuff muscles.

Internal Impingement – this occurs in overhead athletes during the extremes of the ‘cocking action’ in throwing – i.e., abduction and external rotation – when the undersurface of the rotator cuff is pressed against the posterior-superior surface of the glenoid fossa (the socket of the scapula). Brukner and Khan make the point that this internal impingement is a normal process, however the volume and intensity of this ‘cocking action’ in overhead athletes leads to repetitive microtrauma and eventually leads to tissue failure and pathology.

FACTORS LEADING TO THE DEVELOPMENT OF IMPINGEMENT
 
A) ANATOMICAL ABNORMALITIES
Some individuals possess specific anatomical factors that can contribute directly to the development of impingement. A pointed end to the acromion or an extra piece of bone coming off the undersurface of the acromioclavicular joint can effectively decrease the subacromial space. Anatomical abnormalities fit into the classification of Primary External Impingement.

B) POOR SCAPULAR CONTROL
It is essential that the scapula and humerus move in a coordinated way during shoulder joint motion – this is called scapulohumeral rhythm. Poor scapular control can lead to a forward and downward movement of the acromion, which will reduce the subacromial space and increase the chance of impingement. Poor scapular control fits into the classification of Secondary External Impingement.

C) INSTABILITY
Unlike the hip joint, the glenohumeral (or shoulder) joint only has a shallow socket and it is common for the humerus to slide excessively during shoulder movement – this excess motion is called instability. The rotator cuff muscles are essential in controlling instability as they pull the humerus down and into the socket. Should the rotator cuff muscles become fatigued there is nothing to prevent the strong deltoids and pectorals from lifting the humerus into the acromion. Instability fits into the classification of Secondary External Impingement.

D) POOR BIOMECHANICS
The risk of impingement is greatly increased if the scapula is not able to be positioned or moved adequately during exercise – especially exercises involving the arm overhead motion. A common biomechanical problem is a lack of adequate thoracic spine extension and rotation. This lack of motion in the spine causes the acromion to be forced down and forward with exercise, thus reducing subacromial space.

PREVENTION AND TREATMENT OF IMPINGEMENT

In all cases of shoulder pain it is essential that a comprehensive examination be performed by a physiotherapist or sports physician – this will ensure a correct diagnosis as well as excluding other possible causes of pain such as referral from the cervical spine. Once the diagnosis is made and other conditions excluded, a treatment plan will be instigated and overseen to ensure effective return to activity.

A) ANATOMICAL ABNORMALITIES
The only way of confirming these abnormalities (such as a beaked acromion) is with X-ray investigation. Be aware, however, of clients with old AC joint injuries as they may have bony changes that also reduce the subacromial space.
If you do have a client with impingement and they are known to have these anatomical changes, it is essential that you reduce the amount of overhead activities in their program – this will reduce the amount of impingement and limit tissue damage. It is also important to encourage thoracic spine extension and rotation to effectively unload the shoulder. Some excellent thoracic spine mobility exercises are the fitball pullover and the standing cable row (see photos 1 and 2).

B) POOR SCAPULAR CONTROL
The best time to observe scapulohumeral rhythm is during the performance of common exercises such as push-ups, rows and pulldowns. It is vital that the trainer check that the scapula moves in a smooth and controlled manner, compares right to left, and ensures that the acromion does not drop forward and down during the performance of the exercise. It is also useful to look for ‘winging’ of the scapula where the inferior border lifts up and away from the ribs – this is best observed in the push-up.

In most physiotherapy-designed rehabilitation programs the starting point is to retrain the scapular stabilisers before moving on to work with the rotator cuff – this allows a solid and correct base to be established before embarking on more functional rehabilitation. Some useful scapular control exercises include the towel squeeze and the medicine ball wall throw (see photo 3).

C) INSTABILITY
Signs of potential shoulder instability include a history of a dislocated or subluxed shoulder, clicking or clunking of the shoulder, or general hypermobility in other joints. The importance of rotator cuff exercises cannot be over-emphasised, and they are an essential component of all training programs.

The most obvious way to improve instability it to increase strength of the rotator cuff muscle group (the supraspinatus, infraspinatus, subscapularis and the teres minor). Most trainers should have a solid bank of rotator cuff exercises at their disposal – from the simple cable external rotation and internal rotation movements to advanced drop catching exercises – but it is often difficult to convince clients to perform rotator cuff exercises as these muscles are deep stabilisers and cannot be seen. For the reluctant client it may be worth mentioning that significant increases in bench press strength are linked to improved rotator cuff function – it’s worth a try.

D) POOR BIOMECHANICS
A simple test for thoracic spine extension (a common biomechanical limitation leading to shoulder dysfunction) involves asking the client to sit on the edge of a bench and raise both arms as far as possible above their head. If they cannot get at least 170 degrees of shoulder flexion they should not be given overhead exercises. It is also important to include exercises which encourage thoracic extension and rotation – e.g., ball pullovers and standing one arm cable rows.

In the case of athletes, there may also be some limitation in techniques in their sport that need to be addressed during their sports coaching sessions. Examples of sports technique modification to reduce shoulder stress include increased body roll in freestyle swimming, modification to the ball toss in the tennis serve, and improving the follow-through in cricket fast bowlers. This is where it is vital that the fitness trainer work with the technique coach to ensure that all support staff are working together to ensure safe performance. 


Paul Wright, BAppSc (Physio) DipEd (PE)
Paul is the owner of Get Active Physiotherapy with clinics inside Fitness First clubs at St Leonards (Sydney) and Kotara (Newcastle) as well as a head office in the CBD of St Leonards. He has produced a series of injury prevention and training DVDs for fitness professionals, including a session on shoulder injury rehabilitation. For more information visit www.getactivephysio.com.au or call 02 9966 9464.



NETWORK • SPRING 2008
• PP32-33