Changing upper body posture is believed to change the development of subacromial impingement syndrome. Suggesting that if a thoracic kyphosis angle as well as an altered scapula position is prevented the compression in the subacromial space will not occur thus avoiding an impingement.

What is impingement?

Singularly or in combination different mechanisms can contribute to subacromial impingement syndrome; inflammation and degenerative changes of tendons, weak or dysfunctional rotator cuff and scapular muscles, posterior glenohumeral capsule tightness and postural dysfunctions of the spinal column and scapula.
There are three different categories of impingement; primary, secondary and internal. Primary impingement is the compression of the rotator cuff tendons between the humeral head   and as stated about the more commonly known mechanism.
Neer outlined 3 stages of primary shoulder impingement:

Stage 1: described a process of acute inflammation, oedema, and hemorrhage of the rotator cuff conjoint tendon. This stage affects younger patients normally aged below 25 years of age and is usually reversible with conservative treatment alone.
Stage 2: affects patients between 25-40 years of age and represents a continuation of the process, outlined in stage 1, to a more irreversible form. As the tendon becomes swollen there is increased friction further perpetuating the problem. In this stage, the rotator cuff tendon undergoes fibrosis and tendonitis.
Stage 3: affects older patients usually over the age of 40 years. The key factor in stage is that there is an actual mechanical disruption of the rotator cuff tendon in the form of either partial or complete cuff tears. In this stage, changes also occur in the coracoacromial arch such as osteophyte formation, which may also reduce the subacromial space.

Secondary impingement is thought to occur from primary compressive symptoms becoming secondary to underlying instability of the shoulder. Due to the increased humeral head translation the bicep and rotator cuff tendons can become impinged secondary to instability. Consequently, the effects of secondary impingement can lead to a secondary injury; a rotator cuff tear, if the instability and impingement continue.

The third category is internal impingement, this affects the younger population and is also known as undersurface impingement. This is where the shoulder is placed into a 90/90 position (90 degrees abduction and 90 degrees external rotation) which causes the supraspinatus and infraspinatus tendons to rotate posteriorly. Causing a more posterior orientation which therefore results in the tendons becoming pinched or compressed between the humeral head.

Can changing posture help shoulder impingement syndrome?

As mentioned above postural dysfunctions of the spinal column and scapula are just one of many mechanisms thought to contribute to shoulder impingement.   Different studies have therefore looked into how changing posture will affect the shoulder and if it affects shoulder impingement syndrome.

One study looked at 120 subjects; 60 with subacromial impingement and 60 asymptomatic. They looked at manually taping the thoracic spine and scapular with the intent to change their posture.  The findings of this investigation suggested that changing one or more of the components of posture may have a positive effect on shoulder range of motion and the point at which pain occurs.   They compared this to a placebo procedure and it showed the correctional taping increased shoulder movement in people with and without shoulder symptoms. Another study looked at the effect of slouched versus erect sitting posture on shoulder pain intensity and range of motion in subjects with shoulder impingement. 28 subjects with impingement measured their maximum active shoulder flexion and associated pain intensity in slouched and erect sitting postures, using video-analysis. Results showed that by having an erect sitting posture appeared to increase shoulder flexion but no change in pain intensity.   Therefore, reporting that a reduction in the thoracic kyphosis leads to increased shoulder range of motion. Again, by supporting the fact that altering the mechanical changes in a patient’s upper body can therefore increase shoulder range.

An additional study also investigated if posture was associated with impingement, however this study looked at if forward head posture was associated with an increased thoracic kyphosis and an altered position of the scapula. As it is thought that by having an increase in the thoracic kyphosis angle and a downwardly rotated, anteriorly tilted, and protracted scapula alongside muscle imbalances, an increased compression in the subacromial space occurs.
For this study selected sagittal and frontal plane postural measurements were made in 60 asymptomatic subjects and 60 subjects with subacromial impingement syndrome. The findings suggested that upper body posture does not follow the set patterns described in most literature, and further research is required.  The studies found positive changes in shoulder range or motion however, minimal on pain reductions and subacromial impingement syndrome is associated with pain.
These studies looked at changing posture with the intent of reducing shoulder impingement symptoms or reducing the onset by trying to change posture using different interventions. They looked at shoulder impingement as a whole but, finding a primary cause of impingement is important whether that be overuse or an instability of the shoulder. As mentioned above by Jeremy Lewis et al, posture can affect the development of shoulder impingement. However, by finding the initial cause and grouping impingement into these categories; primary, secondary or internal could help determine what stage the impingement is at and by categorising it could help determine what treatment route they need to go down.

For example subjects who are found with secondary impingement could benefit from postural change as it is thought that these subjects have an underlying instability of the shoulder, which then causes the tendons to become pinched from excessive overhead overuse.  Rather than primary and internal impingement which occur from more overuse and mechanical. Therefore, further research looking into the same interventions, but grouping the subjects into categories; primary, secondary and internal impingement could result in different outcomes as the groups will be more specific to a mechanism and not so general. This would be a time-consuming task however would lead to the more specific treatment of patients.

Current management of shoulder impingement syndrome

It is thought by Smidt and Green that the reproducibility and validity of diagnosis and classification system for the shoulder are insufficient, and that a new method of assessment needs to be considered.  Diagnosing shoulder impingement should include a structed assessment of the patient’s history and specific clinical assessment tests that isolate the affected structure. Only then based from these responses can the diagnostic be completed, and a treatment plan be recommended and carried out.
Lewis J has mentioned a system called the Shoulder Symptom Modification Procedure (SSMP) which looks at selecting a movement or activity that reproduces the patient’s symptoms. This may be from what the patient has identified, from their history or findings from the orthopedic tests (figure 1).   Clinical diagnostic tests such as Hawkins test, Neer test and others play an important part in the clinical evaluation. These tests were found by Calis, M et al to be the most sensitive in diagnostics but have low sensitivity values.  Currently the uses of special orthopedic tests are used as pain or symptom provoking procedure alongside other physical movements that reproduce the patients shoulder pain. Once the movement or activity has been agreed upon the SSMP is applied.

The SSMP is a sequence of four principle techniques applied to a patient while they perform the activity or movement that most closely reproduces the symptoms they are experiencing. Hence why it is so important to identify what and how aggravates the patient’s pain. Once the SSMP has shown which procedure provides the greatest reduction in symptoms, a rehabilitation program can be formulated using similar techniques to the testing procedures. The SSMP process may not work on everyone, and this is then where other treatment methods would take place, such as other methods of rehabilitation, injections or even surgery. The SSMP is a process available to help support a clinical decision by identifying factors that ease a patient’s shoulder symptoms not to be used instead of.

Discussion
In summary, there is no real evidence that suggests posture alone affects the etiology of shoulder impingement syndrome.  Most studies look into changing posture or scapular positioning to help shoulder impingement syndrome. The studies found that by altering the biomechanics of the scapular and reducing a thoracic kyphosis prevents compression of the subacromial space thus increasing shoulder range of motion.

As mentioned above, primary compressive symptoms become secondary to an underlying stability, for example when the joint goes through excessive overuse of overhead activities these therefore can lead to anterior instability of the shoulder.  Hence trying to change the instability through posture or scapular repositioning. Taping the thoracic region and shoulder does not appear to have a placebo effect on pain and range of shoulder movement.   In return shows any changes will be a genuine change and not just a placebo effect. Therefore, resulting in a better understanding of the etiology which will then in turn identify a better understanding of the injury and result in better treatment prescribed.

References (Vancouver/in appearance)

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Lewis J, Green A, Wright C. Subacromial impingement syndrome: The role of posture and muscle imbalance. Journal of Shoulder and Elbow Surgery. 2005;14(4):385-392
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Ellenbecker T, Cools A. Rehabilitation of shoulder impingement syndrome and rotator cuff injuries: an evidence-based review. British Journal of Sports Medicine. 2010;44(5):319-327.
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Lewis J. Rotator cuff tendinopathy/subacromial impingement syndrome: is it time for a new method of assessment?. British Journal of Sports Medicine. 2009;43(4):259-264.
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Lewis J, Green A, Wright C. Subacromial impingement syndrome: The role of posture and muscle imbalance. Journal of Shoulder and Elbow Surgery. 2005;14(4):385-392.
Lewis J, Green A, Wright C. Subacromial impingement syndrome: The role of posture and muscle imbalance. Journal of Shoulder and Elbow Surgery. 2005;14(4):385-392.
Lewis J, Green A, Wright C. Subacromial impingement syndrome: The role of posture and muscle imbalance. Journal of Shoulder and Elbow Surgery. 2005;14(4):385-392.
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Lewis J, Wright C, Green A. Subacromial Impingement Syndrome: The Effect of Changing Posture on Shoulder Range of Movement. Journal of Orthopaedic & Sports Physical Therapy. 2005;35(2):72-87.