Shoulder impingement occurs when the rotator cuff tendons and the subacromial bursae are compressed as they pass through the subacromial space formed between the acromium, the AC joint and the head of the humorous (arm). Impingement causes irritation to the tendons and bursa leading to inflammation of the bursa, damage to the tendons and possible tearing of the rotator cuff.
There are two types of shoulder impingement; primary and secondary.
Primary shoulder impingement occurs when the superior structures of the shoulder encroach the subacromial space. This occurs with a misshapen acromium where the acromium develops a hook or a curve on the end of it. Other causes of primary impingement include thickening of the corocoacromial arch or spurs formed over the AC joint. As you elevate your arm the tendons in your rotator cuff will be compressed against these spurs causing the impingement leading to aggravation or degeneration. These abnormalities tend to develop in the over 35 age group and will generally get worse over time.
Secondary impingement is the aggravation of the rotator cuff against the superior shoulder structures, this time however it is caused through muscular imbalances/weakness/poor control rather than bony deformities.
Secondary shoulder impingement may be caused through weakness of the rotator cuff or a relative over recruitment of the supraspinatus muscle in the rotator cuff. The supraspinatus functions like the rest of the rotator cuff to stabilise the shoulder by compressing the head of the humorous (arm) into the shoulder socket during movements. The difference between the supraspinatus and the other rotator cuff muscles is the attachment point of the muscles. Where the other rotator cuff muscles work from the sides as a force couple to compress the shoulder, the supraspinatus attaches from above. When the supraspinatus and the deltoids become stronger than the surrounding rotator cuff stabilisers it can cause an upward glide of the humorous. This upward glide of the humorous causes encroachment of the subacromial space and causes secondary impingement. Secondary impingement can also be caused by other dysfunctions such as other muscular imbalances or tightness causing positional shifts in the shoulder joint. An example of this would be in swimmers or in gym participants with overdeveloped pectorials and latissmus dorsi muscles which will cause the shoulder to roll forward. This position change will cause the shoulders anterior structures to become aggravated, the subacromial space to be narrowed and more place stress on the rotator cuff muscles as they will now be working in a lengthened position.
The stabiliser of the shoulder blade also play an important role in the functioning of the shoulder. They provide the role of stabilising the shoulder blade holding it in the correct position and giving it a good base to work from. Muscles such as the serratus anterior are very important as it holds the shoulder blade close to the rib cage. This is a muscle typically weak in the majority of patients especially those post surgery or suffering from shoulder impingement.
Impingement can lead to a whole lot of other conditions including:
- Subacromial bursitis
- Biceps tendinopathy
- Calcific tendinopathy
- Rotator cuff tendinopathy
- Rotator cuff tears
- Glenoid labrum injuries
Symptoms of shoulder impingement include:
- Pain on the outside, front, back or top or your shoulder.
- A painful arc of abduction, this refers to pain when you hold your arm straight out to the side that decreases as you move higher or lower.
- Discomfort at full shoulder movements.
- Pain on the lateral side of the shoulder joint.
- Tightness of the shoulder muscles.
- Restricted shoulder movement, difficulty reaching up behind your back.
- Pain on lifting or throwing.
The only way to treat the spurs associated with primary shoulder impingement is by removing them through surgery, normally an acromioplasty. Physiotherapy will still help in primary impingement by reducing the inflammation and restoring proper movement. Often secondary impingement will occur concurrently with primary shoulder impingement.
Treatment should be considered as a two part process. The first part is to reduce the inflammation and pain in the shoulder and to regain full movement. The second part consists of correcting the biomechanical errors that led to the development of this condition in the first place. Generally this will involve a biomechanical or technique analysis to check for any deficiencies.
These biomechanical deficiencies include:
- Poor postural alignment.
- A hypomobile (stiff) thoracic or cervical spine.
- Faulty movement patterns of the shoulder.
- Muscle tightness restricting the shoulder movement.
- Shoulder capsular restrictions.
- Weakness of the rotator cuff.
- Weakness through the scapular stabilisers.
- Weakness of the core stabilisers causing altered shoulder function.
Treatment needs to be progressed carefully otherwise more shoulder pain may develop. Commonly patients with impingement will try physiotherapy or other forms of treatment and have limited success. What we find is that an incorrect diagnosis was made and the treatments weren’t specific enough for the condition. Quite often the patient will be encouraged to do too much strengthening exercises before the muscular tightness or capsular restrictions have been addressed. As with all injuries it is important to address the entire functioning body because for example; if the shoulder impingement was actually being caused by a stiff thoracic spine no amount of massage or rotator cuff strengthening will fix your impingement problems. Strengthening is vitally important to ensure the correct shoulder stabilisation is occurring through all your movements however the key is to integrate these into your rehab at the correct time to ensure optimal recovery.