What Is Shoulder Impingement?

What is it?
Shoulder impingement or sub acromion pain syndrome is a complex condition with many contributing factors. It is characterised as pain from compression of the structures within the sub acromial space (between the scapula arch and the head of the arm). Impingement has symptoms of pain when lifting the arm by the side, out in front, reaching, lifting objects, and when sleeping on the effected arm. Patients often complain of pain in the shoulder of a gradual onset or following a period of excessive upper limb activity. Symptoms are felt either in the front or back of the shoulder and can refer down the upper arm. A common sign is the painful arc, whereby lifting your arm by your side causes pain between 40 and 120 degrees as the sub acromial space narrows.

Types and contributing factors
There are 2 main types of impingement; Sub acromial and Internal impingement.
Sub acromial can be either primary or secondary impingement. Primary is due to structural narrowing within the sub acromial space due to either a tear or degeneration of the rotator cuff muscles, including calcified tendinopathy, AC joint osteoarthritis, acromial bone spurring, and humeral head osseous remodelling.
Secondary impingement is due to functional narrowing of the structures between the acromion and the humeral head. This is mainly caused by poor shoulder joint mechanics due to poor scapular positioning and control, lack of humeral head control within the shoulder cavity, poor posture, stiffness of the shoulder capsule, and rotator cuff weakness or overuse leading to tendinopathy. The common structures effected with secondary impingement include the: rotator cuff tendons, sub acromial bursa, Long head biceps tendon, and the superior glenoid ligament.
Internal impingement is caused by compression of the underside fibres of certain rotator cuff muscles between the humerus and the shoulder capsule, not the acromion, with certain movements. This is also due to faulty shoulder mechanics and typically presents as anterior or posterior shoulder pain during throwing motions.

Secondary impingement causes:
– Poor scapular movement and control. Commonly include elevated, anteriorly tilted, downwardly rotated, medial and inferior border winging. Muscle tightness and weakness contribute to this.
– Shoulder laxity/instability creating excessive movement within the capsule/joint.
– Poor posture. Excessive upper back curvature with rounded shoulders.
– Muscle tightness. Commonly of the pectorals, latissimus dorsi, and lower neck muscles, which can pull the scapula and arm into sub-optimal positions.
– Muscle weakness. Commonly the scapula upward rotators and depressors; lower and middle trapezius, serratus anterior, and muscles of the rotator cuff.
– Tendon damage / microtrauma. Due to sudden or chronic overuse creating swelling of the tendons. Poor scapula mechanics and joint laxity can strain the tendons as they have to work harder than normal to keep the ball of the arm in the socket.

How Can Physiotherapy help?
Physiotherapy can identify specifically what is causing your shoulder pain and impingement, through a detailed physical assessment. Following this, your muscular and joint imbalances can be addressed through using soft tissue techniques, joint mobilisations, taping, dry needling and proprioceptive training. Depending on what is causing your symptoms, an individualised muscle activation, strengthening, and stretching program can be prescribed. If left unresolved shoulder pain can become worse with chronic damage to the rotator cuff tendons and bursa, possibly leading to a primary impingement and tearing of the tendons.