Shoulder Impingement

Shoulder impingement is the painful catching that occurs in the space between the head of the humerus and the shoulder blade arch (acromion). The pain occurs with elevation of the arm to shoulder height. The pain is felt down the outer aspect of the upper arm or into the biceps muscle region. The pain is often worse at night and interferes with sleeping.

Structures that occupy the subacromial space (blackened area) include:

1. The rotator cuff tendons. The rotator cuff muscle (supraspinatus) helps lift your arm up. The muscle sits on top of the shoulder blade and its tendon (yellow) runs through the subacromial space to connect to the head of the humerus
2. A fluid filled sac, called bursa (orange) lubricates the motion between the rotator cuff tendons and the acromion
3. The coraco-acromial ligament attaches onto the under-surface of the acromion

Causes of impingement include

1. Thickening of the contents of the subacromial space.

1. The subacromial bursa in response to repetitive trauma can become thickened, inflamed and painful
2. The rotator cuff tendons with repetitive overload or aging can form degenerate thickened areas of scar (tendinosis). If the rotator cuff tears the retracted portion of the tendon thickens and the torn edge may catch on the boundaries of the tunnel. Rarely calcium deposits can form in the tendon (see calcific tendinitis
3. The coraco-acromial ligament attachment may thicken or turn into a bony spur
   
   

2. Variations or changes in the bony margins can narrow the acromial space: different acromial shapes, bony spurring from the acromion or an arthritic AC joint and rarely an unstable piece of acromial bone (os-acromiale).

3. Dynamic factors: by avoiding the painful areas of above shoulder activity and reaching behind your back, secondary problems of rotator cuff weakness and stiffness occur that increase impingement.

Investigations of shoulder impingement include:

1. X-rays: can show acromial shape, acromial and AC joint spurs
2. Ultrasound: can show bursal thickening, rotator cuff degeneration or tearing and assess impingement with arm motion
3. MRI: is generally reserved for resistant cases of impingement where surgical treatment is being considered. It enables assessment of both bone and soft tissues
   

The treatment of shoulder impingement depends on the cause, duration of symptoms and disability and previous treatments.

The non-operative treatment involves:

1. Activity modification: activities that increase the pain and make sleep more difficult should be avoided in the acute inflamed stage and gradually reintroduced
2. Pain management: options include simple painkillers, anti-inflammatories and steroid injections into the subacromial bursa
3. Physiotherapy: can assist with restoring range of motion and rotator cuff strength. Progression to a swimming or gym-based exercise program completes the rehabilitation
   

Surgical treatment of impingement is reserved for patients with:

1. Greater than 6 months of pain and disability that is interfering with quality of life
2. Surgical targets (eg. acromial spurs) and evidence of impingement (thickened subacromial bursa) on MRI
   
   

The surgery involves increasing the size of the subacromial space for the rotator cuff tendons, by removing thickened bursa and abnormal bone. The surgery takes about 1 hour, requires an anaesthetic and can be performed as a day or overnight stay. A sling is worn for comfort only. Shoulder range of motion exercises are commenced the next day and a formal strength program begins around 4 weeks after surgery.

The surgery provides a relief of pain in 80-90% of patients. Operations specific risks include but are not limited to infection, skin nerve injury, shoulder stiffness and incomplete relief of pain.