Condition
Shoulder impingement
Shoulder impingement is the pinching of the rotator cuff tendons and the subacromial bursa between the humeral head and the bony arch above the shoulder (acromion). It is the most common cause of shoulder pain, particularly with overhead activity.
Anatomy
The subacromial space
The acromion is a bony arch that sits above the humeral head. The space between the acromion and the humeral head is called the subacromial space, and it contains the rotator cuff tendons and the subacromial bursa, which is a thin, fluid-filled sac that lets the cuff glide smoothly under the bone.
When the arm is lifted, the rotator cuff and bursa pass through this space. Anything that narrows the space, or anything that makes the cuff or bursa thicker, can cause them to be pinched during movement.
Pathology
How impingement happens
Impingement is a final common pathway for several different underlying problems. Recognising the underlying cause matters because the right treatment depends on it.
- Bony anatomy. Some patients have a hooked or down-sloping acromion, which narrows the subacromial space and predisposes them to impingement.
- Bursitis. Inflammation of the subacromial bursa thickens the bursa and fills the space.
- Rotator cuff weakness or dysfunction. A weak cuff cannot keep the humeral head centred on the glenoid, so the head rides upward and pinches against the acromion.
- Cuff tear. Tears, particularly partial-thickness tears, can cause the cuff to swell and impinge.
- Calcific tendonitis. Calcium deposits within the cuff cause swelling and severe pain.
- Scapular dyskinesis. Poor control of the shoulder blade during movement can change the way the acromion moves over the cuff and cause impingement.
Symptoms
How impingement feels
The classic symptom is pain in the shoulder that comes on with overhead activity. Patients often describe pain on reaching into a high cupboard, hanging out the washing, or doing push-ups, gym pressing, or swimming.
A painful arc is common: pain through the middle range of arm elevation, with relative comfort below and above that arc. Pain at night is also common, particularly when sleeping on the affected side.
Weakness and crepitus may also be present, particularly when impingement is associated with a rotator cuff tear or significant bursitis.
Diagnosis
How impingement is diagnosed
Clinical examination is usually enough to confirm impingement, with positive impingement signs and a painful arc. Imaging is used to identify the underlying cause and to look for associated pathology.
- X-rays. Show the bony anatomy, the shape of the acromion, and any calcific deposits within the rotator cuff.
- Ultrasound or MRI. Used to assess the rotator cuff and bursa. MRI is more accurate, particularly for surgical planning.
- Subacromial injection test. A diagnostic injection of local anaesthetic into the subacromial space. If the pain settles immediately, that confirms the subacromial space as the source of the pain. This is often done when the diagnosis is not clear, and is usually combined with a cortisone injection so one injection is both diagnostic and therapeutic.
Treatment
Treatment options for impingement
Most cases of impingement settle with non-operative treatment. The aim is to reduce inflammation in the subacromial space, then re-balance the rotator cuff and scapular control so the cuff passes cleanly under the acromion. Surgery is reserved for cases that have not responded to a thorough course of conservative treatment, or have a large, hook-shaped spur on the acromion.
- Activity modification. Temporarily reducing the overhead activities that flare the pain.
- Anti-inflammatory medication. A short course of an oral anti-inflammatory if appropriate.
- Physiotherapy. The mainstay of treatment. Targeted rotator cuff and scapular-control exercises retrain the shoulder mechanics so the cuff is no longer being impinged.
- Subacromial corticosteroid injection. Reduces inflammation in the bursa and breaks the pain cycle. Most effective when used to allow physiotherapy to progress.
- Arthroscopic subacromial decompression. Keyhole surgery to remove the inflamed bursa and trim the undersurface of the acromion to widen the subacromial space. Reserved for cases that have not responded to non-operative treatment, or where the structural anatomy is the dominant problem.
When impingement is associated with a significant rotator cuff tear, the cuff tear itself becomes the focus of treatment. See the rotator cuff tear page for more on those situations.
Recovery
Recovery from treatment
Most patients with impingement improve over six to twelve weeks of physiotherapy, sometimes supported by a corticosteroid injection. A meaningful improvement in pain and function should be evident over that period; if it is not, the diagnosis is re-checked and surgical options are considered.
Recovery from arthroscopic subacromial decompression is relatively quick. A sling is worn for comfort for a few days only. Active movement starts straight away, with strengthening from around four to six weeks. Most patients return to office work within a week or two and to manual or overhead work over several weeks.
FAQ
Frequently asked questions
- What causes shoulder impingement?
- Impingement is the pinching of the rotator cuff tendons and bursa under the bony arch above the shoulder. Common underlying causes include the shape of the acromion (a hooked or down-sloping acromion narrows the space), bursitis, rotator cuff weakness or tear, calcific tendonitis, and poor scapular control during movement.
- Will shoulder impingement go away on its own?
- Most cases do, with a course of physiotherapy and activity modification. Targeted rotator cuff and scapular control exercises retrain the shoulder mechanics so the cuff is no longer being impinged. A short course of anti-inflammatories or a corticosteroid injection can break the pain cycle and allow physiotherapy to progress.
- How is impingement diagnosed?
- Impingement is mostly a clinical diagnosis, based on history of pain with overhead activity, a positive impingement sign on examination, and a painful arc through the middle range of arm elevation. Imaging (x-rays, ultrasound, or MRI) is used to identify the underlying cause and look for associated cuff tears or calcific deposits.
- When is surgery for impingement needed?
- Surgery is reserved for cases that have not responded to a thorough course of non-operative treatment over six months and where the structural anatomy (e.g., a hooked acromion) is the dominant problem. Arthroscopic subacromial decompression involves trimming the undersurface of the acromion and removing the inflamed bursa.
- Is impingement the same as a rotator cuff tear?
- No. Impingement is the mechanical pinching of the cuff and bursa under the acromion, which can cause pain even without a tear. A rotator cuff tear is detachment of the tendon from the bone. The two conditions often coexist, but impingement can occur with an intact cuff and many cuff tears do not present with classical impingement signs.
Pain with overhead activity?
Book an appointment with Dr Piper
Consultations at Lakeview Private Hospital, Norwest. Bring a referral and any imaging you have.