Cambridge Shoulder - Subacromial impingement

Subacromial impingement

Subacromial impingement is very common.
The supraspinatus muscle and tendon run under the acromion and attach onto the greater tuberosity of the proximal humerus.
If you look at an X ray of the shoulder you will see "the ball" is not a perfect circle, the greater tuberosity works a little like an off set cam, in that if you rotate the arm upwards, the space under the acromion (subacromial space) reduces.
This space is not empty this is where the supraspinatus tendon runs.
The tendon then gets pinched (impingement) leading to pain.

I often describe sub acromial impingement in this slightly oversimplified manner, it is more than just a mechanical problem.
As the tendon ages the blood supply deteriorates, the ageing tendon degenerates and thickens (tendinopathy).
It is not a purely inflammatory condition although we talk about supraspinatus tendonitis it is often more a degenerative process of tendinosis.

Diagnosis
The diagnosis is made on a history of deep seated shoulder pain that may affect sleep.
The pain is often felt radiating down the side of the shoulder over the deltoid muscle and occasionally running down the front into biceps.
Pain right over the top of the shoulder is often coming from the acromiclavicular joint (ACJ).
Pain above and behind the shoulder in the region of trapezius is often related to the neck or muscular in relation to overuse of the parascapular muscles.

The pain is made worse with overhead activities and extending the shoulder behind your back, for example putting on a jacket or reaching into the foot well at the back of the car.
On examination full movement of the shoulder is possible but painful in the zone of impingement.
The zone of impingement or painful arc is where below shoulder height the shoulder is reasonably comfortable, when elevating the arm as it gets closer to shoulder height the pain increases being felt radiating into the deltoid.
Once the arm is above shoulder height the pain reduces slightly.
However when you lower the arm again, the pain returns at the level of shoulder height

Painful arc - The painful arc is this pain felt from around 60° elevation to 130°, particularly the pain improving slightly when you get above shoulder height.

Impingement testing, if you elevate your arm to 90° and then twist it, it increases the pain.
Sometimes there may be a little weakness of the shoulder related to pain or a tear in the rotator cuff (see rotator cuff tear).

X rays are requested to see if there is any signs of arthritis in the joint, to exclude any calcification in the tendon (see calcific tendonitis) and to look for bony abnormalities around the shoulder (see os acromionale).

An MRI scan or ultrasound sound scan may be requested to have a look at the soft tissues, particularly the rotator cuff to see if there is a tear in one of the tendons in the rotator cuff.
An MRI and or ultrasound is not always needed.

Treatment
Treatment is predominantly non operatively in the first instance. Around 80% of patients with acute onset of shoulder pain due to impingement or tendonitis will get better with non operative treatment within 6 months and not need any further intervention.
Surgery is only indicated if the symptoms don't resolve with 6 months of non operative treatment.

Non operative treatment
The main stay of non operative treatment involves
    Time/ Rest - relative rest
    Pain killers - particularly Non steroidal anti-inflammatories
    Physiotherapy
    Injections

Time/ Rest - Relative rest
Doing nothing is just as bad as doing too much, it is important to keep the shoulder moving so that it does not stiffen up and go onto a frozen shoulder.
Similarly continually hammering the shoulder and the tendons around the shoulder will perpetuate the impingement and swelling of the tendon.
Keep stretching the shoulder over shoulder height but avoid doing too much and avoid stressing the shoulder repeatedly particularly in the zone of impingement.

Pain killers
The best pain killers if you can tolerate them are the non steroidal anti-inflammatories (NSAIDS).
The pain killers are not only important in reducing the inflammation, but also preventing the pain spasm cycle. In response to pain all the muscles around the shoulder tighten up. The tense muscles then altering normal motion at the ball and socket joint and the shoulder blade.
Hence if the NSAID's are not controlling your pain it is important to add other pain killers to control the pain. (See pain killers).

Physiotherapy
Physiotherapy is important to keep range of motion in the shoulder and keep the muscles around the shoulder balanced and working together.
It is not about 5 or 10 minutes with a physiotherapist but getting into a regular rhythm of stretches and exercises every day.

Stretches to avoid posterior capsular tightness is important, so the ball can roll smoothly. Rehabilitating the 4 rotator cuff muscles is important so they can ensure smooth movement of the ball and keeping the humeral head (ball) well centred on the socket. It is not about just doing random exercises it is very important to balance the forces around the shoulder.

Injections
There are several different kinds of injections around the shoulder. Unfortunately none have been shown to be a miracle cure.
Steroid (cortisone) injections are very good for reducing inflammation and swelling but not very good for tendon healing.
In the past they were probably over used.
Now a days I would offer 1 maybe 2 injections but no more as repeated injections around the cuff can soften the tendon and lead to tendon rupture.
The injection should be around the tendon and not into the tendon.

Investigators are still looking for more effective injection treatments eg. platelet rich plasma.
There are several ways of injecting the shoulder from the front, the side and from the back.
I inject from the back minimising the risk of injecting into the tendon.
If the main problem is the biceps tendon then the injection is from the front under ultrasound guidance
Often the thought of the injection is worse than the reality.
A steroid injection often leads to a deep seated ache for 24 hours and then may take 4 to 6 weeks to reach full effect.

Operative treatment
Surgery is only indicated if non operative measures have failed.
Surgery involves a subacromial decompression - removing the spur on the under surface of the acromion and making more room in the subacromial space for the tendons.
A sub acromial decompression may be done open or arthroscopically.
At 6 months there is no difference in the final outcome, however in the short term arthroscopic or keyhole surgery is better tolerated.
An arthroscopic sub acromial decompression can be done as a day case or overnight stay.
On average the shoulder is improved by 60 to 80%, it is possible to shave away a little bone, but not take it all away as acromion is the anchor point for the deltoid - The power horse of the shoulder.

All surgery is associated with risk.
The risks generally being those of a general anaesthetic, infection risks <1:1000, stiffness, incomplete resolution, recurrence, frozen shoulder, nerve injury.

With keyhole surgery it is possible to see all of the shoulder and look for any rotator cuff tears or damage to the tendons and ligaments around the shoulder.
If damage is found to the rotator cuff it can often be dealt with at the same sitting arthroscopically (see rotator cuff tear)
In general range of motion returns at around 6 weeks, but it may take up to 3 months to feel the real benefits of pain relief. The shoulder will often continue to improve even a year to 18 months after the surgery.