Subacromial Impingement

There’s often not exclusively one reason for why a patient would develop subacromial impingent; rather, the condition is usually caused by a multitude of factors. We can group the causes of cuff inflammation into extrinsic degeneration (rotator cuff irritation from sources outside the tendon itself) versus intrinsic degeneration (the cuff tendon itself biologically degenerating). Some known risk factors for developing subacromial impingement include repetitive motions with the hand far from the body such as throwing, swimming, and lifting overhead which is common in some occupations. Weakness or an unbalanced strength coupling of the rotator cuff tendons can also lead to a poor position of the humeral head on the glenoid socket and lead to pinching of the front portion of the rotator cuff during these motions. Poor posture where the shoulders are rounded and the scapula (shoulder blade) sits more forward in a protracted position can cause the front rotator cuff to be pinched during activity. Additionally, if the bone above the rotator cuff called the acromion has bone spurs or has a more hooked shape, this can also narrow the subacromial space and cause pinching of the underlying rotator cuff tendons. Finally, age-related degenerative changes within the tendon itself can also lead to subacromial impingement.

The common symptoms of subacromial impingement include:

Pain

1. Patients usually point to the top or the outside of the shoulder and sometimes state that the pain radiates down the outside deltoid down to the lateral part of the upper arm.
2. Pain is exacerbated by reaching overhead, behind the back, or with heavy lifting.
3. Pain at night is classic for rotator cuff-related pain and we understand this as the rotator cuff is further pinched against the underside of the acromion. This can either be with laying on the affected shoulder at night or even when the patient tries to sleep on the other shoulder because the scapula sits in a protracted and forward position which is unfavorable for the rotator cuff. So night pain is very classic for rotator cuff problems and impingement.

Weakness

Because the cuff is being irritated, patients may notice weakness or fatigue with shoulder motion.

Clicking

Because the bursa that normally sits to help cushion the cuff from the overlying bone may get inflamed, this can lead to the patient feeling some clicking or catching or crepitation on the outside part of the shoulder due to irritation and thickening within the bursa

Subacromial impingement is first worked up on history and physical exam. Typically, patients have the classic symptoms of pain as described above in terms of presenting on the outside part of their shoulder, radiation up to but not past the elbow, worsened with lifting, and often present at night. Physical exam is essential because true subacromial impingement without tearing of the rotator cuff should not have weakness. On strength testing of the rotator cuff, the patient may have some pain but should not have any profound weakness. If there is weakness present on strength testing, then in addition to the impingement on the cuff, there may be a tear within the rotator cuff tendon, which represents a more severe condition. The typical tests that reproduce impingement for the shoulder include the Neer and Hawkins tests. These tests act to pinch the rotator cuff which will only be irritating to the patient if the cuff is already inflamed.

Imaging is important as x-rays are useful to look at the overall health of the glenohumeral joint to see if there’s any underlying cysts or bone spurs representing degenerative changes within the joint. They are also very useful to look at the amount of subacromial space present, the presence of bony changes at the cuff insertion on the greater tuberosity, and to note any bone spurs on the underside of the acromion. It is also important to examine any abnormalities in acromion morphology as we understand that more hooked or curved down-sloping acromions predispose patients to a higher risk of having impingement. MRI, Ultrasound, and CT are not required for the diagnosis of pure subacromial impingement, but as discussed before, if there are symptoms concerning for a rotator cuff tear, then an MRI should be pursued as this will help determine if there is a tear present and what the magnitude of that tear is.

The treatment options for subacromial impingement range from non-operative to surgical considerations.

Non-operative treatment protocol:

1. The goal of initial non-operative treatment is to decrease the inflammation of the shoulder
   • This is achieved with relative rest of the shoulder and avoiding painful overhead activity which would continue to irritate the rotator cuff. This may require the patient to have a short reduction or modification of their working conditions or a brief absence from playing certain overhead sports as shoulder inflammation calms down.
   • The use of ice for 20 minutes on the shoulder three times a day with a barrier between the ice and the skin can be helpful in calming inflammation in the shoulder
   • The judicious use of anti-inflammatory medications such as ibuprofen or meloxicam is also useful in reducing inflammation
2. Physical therapy is essential to help strengthen the rotator cuff and improve the scapula posture. As we’ve discussed before, abnormal scapular positioning is under-recognized as a persistent cause of cuff impingement. Stabilizing the scapula in its natural retracted position will help open up the subacromial space and prevent further pinching of the cuff.
3. Steroid injections into the subacromial space are an option to consider if other treatments are ineffective or if the patient would like a quicker reduction of the inflammation in the rotator cuff and the overlying subacromial bursa. Either with careful landmark guidance or under ultrasound, a needle is placed into the subacromial space above the rotator cuff tendons and a small amount of steroid can be injected here. The function of the steroid is to help reduce the inflammation overlying the cuff tendons and to help facilitate physical therapy in preventing the inflammation from returning. A steroid injection is not required for patients but is a thoughtful option to consider

Surgery

1. Surgery is fairly rare for just isolated subacromial impingement. Oftentimes, there are other conditions in the shoulder such as labral pathology or rotator cuff tears or biceps tears that are present at the same time as the impingement which necessitate surgical consideration.
2. It is essential to note that for pure subacromial impingement without associated problems in the shoulder, almost all patients are able to improve considerably without the need for surgery and are able to get back their function and have a relatively pain-free shoulder.
3. However, for truly refractory subacromial impingement that has failed an extended course of thoughtful non-operative management, arthroscopic surgery can be considered as a treatment option.
4. Surgery would be in the form of a subacromial decompression where we would smooth out any bone spurs that are pinching on the rotator cuff and help to create more space for the cuff tendons. We would also remove any overlying inflamed bursa. If there are any rotator cuff tears that are present with the camera in the shoulder at the time of surgery that were not apparent on a previous MRI, then these cuff tears can be appropriately addressed during surgery as well.

In orthopedics, prevention of disease is often much more valuable than curative measures. This means that if we can prevent a problem from occurring in the first place, that would be far preferable than needing injections or therapy or surgery after the fact to help correct the issue. In the context of subacromial impingement, how can we prevent this issue from either arising in the first place or coming back after it has been appropriately treated in the past? The ways we do this are to help maintain the proper health of the shoulder.

Ways to maintain shoulder health:

1. Regular rotator cuff and deltoid strengthening is essential to maintain the health of the shoulder. This can be taught by a professional physical therapist and continued at home as part of the patient’s daily home exercise program.
2. Strengthening the muscles around the shoulder blade (ex. rhomboids, levator, trapezius) and having the appropriate posture throughout the day is essential to help prevent re-pinching of the shoulder during motion. This is manifested as working on scapular protraction, retraction, abduction, adduction, and helping the shoulder fire as a coordinated unit. Additionally, posture shirts, which patients can often find online can help teach them how to keep their shoulder blades in a more ergonomic position throughout the day.
3. Proper warm-up before sporting activities or before prolonged repetitive overhead activities can also be very helpful in preparing the shoulder and helping to open up the subacromial space before embarking on these activities.
4. Activity modification is very helpful to prevent further pinching of the rotator cuff tendons after the initial inflammation has gone away. This means trying to avoid repetitive overhead strain on the shoulder when possible and modifying activities so the hands stay in front of the body and below the horizon of the shoulder as much as possible to reduce strain on the rotator cuff tendons.