What is it?
Impingement of the shoulder, as the name implies, refers to a pinching of the soft tissues between the arm bone or ball of the shoulder and the bone that forms the roof of the shoulder. It is characterized by pain along the outer upper arm that worsens with overhead activities such as throwing, serving or lifting. Patients often complain of weakness with an aching pain that frequently will wake them at night. The rotator cuff area consists of four muscles that surround the upper and outer portions of the ball of the shoulder (humeral head). Their function is to push down on the shoulder and bicep tendon, and stabilize the shoulder joint so when the larger muscle groups fire (i.e. the deltoid) the arm is raised and the bones do not scrape against each other. However, any time tendons cross a joint, there is risk of friction and abrasion. In order to protect against that friction, the body creates fluid filled sacs called bursae, that surround and protect the areas. The bursa of the shoulder sits over the top of the rotator cuff and allows for improved gliding of the cuff tendons between the shoulder bones with shoulder motion. Yet, if this bursa becomes inflamed suddenly due to an injury or traumatic event; or if it is chronically irritated from a dysfunctional rotator cuff, bony prominences, improper lifting, throwing or job mechanics, the space provided for these soft tissues becomes compromised and increased swelling and pain occur. This is most commonly referred to as subacromial bursitis with rotator cuff tendonitis.
Historically, the teaching was that impingement was the result of differently shaped bony roofs (acromions) of the shoulder, some with less space for the soft tissues. These different shapes were classified as Type I, II and III with Type III having the least amount of available space (see figure). Patients with shoulder symptoms will frequently ask, “Is that bony spur or differently shaped acromion, the cause of all of my problems?” The answer is that it depends on their history and mechanism of injury. Sudden traumatic injuries when there is a Type III acromion can lead to impingement simply because the cuff tendons become pinched and respond with inflammation and scarring. On the other hand simply having a Type III acromion does not mean that you are going to develop pinching and pain. The opposite is true, where a person has lived their entire life without symptoms but have used their shoulder excessively for work and play. As the rotator cuff becomes degenerative, its ability to keep the ball (humeral head) depressed and in the socket, lessens. The result is a rotator cuff and bursa that can now be pinched by the bony roof above. If the bony roof is flat, the pinching will be evenly distributed with less pain. If the roof is spiked or hooked, impingement symptoms are more likely to be present.
Am I at risk?
Impingement is common in athletes of all ages and in middle-aged people based upon the activities being performed. Young athletes involved in contact sports such as football, wresting and weightlifting are at an increased risk. Additionally those athletes who use their arms overhead for swimming, baseball, and tennis are particularly vulnerable. Laborers who do repetitive lifting or overhead activities using the arm, such as paper hanging, construction, or painting are also susceptible. Pain may also develop as the result of minor trauma or spontaneously with no apparent cause.
Preventative measures are often neglected by laborers and athletes. These measures include an appropriate warm up and stretch before work, practice or competition. Above all the use of proper technique may be the single most important factor when it comes to prevention.
Initial treatment consists of nonsteroidal anti-inflammatory medications and ice to relieve the pain. Physical therapy is typically prescribed focusing on stretching and strengthening exercises, and modification of the activity that caused the problem. If there is concern that a rotator cuff tear may also be present an MRI scan will usually be ordered. Injections of steroid and numbing medication may be ordered as long as a rotator cuff tear is not present. These injections reduce inflammation which can ultimately lead to long-term pain relief. Care must be taken with activities immediately following an injection because they weaken muscle and tendon, making them more vulnerable to injury.
When nonsurgical treatment does not relieve the pain or disability the Orthopaedic Surgeon may recommend surgery. The goal of surgery is to remove any bony projections or scarred bursa as well as address any other existing pathology (rotator cuff dysfunction) that may be contributing to the formation of impingement.
Recent studies have shown that by taking a minimalist approach to conserve the acromion, results in greater patient satisfaction and fewer complications. Different techniques are in use at this time but the overall goal remains the same; to decompress the subacromial space by removing the inflamed bursa and release the ligament while removing the acromial curve, hook, or bone spur. Arthroscopic techniques utilize a small camera and instruments that are inserted via small incisions, into the shoulder joint. This allows for other issues to be addressed at the same time, while maximizing what the surgeon can see in that space. Thermal engergy in addition to a motorized shaver is used to remove the bursa followed by a high-speed burr for bony removal.
Post-rehabilitation and exercises are an important part in achieving a successful surgical outcome. The ultimate goals are to decrease or eliminate the pain and to regain motion and strength so that a return to sport or activities of daily living can be initiated. The Orthopaedic surgeon will provide a rehabilitation program based on the patient’s needs and the findings at surgery. This will include exercises to regain range of motion of the shoulder and strength of the arm. Complete recovery typically can be expected between 6-8 weeks after surgery.
The Bottom Line:
Anything that decreases the available space for the soft tissues (rotator cuff and bursa) so that they then become irritated and inflamed can lead to impingement or worsen it if already present. When attempting to diagnose impingement, all potential causes and risk factors are taken into consideration to determine the best treatment for the patient.