Shoulder impingement syndrome is one of the most commonly seen shoulder injuries. It usually manifests as pain or a pinching sensation in the shoulder joint during specific motions. The pain can significantly affect both strength and range of motion which limits the arms functional ability. SIS can manifest by itself, or in conjunction with other rotator cuff issues and soft tissue irritation.
To better understand shoulder impingement, there’s some essential anatomy of the shoulder to cover. First off is the rotator cuff itself.
The rotator cuff is composed of four deep muscles which all attached to the head of the humerus arm bone in your shoulder joint. These muscles are the supraspinatus, infraspinatus, teres minor, an subscapularis. The tendons of these muscles wrap around the humoral head to form a “cuff”. This cuff helps to stabilize the humoral head in the socket, known as the glenoid fossa, during movement.
While these muscles produce many of the motions are shoulder joint is capable of, they are not necessarily strong muscles. Larger and more superficial muscles like the lats an deltoid produce power with these motions, while the deep rotator cuff muscles stabilize the joint.
This ball and socket joint, known as the glenohumeral joint, is one of the most mobile joints in the body. This allows us to perform a wide variety of functional movement, but also makes this joint inherently less stable compared to other joints.
In addition to the glenohumeral joint, the shoulder also has another joint known as the acromioclavicular joint. This joint is formed by the acromion, a spine coming off the shoulder blade, and the clavicle (collarbone). You can palpate this joint by walking your finger down your collarbone to a pointy bump just above the deltoid.
The supraspinatus muscle which forms AB duction parentheses think of a snow Angel motion, runs underneath this acromioclavicular joint. A fluid filled sac, known as a bursa, sits between these structures and reduces friction and compression on the supraspinatus muscle during this motion as the head of the humerus glides upwards.
With inflammation, the soft tissue structures like muscles and tendons become puffy and larger while the joint space remains the same. This causes a mechanical lack of space, and can compress on muscles during shoulder movement, causing pain. The supraspinatus in particular is susceptible to this impingement and causes the majority of shoulder impingement symptoms.
Along with the pain, patients often experience decreased strength and range of motion as well. All these combined can severely limit the functional ability of that arm. Neck issues often accompany shoulder impingement syndrome as the other muscles begin to compensate for the rotator cuff. Difficulty sleeping due to pain can further exacerbate pain and other symptoms. If left untreated it can quickly lead to other issues and injuries.
With treatment it is possible to reduce the inflammation and irritation in the affected structures. Physical therapy can restore both range of motion and proper mechanical function of the shoulder. Injections into the joint space can further help manage pain and inflammation which allow you to better tolerate PT. Catching the symptoms early before they can progress further is vital for restoring shoulder function and reducing pain levels. Shoulder impingement syndrome responds well to consecutive treatment, an should be exhausted before considering surgical intervention.