The Science of Shoulder Impingement Syndrome
Shoulder impingement (subacromial pain syndrome) involves irritation of the rotator cuff tendons and bursa in the subacromial space. Despite the name, it's now understood as more than just mechanical compression. The tendons develop degenerative changes and the bursa becomes thickened, not from simple pinching but from a complex interaction of factors. Modern understanding shifts away from blaming the shape of your acromion (the 'hooked' acromion seen on X-rays is common in pain-free shoulders too). Instead, we focus on functional problems: how your shoulder blade moves, rotator cuff strength, and posture all play crucial roles. Shoulder impingement frequently coexists with rotator cuff injuries, as both conditions share similar underlying biomechanical issues. In some cases, untreated impingement may contribute to the development of shoulder bursitis, and chronic impingement can lead to compensatory patterns that contribute to frozen shoulder.
Contributing Factors
Most shoulder impingement is 'secondary' or functional, meaning it's caused by movement problems rather than bone shape. Key contributors include weak or fatigued rotator cuff muscles, imbalanced scapular stabilizers (typically tight upper traps and pectoralis minor with weak serratus anterior and lower traps), and posterior capsule tightness.
In overhead athletes, the kinetic chain matters enormously. Any weakness from the legs and core forces the shoulder to overwork. Poor hip stability or core strength means your shoulder compensates to generate power, leading to fatigue and eventual breakdown. This is why I assess your whole body, not just your shoulder.
Common aggravating factors include the 'boom-bust' cycle of overdoing on good days, specific movements like overhead reaching or reaching behind, sleeping on the affected shoulder, and periods of increased stress which heighten muscle tension and pain sensitivity.