The shoulder joint is a common site for injuries and pain due to its complexity and frequent use. Rotator cuff tears and shoulder impingement are common causes of shoulder discomfort. While both conditions can cause similar symptoms, they involve different underlying mechanisms and often require distinct management.
Understanding Rotator Cuff Tears
The rotator cuff is a group of four muscles and their tendons that surround the shoulder joint: the supraspinatus, infraspinatus, teres minor, and subscapularis. These muscles originate from the shoulder blade (scapula) and insert into the upper arm bone (humerus). They stabilize the humerus within the shallow shoulder socket, allowing for a wide range of motion, including lifting and rotating the arm.
A rotator cuff tear occurs when one or more of these tendons are damaged, ranging from fraying to a complete separation from the bone. Tears can result from an acute injury, such as falling on an outstretched arm or lifting a heavy object with a jerking motion. More often, tears develop gradually over time due to repetitive overhead activities, age-related wear and tear, or reduced blood supply to the tendons.
Understanding Shoulder Impingement
Shoulder impingement happens when the tendons of the rotator cuff and sometimes the bursa become pinched. This compression occurs in the narrow subacromial space, located between the top of the humerus and a bony projection of the shoulder blade called the acromion. When the arm is lifted overhead, this space naturally narrows, and inflamed or swollen tissues can get squeezed.
Common causes of shoulder impingement include repetitive overhead motions, which are often seen in athletes involved in sports like swimming, baseball, and tennis. Inflammation of the bursa (bursitis) or rotator cuff tendons (tendinitis) can also contribute to impingement by reducing the available space. In some individuals, the natural shape of the acromion or the development of bone spurs can narrow the subacromial space, making impingement more likely.
Distinguishing Symptoms
Rotator cuff tear pain is often a dull ache deep within the shoulder, which may radiate down the arm. Sharp pain can occur with specific movements, and a sudden “pop” or immediate weakness may indicate an acute tear.
In contrast, impingement pain frequently localizes to the front or side of the shoulder and often worsens with overhead movements, reaching behind the back, or sleeping on the affected side. This pain is typically a dull ache, though it can become sharp during certain arm positions. Both conditions can cause night pain, but it is often more disruptive and pronounced with impingement.
Weakness is a distinguishing factor. Rotator cuff tears often involve noticeable weakness, particularly when attempting to lift or rotate the arm. With impingement, a painful arc of motion (pain between 60-120 degrees of arm abduction) is common, and while there might be perceived weakness due to pain, true muscle weakness is less prevalent unless the impingement has led to a tear. Clicking or catching sensations in the shoulder are also more frequently associated with rotator cuff tears.
Professional Diagnosis and Next Steps
Accurate diagnosis requires a thorough medical evaluation, as self-diagnosis can be misleading due to overlapping symptoms. A healthcare provider will perform a physical examination, assessing the shoulder’s range of motion, strength, and performing specific tests to provoke pain or identify muscle deficits. These tests help to differentiate between various shoulder conditions.
Imaging studies are often used to confirm a diagnosis and rule out other issues. X-rays can reveal bone spurs or abnormal acromion shapes, which may contribute to impingement, and can also help exclude fractures or arthritis. Magnetic Resonance Imaging (MRI) is the most effective imaging for visualizing soft tissues like tendons and bursae, providing clear evidence of rotator cuff tears, inflammation, or fluid. An ultrasound may also be used to evaluate the rotator cuff tendons.
Seeking medical attention is important if shoulder pain is severe, persistent, worsens over time, or significantly interferes with daily activities. Initial self-care measures like rest and ice can provide temporary relief, but a professional diagnosis guides appropriate treatment.