How Do Rotator Cuff Injuries Occur?

The shoulder’s complex anatomy allows for strength and tremendous flexibility. This complexity also makes the shoulder prone to injury, and rotator cuff injuries are common.

See Guide to Shoulder Anatomy

Rotator cuff injuries are typically attributed to trauma, tissue degeneration, and shoulder impingement. Baseball pitchers have a distinctive throwing motion that puts them at a higher risk for rotator cuff problems. All four of these sources of injury are explained below.

See Soft Tissues of the Shoulder

1. An acute injury is caused by single traumatic event

A rotator cuff can be injured in a single trauma, such as trying to break a fall with an arm outstretched, lifting a heavy weight, or activities that place a tremendous amount of force or strain on the shoulder, such as holding a waterskiing tether.

2. Degeneration occurs over months or years

As people age and/or overuse their shoulders over time, the rotator cuff degenerates—especially in people over 40 and those in occupations that require frequent raising and lowering of the arm, such as roofing or carpentry. Tiny tears develop in the rotator cuff, making it weaker and more prone to larger tears. It is possible for these larger tears to occur without any notable trauma.

3. Shoulder impingement causes the rotator cuff to be pinched or squeezed

Rotator cuff degeneration is sometimes associated with impingement. Shoulder impingement syndrome is an umbrella term that describes the painful pinching of muscles, tendons or other soft tissue that is sandwiched in between the bottom of the scapula’s acromion and the top of the shoulder’s ball-and-socket joint (glenohumeral joint). This space is called the subacromial space.

See Shoulder Pain: Is it Shoulder Impingement?

Shoulder impingement can be caused by:

Structural issues. The rotator cuff may be compressed when the space between the acromion and humerus is inherently too small. This occurs with:

• A hooked or curved acromion
• Thickening of ligaments under the acromion
• Degenerative changes of the acromioclavicular joint

A physician may refer to any one of these problems as a bony limitation of the acromion.

See Causes and Risk Factors of Shoulder Impingement

Functional issues. While the rotator cuff muscles keep the shoulder’s ball-and-socket joint stable, other muscles, including the deltoid, pectoralis, latissimus, and trapezius, provide the shoulder with most of its power. As the rotator cuff fatigues, a person can have power without adequate stability.

Rotator cuff fatigue or bad biomechanics (e.g. bad form during heavy lifting) can set into motion a series of events in the shoulder, as follows:

• Mal-tracking occurs between the shoulder joint’s humerus head (ball) and glenoid (socket). Mal-tracking refers to when a joint’s bones do not align normally or move against each other smoothly.
• Mal-trackings put more strain and pressure on the rotator cuff muscles.
• Strain and pressure on the muscles can cause pain as well as additional weakness and instability.

A physician may refer to these events as a superior translation of the humerus that compresses the rotator cuff and bursa. When tension and pressure exist in the small subacromial space, soft tissue can become inflamed and damaged.

A rotator cuff injury can cause inflammation that leads to shoulder impingement or, conversely, shoulder impingement can lead to a rotator cuff injury. For example, bone spurs resulting from osteoarthritis can cause the rotator cuff to be pinched, damaging it over time.

See What Is a Bone Spur?

4. Repetitive throwing motions

It is not uncommon for baseball pitchers to have rotator cuff injuries. Baseball pitchers can experience the problems described above, but their specialized throwing motions can create distinct paths to rotator cuff injury, as follows:

• In the late cocking/early acceleration phase, immediately prior to throwing a ball, a pitcher’s arm is lifted away from the body and externally rotated. This motion can cause compression of the rotator cuff as well as the labrum, a ring of tough cartilage that fits in the shoulder socket.
• During the deceleration phase, immediately after the ball’s release, the shoulder experiences distraction forces that can lead to tensile strength failure of the rotator cuff.
• SICK (Scapular malposition, inferior medial border prominence, coracoid pain, and dyskinesis of scapula) is associated with shoulder injuries, including rotator cuff injuries. SICK, sometimes called SICK scapula syndrome, is defined by several factors, including poor position and mechanics of the scapula, and a tight inferior glenohumeral ligament. ¹ Economopoulos KJ, Brockmeier SF. Rotator cuff tears in overhead athletes. Clinics in sports medicine 2012 October 1; 31-4:675-692 Overhead throwing athletes are more prone to SICK.

An elite pitcher with shoulder pain may want to seek medical advice from a physician experienced in treating similar athletes.

Whether shoulder rotator cuff injury is caused by trauma, shoulder impingement, or elite athletic participation, the condition can be the source of pain, stiffness, and other symptoms.

See Diagnosing Shoulder Impingement