A separated shoulder, or acromioclavicular joint injury, is sometimes referred to as a shoulder sprain.

The AC joint is the area where the acromion—the bony projection at the top of the shoulder blade—meets the clavicle, or collarbone. In this injury, the ligaments that support and stabilize the shoulder are stretched or torn, and the bones of the AC joint become dislocated or separated.  Common causes of a shoulder sprain include trauma directly to the shoulder—from a car accident, for example—as well as a fall onto an outstretched arm.

Shoulder sprains are separated into grades, depending on the extent of damage to the ligaments and the degree of separation between the clavicle and the acromion.

• Grade 1 sprain: the ligaments of the AC joint stretch or partially tear, but the bones don’t separate. Mild pain and swelling may interfere with normal daily activities, such as putting on a coat.
• Grade 2 sprain: ligaments tear, causing pain and swelling.
• Grade 3 sprain: the AC joint becomes completely separated. Tears in the AC ligament and the nearby coracoclavicular ligaments, which connect the shoulder blade to the clavicle, cause the collarbone to dislocate. This leads to bruising, pain, and swelling that can prevent you from performing your usual activities. The dislocated collarbone usually appears as a bump on the shoulder.
• Grades 4, 5, and 6: these sprains are more severe and less common. In these injuries, ligaments tear, the AC joint separates, and muscles detach from the collarbone.

A shoulder strain is a stretching or tearing of a muscle or tendon in the shoulder. It can happen when the shoulder remains in one position for long periods of time, such as when carrying a heavy backpack over one shoulder or having poor posture while typing. Playing sports that require repeated overhead movements of the arms, such as swimming or tennis, also increases a person’s susceptibility to shoulder strain.

A shoulder tear is an injury to the soft tissues that give the joint range of motion and stability. A tear can occur in the tendons, the muscles, or the labrum, a rim of fibrous tissue that lines the glenoid.

A tear may be partial or it may sever a tendon, muscle, or the labrum completely. Over time, small tears in a tendon can lead to a bigger tear.  Shoulder tears can be caused by repeated use or by sudden injury. Years of repetitive arm motions performed during sports, chores, or jobs can lead to a tear. Athletes who play sports that require repetitive motions, such as baseball, tennis, and weightlifting, may experience a shoulder tear. A tear can also occur if you break a fall with an outstretched arm.

A dislocated shoulder occurs when the humerus becomes dislodged from the glenoid, which can pull muscles and tendons out of place and cause them to tear. Bony growths in the joint called bone spurs can rub against tendons, causing friction that may lead to a tear.

Symptoms include pain, a decrease in range of motion, and instability, which can feel like your shoulder may shift out of place. You may not notice a very small tear, whereas a complete tear can cause persistent, aching pain accompanied by weakness or even paralysis in the affected arm. However, symptoms are not always predictable. A small tear can be very painful, and a large tear may cause no symptoms.

Rotator Cuff Tear

A rotator cuff tear occurs in any of the muscles and tendons that connect the upper arm to the scapula, or shoulder blade. Four rotator cuff muscles help your shoulder to rotate. Four tendons work with the muscles to stabilize the shoulder and allow you to lift and move your arm in many directions.

Biceps Tendon Tear

A biceps tendon tear occurs in the tendon that attaches the biceps muscle to bone. The biceps muscle runs along the humerus and helps the arm to bend at the elbow and rotate from side to side.

Two biceps tendons attach this muscle to the shoulder. The short head tendon connects the biceps muscle to the coracoid process, a bony projection at the top of the shoulder blade. The long head tendon connects the muscle to the top of the glenoid labrum, or shoulder joint socket. A tear in the long head tendon is fairly common, but short head tendon tears are rare. This is because the position of the long head tendon in the biceps makes it vulnerable to injury.

Labral Tear

A tear in the labrum, the fibrous tissue that lines the shoulder socket, may occur. The head of the humerus is wider than the socket, and the labrum deepens the socket, helping it fit better, which stabilizes the joint. Several ligaments attach to this area of the shoulder. Injuries here can result from a single trauma or repetitive use of the shoulder.

If this tear affects the top half of the socket, where the biceps tendon connects to the shoulder, it is called a SLAP (superior labrum anterior and posterior) tear. In this injury, the biceps tendon may also tear. If a labral tear occurs on the bottom half of the socket, at the front of the shoulder, it is called a Bankart tear. If it affects the back of the shoulder, it is called a reverse Bankart tear.

If you have a labral tear, you may notice a slight clicking or popping noise when you move your arm. You may also feel a catching sensation in the joint, as though it can’t move any farther. These occur when a piece of the labrum gets stuck between the bones of the joint.