A “separated shoulder” is the common term for an injury affecting the acromioclavicular (AC) joint, which is distinct from a dislocated shoulder. A dislocated shoulder involves the main ball-and-socket joint, but a separation occurs higher up. This injury involves the ligaments connecting the collarbone (clavicle) to the shoulder blade (scapula) at the top of the shoulder. Severity ranges from a mild sprain to a complete tear of the supporting structures.
The Joint Involved and How Injury Occurs
The acromioclavicular joint is located where the outer end of the clavicle meets the acromion, a bony projection from the shoulder blade. Two primary sets of ligaments stabilize this joint. The acromioclavicular ligaments surround the joint capsule. The stronger coracoclavicular (CC) ligaments anchor the clavicle to the coracoid process, a different part of the scapula. These ligaments keep the clavicle aligned with the acromion.
The most frequent cause of an AC joint separation is a direct, forceful blow to the top of the shoulder, often seen in contact sports like football or rugby. This impact drives the shoulder blade downward while the clavicle remains in place. The injury can also result from a fall onto an outstretched hand (FOOSH) or a fall directly onto the shoulder. When the force is strong enough, the ligaments stretch or tear, allowing the clavicle to move out of its normal position relative to the acromion.
Identifying the Visual and Physical Symptoms
The visual sign of a separated shoulder is often a noticeable “bump” or prominence where the collarbone meets the shoulder blade. This deformity occurs because torn stabilizing ligaments allow the weight of the arm to pull the shoulder complex down, leaving the end of the collarbone elevated beneath the skin. The size of this bump generally correlates with the severity of the ligament damage.
Physical symptoms begin with sudden and intense pain localized directly at the AC joint immediately following the injury. This pain is accompanied by swelling and tenderness in the area, making it painful to press on the top of the shoulder. Bruising may also develop around the joint shortly after the trauma.
Moving the arm, especially lifting it overhead or across the body, significantly increases pain due to stress on the damaged joint. Patients often hold the injured arm close to the body for comfort, a position known as an arm-supported gait. The shoulder may feel weak or unstable. In more severe cases, a grinding or clicking sensation may be felt when attempting to move the arm.
Understanding the Severity of Separation
AC joint separations are classified using a grading system based on the extent of damage to the AC and CC ligaments and the resulting displacement of the clavicle. Grade I represents the mildest form, involving a simple sprain or stretching of the AC ligaments without significant tear or joint displacement.
A Grade II separation involves a complete tear of the AC ligaments, but only a partial tear or sprain of the stronger CC ligaments. This results in some noticeable, though often slight, upward displacement of the clavicle. Grade III is a more severe injury involving a complete tear of both the AC and CC ligaments, leading to significant and obvious upward displacement of the clavicle and a large bump on the shoulder.
Less common, higher-grade separations (Grades IV, V, and VI) involve greater displacement or movement of the clavicle in different directions, such as pushing backward or under the coracoid process. These types involve extensive ligament and surrounding soft tissue damage.
When to Seek Medical Attention
For a suspected AC joint separation, initial care should follow the RICE protocol: Rest, Ice, Compression, and Elevation. Immobilizing the arm in a sling helps rest the joint and provides immediate comfort. Applying ice to the top of the shoulder for 15 to 20 minutes several times a day minimizes swelling and pain.
It is important to seek prompt medical attention after any fall or impact that causes significant shoulder pain or limited movement. You should see a healthcare professional immediately if you observe a severe deformity or a large, prominent bump on the top of the shoulder. Urgent medical evaluation is also required for severe pain, a complete inability to move the arm, or any signs of nerve or circulation issues, such as numbness, tingling, or coldness in the arm or fingers.