SHOULDER DISLOCATION

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related talks: shoulder instability; broken shoulder (proximal humerus fracture); separated shoulder (AC joint); broken arm (humeral shaft fracture); rotator cuff tear

What is a Shoulder Dislocation?

A shoulder dislocation is when the arm bone (humerus) separates from the shoulder blade bone (scapula) after a traumatic injury.

Our shoulder is a ball and socket joint where the arm bone (humerus) is the ball that fits into the glenoid (a part of the shoulder blade, "scapula"). The shoulder has an incredible range of motion (move your shoulder around and you see its more flexible than any other joint), which is great for activities, but there is always a trade-off. In the shoulder, as you increase flexibility (increased range of motion) you are sacrificing stability - The shoulder dislocates 10x more commonly than all other joints combined.

The shoulder looks like a golf ball sitting on a tee (and think about how easy it is for a golf ball to fall off the tee). Therefore, because the bone architecture is so unstable, the body tries to compensate using the surrounding muscles (like your rotator cuff) and the surrounding soft tissue (like the labrum, and ligaments) to provide additional stability.

When the shoulder dislocates, some of these stabilizers will be injured. In people under 40 years old, the inferior ligament and labrum and joint capsule complex is commonly torn. In people over 40 years old, the rotator cuff is typically torn. This is a general guideline but injury patterns are certainly more variable in real life.

Sometimes the ligament-labrum complex will actually tear off a chip of bone from the joint socket (glenoid rim), and this is called a "Bony Bankart Lesion". Sometimes, when the dislocation is very severe, the humeral head gets whacked against the joint socked and causes an indentation, almost like when you press too hard on a ping-pong ball. This is called a "Hill Sachs Lesion". This creates an abnormally shaped "ball" which can easily dislocate from the "socket".

Shoulder dislocations occur in people of all ages and they can be caused in many ways. It most commonly occurs as someone is falling and they grab for something to break their fall. In this position the arm gets forced in a position of abduction (movement away from their body) and external rotation, which causes the arm bone to come forward out of the joint (anteriorly direction). About 95% of shoulders dislocate anteriorly (forward). Posterior dislocations are very rare (the and and are mainly seen in people having seizures, getting electrocuted, or if you are a baseball pitcher with chronic laxity of your posterior joint capsule from the stress of pitching.

How is a Shoulder Dislocation diagnosed?

A shoulder dislocation can often be seen by the well trained eye. The affected shoulder will lack the normal shape, and it will appear to sag downward. Because the joint is out of place, people will be complaining of significant pain and inability to move the shoulder. Diagnose is confirmed with a series of 3 x-rays (an AP view which is front to back, a lateral view which is from the side, and an Axillary view which looks through the armpit). The axillary view gives the best view of the joint, but the other views are also very helpful and can also identify other injuries like a fracture (which can occur at the same time).

How is a Shoulder Dislocation treated?

Once the x-rays confirm the shoulder is out (dislocated), its important to put it back in place. This prevents severe muscle spasms, worsening pain, further injury to the ligaments, and also kinking of blood vessels and nerves. All the nerves, arteries, ligaments, and muscles are at the perfect tension and length when the bones are in their normal position. When the bones fall out of place, everything is being stretched or bent, and thats why theres so much pain with a dislocation. Most people report the pain almost disappears once the shoulder is put into place.

To re-locate the shoulder, doctors typically inject lidocaine into the shoulder joint (the same type of medicine that dentists use to numb a tooth), and give morphine (for pain relief) and give a muscle relaxant (to decrease muscle spasms that will prevent efforts to put the shoulder back in place). In general the shoulder wants to return to its natural position, and so it shouldnt require too much force to re-locate the shoulder.

The shoulder is relocated using a "Milch procedure", where the arm starts at the person's side and is slowly raised over their head (almost like combing your hair), while pressure is placed at the humeral head (inside the arm pit). This works in the majority of cases. If thats unsuccessful, then a traction-countertraction technique is used (this is a technical term for a pretty "non-technical" approach where one person pulls on the arm, while the other pulls on the body, in a position where the arm is aligned to fall back into the socket).

Once the shoulder is in place the arm is protected in a sling, and the person should be reminded to keep the arm near the body (the opposite position of what causes the dislocation). Oftentimes people will experience numbness over their shoulder, and this can occur in up to 50% of cases, and its due to a temporary axillary nerve injury (from being stretched). Expect this numbness to resolve (its almost like a stinger seen in football).

Further treatment, like physical therapy or surgery, depends on the other associated injuries. As previously mentioned, rotator cuff tears (see talk) or a labral tears (see talk) are common and require treatment.

What is the long term outcome?

If you are under 20 years old, theres about an 85% chance you will dislocate your shoulder again. If you are 20-25 years old the risk is still 50-75%. This occurs because the shoulder is de-stabilized by soft tissue injury. Many people in this age group will elect (its not required) to have their labrum repaired to prevent further dislocation (see talk).

People older than 40 years old have a low risk of repeat dislocation, but a higher risk of rotator cuff injury (about 15% at 40 years and up to 40% at 60 years and up). Its generally recommended to get early repair of the rotator cuff following dislocation (see talk).