Shoulder and Humerus

The shoulder is the portion of the body that joins the arm to the chest and back.  It is the most mobile joint in the body.  It helps control the arm in space.  This allows us to reach overhead, in front of us, and even, to a smaller degree, behind us. 

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Shoulder Anatomy:

The humerus, or upper arm bone, connects to the chest/back at a “cup” of bone known as the glenoid.  The scapula, or shoulder blade sits behind the glenoid and the collarbone comes over the top.  Basically , where all these bones come together (along with the muscles around it) form the shoulder. The shoulder joint is a ball-and-socket type-joint that was designed more for mobility rather than stability.  It is very similar to a golf ball on a tee with a large ball relative to a small scoket.  The ball (humeral head) is maintained in the socket (glenoid) during overhead motion by various soft tissue stabilizers.

 Many people are familiar with a group of muscles known as the rotator cuff.  These are 4 smaller muscles surrounding the shoulder.  They help stabilize the shoulder in activities such as throwing.

  • The first soft tissue stabilizer is called the labrum. The labrum is a thin rim of cartilage that is attached to the outer edge of the glenoid. This fence-like labrum provides depth to the glenoid, helping to maintain the humeral head in the center of the socket.

  • The second stabilizer is the shoulder capsule. The capsule is a thin sheet of connective tissue that envelops the humeral head and attaches to the entire glenoid rim, similar to covering a ball on a tee with plastic wrap. There are 4 major thickenings in the capsule known as the glenohumeral ligaments. These glenohumeral ligaments are very important in stabilizing the humeral head and keeping it centered on the glenoid during overhead motions.

  • The third stabilizer is a group of muscles that include the rotator cuff, biceps and scapular stabilizers.These muscle groups,termed dynamic stabilizers, not only move the shoulder through elevation and rotation, but also help the labrum and capsule stabilize the ball in the center of the socket.  These dynamic stabilizers also keep the shoulder blade (scapula) moving smoothly during overhead motions. In other words,when the shoulder rotates forward very rapidly (about 2000 degrees of arc per second as in throwing a ball overhead), the dynamic stabilizer muscles contract not just to accelerate the ball, but also to help keep the ball from sliding off the socket which would result in a shoulder dislocation.

 

ACUTE INJURIES

AC joint injuries: 

The AC joint has two key groups of ligaments that help support it.  The AC ligament runs side to side and a pair of Coracoclavicular(CC) ligaments help stablize the joint from top to bottom.  It can be injured by direct blows to the shoulder or after a fall on the shoulder.

An xray will usually show the collarbone being displaced, or moved from it’s normal position.  Most cases of AC joint injuries do not need surgery.  However, the more severe ones may need surgery.  Your doctor can discuss the severity of your injury with you and why he/she recommends to operate or not.  

Proximal Humeral Physeal Fractures:

Injuries to the growth plate of the humerus can occur after using the arm too much or after a traumatic event.  Because of the ability for this part of the body to remodel, or grow, the prognosis for these is often excellent with nonoperative treatment.  Breaks can occur through, above, below, or both above and below the growth plate.  In cases where the fracture has been displaced severely, your surgeon may recommend surgery using pin, plates and screws, or a rod that goes into the arm bone to stabilize the break until it heals. 

Humeral shaft fractures:

Breaks in the middle of the upper arm bone are often due to trauma.  This includes car accidents, falls, or other types of injuries.  One thing to be aware of when there is an arm bone fracture is the risk of injury to one of the nerves that makes its way down the arm.  Your doctor will perform a thorough physical exam during the initial evaluation and throughout the course of your treatment to determine whether or not this is present. Like many of the injuries we’ve already discussed, oftentimes these breaks do not need surgery and can be treated with immobilization.  Initially, the arm is placed into a splint and a sling.  Typically 1-2 weeks later, once the initial swelling has subsided, most children will be transitioned into a Sarmiento brace.

 In the radiographs above, the first one on the left demonstrates a break in the middle of the humerus bone.  This patient already has a splint in place.  Two weeks later, the patient was placed in the sarmiento brace.  Notice how there is some new bone forming on both sides of the fracture.  This new bone is known as fracture callus.  Lastly- the xray on the right shows the humerus healed.  Note how the bone will "correct itself" in terms of its position.  Especially in children, not every bone has to be lined up perfectly in order to heal perfectly.

 

OVERUSE INJURIES