Shoulder

The shoulder is considered a ball-and-socket joint, but the shoulder ball and socket is much different from that of the hip. The socket of the hip surrounds about 40% of the ball, but the shoulder socket surrounds only about half that. The top of the arm bone (humerus) forms the ball while an extension of your shoulder blade (scapula) called the glenoid forms the socket. The collarbone (clavicle) also forms a joint with a different extension of the scapula called the acromion and is called the acromioclavicular, or AC, joint. The scapula has multiple other projections including the coracoid and scapular spine which serve as attachment points for muscles and tendons that provide structural stability to the shoulder. Because the socket only surrounds such a small part of the ball, the shoulder is an inherently unstable joint, which is why the shoulder can frequently dislocate. This also means that several other structures are needed to provided stability to the shoulder, but still allow for high degrees of movement.

Several of the supporting structures and key aspects of the shoulder joint are listed below. Each of these structures has the potential to be injured and can lead to a pathology that may require treatment.

1. Articular cartilage is a very specialized tissue that lines the ends of the bones that form the joint and creates a smooth gliding surface. The cartilage is normally a few millimeters thick on each end of the bone. 
   • The cartilage can be damaged in a localized area or more diffusely. When the cartilage is damaged more diffusely, it is called arthritis.
     
2. The coracoacromial and coracoclavicular ligaments attach the undersurface of the clavicle to an extension of the scapula called the coracoid in order to stabilize the clavicle. The acromioclavicular ligament attaches the end of the collarbone to the adjacent acromion.
   • These ligaments can be damaged with AC separations.
3. The rotator cuff is a series of 4 muscles that attach the shoulder blade to the upper arm. These muscles are the subscapularis in front, supraspinatus on top, and infraspinatus and teres minor in the back. The muscles form tendons that coalesce to attach to the top of the humerus (upper arm bone). Each muscle has a separate function to elevate and rotate the arm, but act in concert. One of the main functions of the rotator cuff is to keep the humeral head centered on the socket.
   • One or more of these tendons can be torn. Rotator cuff tears are classified on a spectrum ranging from partial tears to full-thickness tears and are treated differently, depending on the size of the tear, how the tear occurred, and the activity level of the patient.
4. In the space between the acromion and rotator cuff, is a thin sac called the subacromial bursa. This sac provides lubrication, allowing the rotator cuff to glide under the acromion every time the arm is raised.
   • Inflammation can occur in this sac, causing it to swell. This is called bursitis. A bone spur on the undersurface of the acromion can also cause the bursa or underlying rotator cuff to get pinched in a condition called subacromial impingement. Both lead to pain when reaching above shoulder height, behind the back, or across the body.
5. The labrum is a thin piece of cartilage that attaches circumferentially around the glenoid (socket). It deepens the socket, allowing for more stability of the joint. It also acts as an attachment point for several ligaments and the biceps tendon.
   • The labrum can be torn in many different places. Often, labral tears are associated with shoulder instability.
6. The long head of the biceps tendon ascends up the humerus, curves over the top of the ball and attaches to the top portion of the labrum.
   • If the top portion of the labrum is torn, this may affect the biceps tendon function. This tendon can also become inflamed and cause shoulder pain.
7. The capsule is a thin connective tissue that surrounds the joint, providing some stabilization to the joint. It is normal for the capsule to be redundant or loose so that it can be stretched when the arm is moved into the extremes of motion.
   • Sometimes the capsule can become inflamed and tight like a drum, causing restricted range of motion and severe pain when the capsule is stretched. This is called adhesive capsulitis.
8. A synovial membrane lines the inner surface of the capsule and produces synovial fluid to lubricate the joint. It also provides nutrition to the cartilage.

Surgical

Initial Goals (1-6 weeks dependent upon surgical intervention):

• Pain reduction
• Reduce inflammation through Manual Therapy and Home Exercises
• Focus on restoration of passive range of motion initially with attention to the specific injury, particularly surgical versus conservative

Secondary/Progressed Goals (4-8 weeks):

• Restore full of range of motion – passive first, followed by active
• Prioritize the restoration of daily functional tasks
• Return to unweighted work duty function

Tertiary Goals (10-15 weeks):

• Initiate affected shoulder muscle recruitment and activation
• Restore strength through full range of motion
• Return to weighted work duty function

Return to Full Activity Level:

• Functional work testing
• Sport specific dynamic loading

Non-Surgical

Initial Goals (1-2 weeks dependent upon injury):

• Pain reduction
• Reduce inflammation through Manual Therapy and Home Exercises
• Focus on restoration of full range of motion with precautions for the specific injury, particularly surgical versus conservative

Secondary/Progressed Goals (3-6 weeks):

• Restore full range of motion – passive first, followed by active
• Prioritize the restoration of daily functional tasks
• Return to unweighted work duty function

Tertiary Goals (6-8+ weeks depending on the injury):

• Maximize affected shoulder muscle recruitment and activation
• Restore strength through full range of motion
• Return to weighted work duty function