Bone & Joint Expert Care

Click here to edit subtitle

Shoulder Anatomy

The shoulder is the most mobile joint in the body. The shoulder joint is similar to a ball-and-socket joint that is comprised of three main bones: the collarbone (clavicle), the shoulder blade (scapula) and the upper arm bone (humerus), which extends from the shoulder blade to the elbow. The upper end of the humerus where it rotates is a smooth, rounded head (ball) that fits into the glenoid cavity (socket) of the shoulder blade. Because the ball is larger than the socket, it is more flexible, but has less inherent stability.

Muscles, tendons and connective tissue protect the shoulder joint and hold the various parts together. Because the shoulder joint is stabilized by muscles and tendons, rather than by bone, the shoulder has great flexibility. This gives the shoulder joint a wide range of motion enabling movements such as lifting, pushing and pulling.

However, this great degree of motion has a trade off; the stability of the shoulder is dependent upon the surrounding soft tissue and can result in a larger number of problems not faced by other joints supported by bony structures. A healthy shoulder can be damaged by disease or injury, resulting in severe pain, pseudoparalysis (false paralysis) and muscle weakness.

Pain is one of the key reasons people consider joint replacement surgery. Intense pain can also limit your range of motion and prohibit you from performing your normal day-to-day activities or getting a good night’s rest. Your doctor may recommend non-surgical treatments initially; however, if conservative treatment has failed to provide you any relief, surgical options may be considered.

The shoulder is not a single joint, but a complex arrangement of bones, ligaments, muscles and tendons, providing strength and motion to the arm. The joint capsule, a watertight sac surrounding the joint, is formed by a group of ligaments that connect the humerus to the glenoid. The glenohumeral ligaments (GHL) provide the shoulder’s main source of stability, holding it in place and keeping it from dislocating. Collectively the supraspinatus, infraspinatus, teres minor and subscapularis muscles form the rotator cuff. The rotator cuff is a group of muscles which work together to provide the glenohumeral joint with dynamic stability, helping to control the joint during rotation.

The acromio-clavicular joint (ACJ) forms the junction between the collar bone (clavicle) and the top of the shoulder blade (acromium). The ACJ plays an important role in transmitting forces through the upper limb and shoulder to the axial skeleton (the body’s central axis). The ACJ has only minimal mobility though due to its supporting ligaments – the acromio-clavicular ligament and the coraco-clavicular ligament. The acromio-clavicular ligament restricts movement forwards and backwards. The coraco-clavicular ligament plays an important role in keeping the shoulder 'square'. They are extremely strong and support a heavy load.

 

Shoulder Anatomy

The Shoulder Anatomy begins with a little boney structure which includes: the shoulder blade, that's also known as the Scapula, the upper arm bone is the Humerus, and then the Collar Bone, which is also known as the Clavicle.

The Shoulder Blade is a relatively flat bone with a ridge that runs along the back side of itself, this is known as the Scapular Spine. At the end of that Scapular Spine is a curved piece, or bone, called the Acromion Process. The Acromion Process makes up a little tunnel inside above the ball and socket joint itself.

 

The Ball And Socket Joint

The Ball is a little bit bigger than the Socket of the joint, a lot of times we like to think of it as a basketball sitting on top of a golf tee. So to keep the ball aligned in such a shallow socket, we need a little tissue extension that makes that socket just a little bit deeper. And that little extension is called the Glenoid Labrum. The Glenoid Labrum is sort of like cartilage, but not really cartilage. That can be a bit of a problem sometimes inside the joint when someone has a dislocated shoulder or an unstable shoulder.

The shoulder is the most flexible joint in the human body. It is also one of the most complex, with a greater range of motion than any other joint. It enables us to raise, bend, rotate and swing our arms. A properly functioning shoulder is not only critical to the golf game, but to many activities of daily living.

The shoulder is our most mobile, yet least stable joint. Its tremendous range of motion makes the shoulder less stable, and it is generally more prone to injury and dislocation than our other joints.

The shoulder is made up of three bones: the upper arm bone (humerus), the shoulder blade (scapula) and the collarbone (clavicle).

These bones are joined together by muscles, ligaments and tendons that support and stabilize the shoulder, allowing the arm to function.

The shoulder is composed of four joints:

  • The glenohumeral joint is the main joint of the shoulder. It is where the rounded top part of the arm bone, the humeral head or "ball", meets the "socket" (glenoid) of the shoulder blade. This joint is referred to as a "ball and socket" joint in terms of its shape and function. The joint surfaces interact in a manner similar to a golf ball on a tee. The socket is very shallow and smaller than the ball, therefore the joint is inherently less stable than a true ball and deep socket, such as the hip joint.

 

  • The sternoclavicular joint is the joint between the sternum (chest bone) and collar bones.

 

  • The acromioclavicular joint, commonly called the AC joint, is where the collarbone meets the highest point of the shoulder blade (acromion).

 

  • The scapulothoracic joint is between the rib cage and the shoulder blade

Several important ligaments can be found in the shoulder joints. The primary function of the ligaments is to provide stability to the inherently unstable joint and to strengthen the capsule that surrounds the shoulder.

Many muscles are responsible for movement in the shoulder, but the primary muscle groups are the rotator cuff, the deltoid and the trapezius.

The rotator cuff is a group of muscles and their tendons that attach our upper arm to our shoulder blade. The most important job of the rotator cuff muscles is to provide stability for the ball (the end of the upper arm bone) in the socket and specifically center the ball within the socket during functional movements. The rotator cuff is also responsible for lifting the arm out to the side, as well as external and internal rotation of the shoulder.

 

The deltoid muscle group is responsible for shoulder flexion (raising our arm straight out in front), abduction (raising our arm directly out to the side), and extending our arm behind our back.

The trapezius is a large kite-shaped group of muscles extending from the low back to the neck. These muscles, known as "traps", are divided into an upper, middle and lower portion and work along with other muscles on the joints of the shoulder. The upper traps elevate the shoulder (shrug), the middle traps retract the shoulder (shoulder blade squeeze) and the lower traps depress the shoulder (shoulder blade pushed downward).

 

Normal Range of Motion

The normal range of motion of the shoulder can vary. A golfer who lacks normal range of motion may be at greater risk of shoulder injuries. The average golfer should have normal range of motion of the shoulder in three directions:

 

  • Golfers should be able to comfortably raise their arms overhead

 

  • They should be able to reach directly behind their back and touch the space between their shoulder blades with their thumbs

 

  • They should be able to place their hands behind their head and open both elbows equally out to the side.

 

What is the Rotator Cuff?

The muscles that surround the shoulder are known as the Rotator Cuff Muscles. And Sometimes you hear people talking about their Rotator Cup, but it's not really a cup it's more like a cuff on your wrist or shirt sleeve. It's made up of four muscles: Supraspinatus, Infraspinatus, Teres Minor, Subscapularis. Those four muscles are what make up the Rotator Cuff. The Rotator Cuff is a group of very small muscles, that are a little bit thicker than a lasagna noodle, maybe a little bit wider, if not just as wide and certainly not as long. So they are very small muscles.

At the end of each muscle there is a tendon. The tendon will connect the bone to the muscle belly itself. So in order to do that, we get a tendon at the end of each of these muscles. This is where we tend to get a lot of these Rotator Cuff breakdowns and some other conditions.