• Hardayal Singh, MD

Shoulder - A Unique & Complex Joint

Our shoulder joint is quite an interesting joint as it is very unique and complex in its anatomy. Since the shoulder is the most mobile joint in our body, it needs a high degree of flexibility, but it also needs to remain stable in multiple planes of motion. To accomplish this, the shoulder joint is supported by a combination of bones, ligaments, and muscles.


4 Shoulder Joints

The shoulder - just by default people think it is just one joint, but really what it is a conglomerate of the ball and socket also known as (1) glenohumeral joint that everybody agrees is a shoulder joint, but there is a one more joint above it.


We call that the (2) acromioclavicular joint and there is a joint behind it, which is the (3) scapulothoracic and even the joint that connects to the neck are called the (4) sternoclavicular joint that goes with the clavicle and all these 4 joints (believe it or not) make the shoulder and we have our expertise of the whole 4 joints, but mainly the ball and socket joint of the upper extremity is what we call the shoulder joint more often.

  1. Glenohumeral Joint

  2. Acromioclavicular Joint

  3. Scapulothoracic Joint

  4. Sternoclavicular Joint

Shoulder Anatomy | Carolina Regional Orthopaedics

Ball and Socket Joint

Unlike a hip joint which is to some degree more of a ball being encased by the bone, this is something the size of a golf ball sitting in a teaspoon, but it helps in place by ligaments that come from the scapula and a ligament is a fibrous tissue that goes from bone-to-bone and encapsulates this and seals it together.

Ball and Socket Joints | Carolina Regional Orthopaedics

There is actually another lining in there that secretes a lubricating fluid, but the overhead throwing athlete or the lacrosse player or the athletic who just falls on an outstretched arm can tear the ligaments that hold these 2 bones together, that is separate and distinct from damage to the actual cartilage, which we will talk about in a little bit.


As you get older damage can occur to the actual cartilage.

There is a Teflon like coating. God gave us a slippery coating on the ends of our bones that touches another bone and that is called cartilage.


Functions of Shoulder Joint

The primary function of the shoulder girdle is to give strength and range of motion to the arm such as flexion, extension, abduction, adduction, internal and external rotation, and 360° circumference in the sagittal plane.


Besides, the arm allows protraction retraction, raising and depression in the scapula.

This cartilage makes the shoulder joint stable by creating more space in the glenoid or the shallow shoulder joint. It supports a variety of movements like swinging of the arm and rotation.


The rotator cuff plays a major role in the internal and external rotation, flexion and abduction of the upper arm in the shoulder joint. These muscles work as a team because they are responsible for making your shoulder joint stable. Each rotator cuff muscle performs a specific and important function for your shoulder joint.


Shoulder Muscles

  1. Supraspinatus – aids in abduction (lifting arm up to the side)

  2. Infraspinatus – main contributor of shoulder external rotation (rotating arm outwards)

  3. Subscapularis – main contributor of shoulder internal rotation (rotating arm inwards)

  4. Teres minor – assists infraspinatus in external rotation and extension (carrying arm backwards)

Importance of Shoulder

We use our shoulders from the second we wake and even during our sleep. Shoulder movement is important for performing activities of daily living (ADLs), including household chores, preparing meals, recreational activities, brushing your hair, dressing, turning in bed and closing doors.


Also, shaking hands, caring for your children, reaching into cupboards, lifting various objects. Shoulder dysfunction can cause reduced mobility leading to decreased functional independence and a decreased quality of life.


Takeaway

Shoulder joint is the most mobile part in our body. Many do not understand the importance of shoulder joint. A simple fall can injure your shoulder and affect your activities of daily living and I strongly encourage you to take care of your shoulders. I hope the above information was made you see your shoulder in a new light. I will see you in my next article.


Carolina Regional Orthopaedics

Carolina Regional Orthopaedics provides the most effective, modern, and innovative techniques in both Orthopedic Surgery and Pain Management using proven methodologies in both the surgical and non-surgical treatment of all conditions affecting the spine, upper extremities, and lower extremities. We specialize in hand and wrist surgery, joint replacements, sports medicine, trauma care, pediatric orthopedics, pain management, wound care, regenerative medicine, physical therapy, imaging services, and EMG testing.

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