The Shoulder joint is one of the most flexible joints in the human body compared to other joints. The shoulder joint is a ball and socket between the scapula and the humerus. It is the primary connection that connects the upper limb to the trunk.
The shoulder joint is different from other joints in the body. Its structure allows more movement than others. For free movement, the ball is much larger than the socket, often compared to a golf tee-ball. It means the shoulder is more dependent on the soft tissue around it that helps to place the joint and control its movements.
This shoulder flexibility provides an extensive range of motion at the upper end 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.
These various movements also make the shoulder unstable. This instability is offset by muscles, tendons, ligaments, and rotator cuff glenoid labrum. They work together so you can quickly move the shoulder. As you learn more about the shoulder and joint sections, you can better understand your shoulder anatomy.
This article provided by Dr B. Chandra Sekhar discusses the Types of the shoulder joint and its functions.
A flexible joint called the ball, and socket joints formed by humerus and scapula. This joint gets lined with cartilage that covers the face of the glenoid socket and the humeral head. The joint stabilize by a fibrous cartilage ring (labrum) around the glenoid socket.
Ligaments connect the shoulder bones, and tendons attach these bones to the muscles around them. The biceps tendon muscle attaches to the shoulder, which helps to stabilize the joint. Four short muscles that originate from the scapula extend around the shoulder where their tendons joined into the rotator cuff.
When you think of the shoulder layer, the innermost layer is bone, then the joint capsule and ligaments, followed by tendons and muscles on the surface. Nerves and blood vessels supply the muscles and bones of the shoulder. Nerves convey signals from the brain to the muscles to move the shoulder and direct messages from the muscles back to the mind to relieve pain, pressure, and temperature. Here are the details of the different shoulder Joints:
The shoulder is one of the most complex and huge joints in the body. The shoulder joint formed where the humerus (upper arm bone) fits like a ball into the scapula joint (shoulder blade). Other important bones in the shoulder are:
In general, there are four main joints related to complex shoulder, including the collarbone, shoulder blades, ribs, sternum, and humerus, this all work together to provide all movements for the upper parts in all three planes of motion.
The action moves into the shoulder joint complex of each of these four joints. The interaction of the four joints they are:
- Glenohumeral joint
- Acromioclavicular joint
- Sternoclavicular joint
- Scapulothoracic joint
The movements involved in each joint are continuous, even though they occur at different speeds and various stages of arm lifting.
Glenohumeral Joint and Its Function:
Glenohumeral Joints (GH Joints) are right synovial diarthrodial joints with the ball and socket, which are responsible for the connection of the upper part of the body trunk. This joint formed by an attachment of humeral head and the glenoid fossa of the scapula. Remember that the glenoid fossa is flat, while the humerus bone is a large and round hemisphere. This bone conformation, combined with a highly mobile scapula, allows for full movement in all three planes but does not increase high-level stability.
It is interesting to note that the GH joint ligaments and capsules are relatively thin and only provide secondary stability to the joints, while the main stabilizing power of this joint can maintain by the surrounding muscles, especially the rotator cuff muscles. This joint is the most flexible and unstable in the body as it is the most commonly dislocated joint in the body.
Function: The ball and socket GH joint is a combination that allows 3 degrees of freedom. The main movements of this joint connection are internal and external rotation, flexion and extension, and abduction, adduction but also horizontal abduction and adduction.
Acromioclavicular Joint and Function:
An acromioclavicular (AC joint) joint is a gliding, or plane style synovial joint formed by the connection of the lateral clavicle and the scapula acromion process. It helps in attachment of the scapula to the collarbone. It functions as the connection that suspends the upper body to the trunk. In essence, this joint connects the movement of the scapula to the lateral end of the clavicle.
Function: The AC connection allows movement in all three fields: up and down rotation, horizontal plane rotation (internal and external rotation), and sagittal plane rotation (anterior and posterior). This relatively mild but significant adjustment movement helps perfect the movement between the scapula and the humerus. This movement allows contact between the scapula and posterior thorax, which is essential.
Sternoclavicular Joint and Function:
The sternoclavicular joint (SC joint) forms by the articulation of the medial aspect of the clavicle and the sternum manubrium. This joint is the only direct attachment of bone to the upper body to the axial skeleton, and the connection must be stable at the same time while allowing high mobility.
It has a fibrous articular disc with a thin and robust ligament tissue, which often results in a collarbone fracture before the SC joint gets dislocated. SC joint structure is a saddle joint with concave and convex surfaces at each articular joint surfaces. This joint allows the collarbone to move in all three planes.
Function: Movements include elevation and depression, protraction and retraction, and axial rotation.
Scapulothoracic Joint And Function:
Although this is a scapulothoracic joint, the articulation between the scapula and the thorax is not a right connection because it does not have the characteristics of fibrous, cartilage or synovial joints. It is an articulation of the anterior aspect of the scapula in the posterior thorax.
Usually refers to the movement of the scapula towards the posterior rib. SC joints and AC joints are interdependent with this joint because the scapula attaches through acromion process to the lateral end of the collarbone and through the AC joint the clavicle, in turn, attaches to the axial skeleton of the chest manubrium through the SC joint. Thus, any movement of the scapula in thorax will cause movement of either Ac or SC joints or both. For normal shoulder function, a healthy shoulder and Scapulothoracic Joint posture is essential.
Function: Movements in the Scapulothoracic Joint include protraction and retraction, elevation and depression, and up and down rotation.
Let us see other structures that are present in the joint:
If two or more bones meet than it is known as joint. Most joints are flexible, allowing bones to move. The connection consists of the following components:
- Cartilage: This is a type of tissue that covers the bone surface in a joint. Cartilage reduces friction in the joint motion.
- Synovial membrane: A network called the synovial membrane connects the joint and seals it in a joint capsule. The synovial membrane releases sticky fluid (synovial fluid) around the joint to lubricate it.
- Ligaments: Ligaments surround the joint to support and limit joint movement. Ligaments bind bones together.
- Tendon: Tendons (another type of rigid connective tissue) on each side of the joint are attached to the muscles that control the movement of joints. Tendons connect muscles to bones.
- Bursa: Liquid-filled sacs are called bursae between bones, ligaments, or other nearby structures. They reduce friction in the joints.
- Synovial fluid: A Clear and sticky fluid secreted by the synovial membrane called Synovial fluid
- Meniscus: This is the curved section of cartilage in the knee and other joints.
Shoulder joints are an extraordinary combination of healthy bones, flexible ligaments and tendons, and healthy cartilage and muscles. It’s very flexible and allows lots of motions in a wide range. However, this complex structure also tends to wear out quickly, causing arthritis pain and possible injury to one of the structures.
If you are interested in knowing how the shoulder joints work, and if you are the one who is suffering from any of the shoulder related problems and looking for the best treatment, visit Dr B. ChandraSekhar. Contact 9959588389 and book your appointment now!