Thursday, February 26, 2015
STERNOCLAVICULAR JOINT
The sternoclavicular joint is truly an amazing structure of our body. It allows us to move our shoulder backward and forward. It is supported by different ligaments and protected by an outer layer. The inner layer secretes synovial fluid that allows smooth movement.
Functionally, the joint behaves as a ball and socket system. The fulcrum for most movement is the costoclavicular ligament.
It is innervated by the medial supraclavicular nerve and the nerve to subclavius.
The SC joint connects your clavicle (collarbone) to your sternum, which is the large bone down the middle of your chest. This attachment is the only bony joint linking the bones of the arm and shoulder to the main part of the skeleton.
Like most joints, the SC joint is made up of two bones covered with a material called articular cartilage. Articular cartilage is a white, smooth material that covers the ends of bones in a joint. Articular cartilage allows the bones of a joint to rub together without much friction.
Only a small section of the SC joint actually connects to the sternum. This makes the bony connection somewhat unstable. However, extra ligaments cross the SC joint to give it more stability. Ligaments attach bones to other bones.
It seems like this construction would make SC joint dislocation common, but a dislocation is actually very rare. The ligaments surrounding the SC joint are extremely strong. These ligaments are very effective at preventing dislocations. Four different types of ligaments hold the joint in place.
The intra-articular disc ligament attaches to the first rib and divides the joint into two separate spaces. This ligament is very thick and fibrous.
The costoclavicular ligament is short and strong. It attaches underneath the clavicle to the first rib just below. It helps steady the SC joint during certain motions.
The interclavicular ligament supports the ends of both clavicle bones near the SC joint. It passes over the top of the sternum, connecting one clavicle to the other.
The capsular ligament reinforces the capsule that surrounds the SC joint. This ligament keeps the sternum end of the clavicle from pointing up as the other end of the clavicle drops down.
A part of the clavicle called the physis does not turn into bone until you are about 25 years old. The physis is a section of cartilage near the end of the clavicle. Bone growth occurs at a physis, which is also called a growth plate. Between age 20 and 25, the cartilage physis fuses into bone. Injuries to the physis in people under 25 may look like an SC joint dislocation. But sometimes the injury is actually a fracture through the growth plate.
General Characteristics of the STERNOCLAVICULAR JOINT
Almost all joints allow movements in certain degrees while others do not allow any movement. The sternoclavicular joint enables the clavicle and shoulder to move in a great extent. There are two layers of a SC joint; the outer and inner layer. The outer layer, also known as the stratum fibrosum, is composed of avascular white fibrous tissue. The outer layer is abundant with nerve endings and nerve roots. The inner layer, also known as the stratum synoviale, is made up of fluid. It is crucial in reducing friction between the two joining bones. Because of the synovial fluid, the clavicle could slide smoothly and painlessly over the manubrium.
Movements of STERNOCLAVICULAR JOINT
The sternoclavicular joint allows movement of the clavicle in three planes, predominantly in the anteroposterior & vertical planes, although some rotation also occurs. Muscles dont directly act on this joint, although almost all actions of the shoulder girdle or the scapula will cause some motion at this articulation.
The unique double-hinged articular disk found at the junction of the clavicular head and manubrium allows for movement between the clavicle and the disk during elevation and depression of the scapula. This disk also allows motion between the sternum (manubrium) and itself during protraction and retraction of the scapula.
Sterno-Clavicular joint MRI anatomy & Protocols CLICK HERE
Sternoclavicular joint injuries
Usually only through significant force do the ligaments supporting the sternoclavicular joint become completely disrupted, enabling dislocation of the joint. The extent of the damage to the supporting ligaments and capsule dictates whether the joint subluxes or dislocates. Sternoclavicular joint injuries are graded into three categories.
First degree injury: a simple sprain, which involves an incomplete tear or stretching of the sternoclavicular and costoclavicular ligaments. This is the most common type of sternoclavicular joint injury.
Second degree injury: the clavicle subluxes either anteriorly or posteriorly from its manubrial attachment, causing a complete breach of the sternoclavicular ligament but at most, only a partial tear of the costoclavicular ligament
Third degree injury: a complete rupture of the sternoclavicular and costoclavicular ligaments, permitting a complete dislocation of the clavicle from the manubrium.
A significant force (direct or indirect) to the shoulder can cause a traumatic dislocation of the sternoclavicular joint.
anterior dislocations of the joint are much more common (by a 9:1 ratio) usually resulting from an indirect action, such as a blow to the anterior shoulder that rotates the shoulder backwards thereby transmitting the stress to the sternoclavicular joint.
posterior dislocations of the joint are usually a result of a force driving the shoulder forwards, or from a direct impact to the superior sternal or medial clavicular surfaces. An example of the latter would be falling on a rugby ball with your team mates landing on top of you!
Sternoclavicular joint arthritis
Osteoarthritis is a degenerative arthritis that tends to get worse with age. Injury to this joint can in some cases, develop into osteoarthritis, which can cause pain and stiffness. Osteoarthritis is normally treated with rest, physiotherapy and anti-inflammatory medications. If the symptoms of osteoarthritis do not respond to this cause of treatment then surgery may be needed.
READ MORE ABOUT:
Anatomy of the Scapula
Anatomy of the Clavicle
Sternum anatomy
Shoulder Anatomy
Sterno-Clavicular Joint Anatomy
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