The shoulder is one of the largest and most complex joints in the body. The shoulder joint is formed where the humerus (upper arm bone) fits into the scapula (shoulder blade), like a ball and socket. Also, it consists of other important bones in the shoulder. One of the main joints is Sternoclavicular Joint.
The sternoclavicular joint or sternoclavicular articulation is the joint between the manubrium of the sternum and the clavicle bone. It is structurally classed as a synovial saddle joint and functionally classed as a diarthrosis and multiaxial joint.
It is the only true joint that connects the appendicular skeleton of the upper limb with the axial skeleton of the trunk.
It is composed of two portions separated by an articular disc of fibrocartilage. The bone areas entering into its formation are the sternal end of the clavicle, the upper and lateral part of the sternum, (the clavicular notch), and the cartilage of the first rib, visible from the outside as the suprasternal notch. The articular surface of the clavicle is much larger than that of the sternum, and is invested with a layer of cartilage, which is considerably thicker than that on the sternum.
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 ligaments 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.
The function of the sternoclavicular joint is to coordinate the movements of the upper limb with the core of the body. Thus, allowing the upper limb to perform its full range of motion. Specifically, the movements of the sternoclavicular joint are sorted into three degrees of freedom; elevation – depression, protraction – retraction, and axial rotation.
Sternoclavicular Joint Separation
The sternoclavicular joint is located where the collarbone (clavicle) attaches to the breastbone (sternum). These bones are held together by a piece of connective tissue called a ligament. A sternoclavicular separation occurs when the ligament tears.
Sternoclavicular joint dislocations are associated with the following injuries:
- Anterior dislocation – The top of the humerus is displaced forward, toward the front of the body. This is the most common type of shoulder dislocation, accounting for more than 95% of cases.
- rib fractures
- pulmonary contusion
posterior dislocation – With seizure activity, the arm is internally rotated and in the abducted position. The internal rotator muscles (teres major and subscapularis) overpower the external rotator muscles (teres minor, infraspinatus) to dislocate the head of the humerus.
- subclavian vascular injury
- esophageal injury
- cardiac arrhythmias
- brachial plexus injury
- tracheal injury
There is pain, swelling, and tenderness over the sternoclavicular joint. There may be movement between the breastbone and the collarbone. Your collarbone may be in front of or behind your breastbone.
Different SC joint problems have different symptoms.
You will know immediately if your SC joint has dislocated. Dislocation causes severe pain that gets worse with any arm movements. In anterior dislocation, the end of the clavicle juts out near the sternum. This causes a hard bump in the middle of the chest. In posterior dislocation, a bump is usually not obvious. The joint will feel different too. Posterior dislocations can cause difficulty breathing, shortness of breath, or a feeling of choking. Some patients have trouble swallowing or have a tight feeling in their throats.
Sometimes force may only sprain the SC joint. Mild sprains cause pain, but the joint is still stable. In moderate sprains, the joint becomes unstable.
In rare cases, patients have a stable joint but a painful clicking, grating, or popping feeling. This indicates an injury to the intra-articular disc ligament. This type of injury causes pain and problems moving the SC joint.
Osteoarthritis is a type of degenerative arthritis that tends to get worse with age. Injury to a joint can result in the development of osteoarthritis. Osteoarthritis eventually causes pain and stiffness. Usually, these symptoms go away with anti-inflammatory medications, rest, and heat. If the symptoms last for six to 12 months, some type of surgical treatment may eventually be needed.
The most common symptom of an SC joint disorder is a pain in the area where the clavicle meets the sternum. This pain will be present with a sprain but will be much sharper in the case of a fracture or dislocation—especially when you attempt to move your arm.
Other signs and symptoms may include:
- Swelling, bruising, or tenderness over the joint
- A crunching or grinding sound when you try to move your arm
- Limited range of motion in the arm
- With an inflammatory condition, such as rheumatoid arthritis, you may have simultaneous pain in other joints in your body
- With a joint infection, there may be redness over the joint and you may have fever, chills, or night sweats. If you experience any of the symptoms of a joint infection, it is important to seek medical attention right away.
A sternoclavicular joint separation most commonly occurs when there is a direct blow to the sternum or a fall onto the shoulder or outstretched hands that causes a force along the length of the collarbone.
Injuries to the SC joint typically result from motor vehicle accidents or participation in collision sports like football. While these injuries can be painful, most are relatively minor and will heal well without surgery. Very rarely, a hard blow to the SC joint can damage the vital organs and tissues that lie nearby. When this occurs, it is a serious injury that requires immediate medical attention.
The SC joint can also be damaged over time, as the protective tissue that covers the ends of the bones gradually wears away. This type of degenerative change in the joint can lead to pain, stiffness, and reduced motion in the shoulder and arm.