The bones that make up the shoulder are the upper end of the arm bone (humerus), the shoulder blade (scapula), and the collarbone (clavicle). Some would describe this joint as a ball and socket joint, but it is more like a ball sitting on a golf tee, meaning that there is a tiny surface area of bone contact. The stability of the shoulder joint relies heavily on the soft tissues around the bone, including muscles, tendons, capsule, and labrum, that keep the arm centered with the shoulder blade. The collarbone or clavicle is another structure in the shoulder region that attaches to the shoulder blade at the front of the shoulder; this joint is called the acromioclavicular joint (AC joint).
The ends of our bones are covered in a protective layer of tissue called cartilage. It allows two or more bones to slide against each other smoothly, which makes up a joint. Damage to the cartilage from injury or normal wear-and-tear can cause pain and stiffness in the shoulder joint. Other conditions such as rotator cuff tear, chronic instability, and infection can lead to arthritis as well. In most cases, arthritis develops slowly and generally worsens with time.
This is commonly known as arthritis, caused by the “wear-and-tear” of the joint. It most commonly affects people aged 50 or older. With time and frequent use, the cartilage wears down and frays, causing inflammation in the joint. Advanced osteoarthritis leads to complete or near-complete loss of the protective surfaces of the joint, leading to an appearance of “bone-on-bone,” easily seen on x-rays. This can occur in the ball and socket joint of the shoulder, the glenohumeral joint. It may also occur in the joint where the clavicle meets the acromion, the acromioclavicular joint (AC joint).
This is a chronic disease where the immune system attacks multiple joints. This disease damages the cartilage, tendons, ligaments, and soft tissues around the joint. It also causes swelling of the synovium, a delicate structure that encapsulates a joint that lubricates the joint. It also softens the bones. This chronic inflammation, over time, will cause deformity to the joint, which limits shoulder function and is typically very painful. Symptoms are usually symmetric, meaning it affects both left and fitting joints, in this case, both shoulders.
Rotator Cuff Arthropathy
A rotator cuff is a group of muscles responsible for shoulder movements. They lift the arm, help rotate it, and allow you to pull objects toward you. Injuries to the rotator cuff can cause instability, meaning that the upper part of the arm may not sit properly against the glenoid of the shoulder blade. This causes damage to the cartilaginous surface as the bones move against one another.
Fractures of the humerus, scapula, or clavicle occur after traumatic injury. In younger patients, this can be a fall from a height or other high-energy accidents such as car accidents. In older patients with lower bone density, a typical energy injury may cause a fracture, for example, a trip and fall. Fractures can be treated with or without surgery depending on factors such as fracture patterns, whether or not there is an open wound around the fracture site, amount of fractures present, joint alignment, and overall positioning of the fracture.
Fractures that extend to the ends of the bone and break through the cartilage may lead to chronic inflammation in the joint. The more displacement in the joint surface, the higher the likelihood of developing arthritis after these traumatic accidents.
Avascular necrosis of the shoulder occurs when there is damage or disruptions to the blood supply to the head of the humerus (the ball of the ball and socket joint of the shoulder). If the bone does not have sufficient blood to survive, it will die and begin to collapse, damaging the cartilage. The resulting condition is a severely deformed joint that is very painful and stiff.
Some causes of avascular necrosis include high-dose steroid use, excessive alcohol consumption, sickle cell anemia, and trauma/fractures. In some cases, there are no identifiable causes of avascular necrosis.
A medical practitioner may examine the shoulder to check for a range of motion, apply pressure to various areas of the shoulder to see if this causes pain, and check nerve function in the muscles and skin of the arm/hand. Special tests may be performed to evaluate for specific shoulder conditions, like the ones mentioned above.
Based on the history of the shoulder symptoms and the practitioner’s physical examination, imaging can be beneficial in identifying the critical cause of the shoulder complaint. X-rays are very effective in evaluating and monitoring the healing of fractures and dislocations. They may also aid in assessing the degree of arthritis.
A CT scan may give finer detail regarding fractures and bony abnormalities of the shoulder.
MRI is best for evaluating soft tissue injuries like rotator cuff or labral tears.
Treatment of shoulder pain, stiffness, and instability will depend on the root cause of the symptoms. Some conditions may be best treated without surgery. Rest, medications, exercises, or physical therapy may be adequate for many diseases, such as frozen shoulder, tendonitis, and bursitis. Some forms of treatment may help to address pain and inflammation in or around the joint such as injections. Some tears or fractures may need surgery to heal well.