Injuries in and around the shoulder, including acromioclavicular joint injuries, occur most commonly in active or athletic young adults. However, paediatric acromioclavicular injuries have also increased owing to the rising popularity of dangerous summer and winter sporting activities. Proper knowledge of the different problems and treatment options for shoulder disorders is necessary to help patients return to their preinjury state.

The acromioclavicular joint is a plane type synovial joint. It is located where the lateral end of the clavicle articulates with the acromion of the scapula. The joint can be palpated during a shoulder examination; 2-3cm medially from the ‘tip’ of the shoulder (formed by the end of the acromion).

In this article, we shall look at the anatomy of the acromioclavicular joint – its articulation, ligaments, neurovascular supply, and any clinical correlations.

Structure:

The joint is stabilized by three ligaments:

Superior Acromioclavicular Ligament:  This ligament is a quadrilateral band, and extending between the upper part of the lateral end of the clavicle and the adjoining part of the upper surface of the acromion.

It is composed of parallel fibers, which interlace with the aponeuroses of the Trapezius and Deltoideus; below, it is in contact with the articular disk when this is present.

Inferior Acromioclavicular Ligament:  This ligament is somewhat thinner than the preceding; it covers the under part of the articulation and is attached to the adjoining surfaces of the two bones.

The Coracoacromial Ligament is a strong triangular band, extending between the coracoid process and the acromion.

The 2 coracoclavicular ligaments (the conoid and the trapezoid ligaments) are found medial to the acromioclavicular joint and attach from the coracoid process on the scapula to the inferior surface of the distal clavicle. These ligaments provide vertical (superior-inferior) stability to the joint.  The compression of the joint is restrained mainly by the trapezoid ligament. The deltoid and trapezius muscles are especially important in providing dynamic stabilization when these ligamentous structures are damaged.

Torn acromioclavicular joint ligaments and/or torn coracoclavicular ligaments are seen in acromioclavicular joint sprains. The meniscus that lies in the joint may also be injured during sprains or fractures around the acromioclavicular joint.

Symptoms:

  • Swelling
    When arthritis causes friction between bones, the surrounding soft tissue can become irritated and swell. Swelling at the top and front of the shoulder is sometimes seen in people with AC joint arthritis.
  • Pain with certain motions:
    People with acromioclavicular arthritis have difficulty with cross-body arm movement—holding the arm out straight and then moving it in a horizontal plane across the body, toward the other shoulder. Reaching up and across the body to put on a car seat belt can pose a challenge.

A person may also have pain when performing a bench press or push up, reaching behind the back, or reaching overhead.

  • Joint tenderness and pain:
    The spot where the scapula and clavicle meet, located at the front and top of the shoulder, may feel tender and painful. (Alternatively, tenderness and pain that is isolated to the back of the shoulder may be a sign of arthritis in the glenohumeral joint, commonly known as the shoulder’s ball-and-socket joint.)
  • Radiating pain:
    It is possible for arthritis pain that originates at the AC joint to radiate into the rest of the shoulder, the base of the neck, or arm. Pain that radiates to the base of the neck may lead to headaches.
  • Inactivity makes it worse
    The joint area can become stiff after long periods of inactivity and get better after short bouts of activity.
  • Trouble sleeping
    Laying on the affected shoulder can be painful. Many people decide to go to the doctor when shoulder pain begins to interrupt sleep.
  • Crepitus
    The shoulder may produce a clicking, popping, snapping, or crunching sensation when stress is put on it. The medical term for this symptom is called crepitus.

In most but not all cases, the symptoms of AC joint osteoarthritis come and go, becoming worse and more frequent over months or years. Acromioclavicular osteoarthritis pain may flare up after high-intensity activities, such as tennis or weightlifting.

Causes:

 

  • Joint trauma:
    Serious injury or surgery can cause damage to the acromioclavicular (AC) joint and eventually lead to acromioclavicular osteoarthritis, although symptoms may not appear for months or even many years later.
  • Joint stress and chronic injury:
    People who spend a lot of time lifting objects overhead can experience “mini-traumas” in their shoulder joints and are more likely to develop acromioclavicular osteoarthritis. People who have spent years weightlifting or participating in high-impact sports, such as hockey, also can be particularly prone to acromioclavicular osteoarthritis.
  • Congenital defect or illness:
    Poor bone alignment can increase the risk of shoulder separations, thereby increasing the likelihood of developing osteoarthritis of the shoulder. Other congenital conditions, metabolic disorders, and episodes of gout or septic arthritis can also increase risk.
  • Advanced age:
    Cartilage weakens with age, which is why osteoarthritis in all joints is more common in older people. Research suggests many people who are middle-aged and older have AC joint osteoarthritis, though many do not have painful symptoms.

Types of AC joint injuries:

The type of shoulder separation depends on how much you tear the Acromioclavicular (AC) joint or coracoclavicular (CC) ligaments that hold the joint in place.

  • Type I = the AC ligament is slightly torn, but there’s no damage to the CC ligament is unharmed.
  • Type II = the AC ligament is completely torn, and there’s little or no tear to the CC ligament.
  • Type III = both the AC and CC ligaments are completely torn. In this case, the collarbone separates from the end of the shoulder blade.

Three more types of AC joint injury are also possible, but rare. These involve tearing of the ligaments and surrounding muscle tissue.

Shoulder separation or AC joint injury causes:

Shoulder separation often happens because of a hit too:

  • The tip of your shoulder.
  • The top part of your shoulder.
  • Your outstretched arm.

You may damage the AC joint or rotator cuff from a fall or tackle during a game.


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