THE CLINICAL SYNDROME

• Both sudden and gradual forces of force, known as microtrauma and macrotrauma, are capable of causing damage to the acromioclavicular joint.

• When playing sports or riding a bicycle, falling directly onto the shoulder is a common cause of acute injuries.

• These injuries can be particularly severe.

• Trauma to the joint can also be caused by repetitive strain, such as that which occurs when throwing or working with the arm raised across the body.

• Following an injury, the joint may experience acute inflammation; however, if the condition persists for an extended period of time, arthritis of the acromioclavicular joint may eventually develop.

• Cysts that form in the acromioclavicular joint have the potential to grow quite large, which can lead to functional disability as well as pain.

• Infection of the acromioclavicular joint is an extremely unusual occurrence.

SIGNS AND SYMPTOMS

• When reaching across the chest, patients who suffer from a dysfunction of the acromioclavicular joint frequently complain of pain in the affected joint.

• Patients frequently report that they are unable to sleep on the affected shoulder, and they may also complain of a grinding sensation in the joint, particularly upon initially waking up in the morning.

• During a physical examination, the affected joint may be found to be enlarged or swollen, in addition to being tender to the touch.

• The affected shoulder may experience an increase in pain when subjected to downward traction or passive adduction.

• An abnormal acromioclavicular joint will show positive results on a series of provocative tests during a physical examination.

• These tests include the acromioclavicular adduction stress test, the chin adduction test, and the Paxino test.

• These maneuvers have the potential to reveal that the acromioclavicular joint is actually unstable if its ligaments have been compromised in any way.

TESTING

• The joint may show signs of narrowing or sclerosis on plain radiographs, which is consistent with osteoarthritis or actual separation or dislocation of the joint.

• If there is a suspicion that the ligaments have been disrupted, magnetic resonance imaging (MRI) should be performed to determine the full extent of the ligamentous injury and to assist in ruling out the possibility of infection.

• The acromioclavicular joint can be evaluated with ultrasound, which is helpful in further defining the pathology of the joint.

• The injection technique that will be described later can be utilized both as a diagnostic tool and a treatment strategy.

• Arthroscopy of the joint can provide additional diagnostic information in some patients, but only in certain cases.

• Screening laboratory tests including a complete blood count, erythrocyte sedimentation rate, and antinuclear antibody testing should be carried out in the event that polyarthritis is present.

DIFFERENTIAL DIAGNOSIS

• Shoulder pain is frequently brought on by osteoarthritis of the acromioclavicular joint, which is typically brought on as a result of some kind of injury.

• However, rheumatoid arthritis and rotator cuff arthropathy are also common causes of shoulder pain, and both of these conditions can cause symptoms that are very similar to those associated with the acromioclavicular joint, which can make the diagnosis more difficult. Shoulder pain brought on by arthritis can also be caused by collagen vascular diseases, infections, and Lyme disease, although these are less common causes.

• Treatment for acute infectious arthritis typically consists of culture, antibiotics, and surgical drainage rather than injection therapy.

• This is because acute infectious arthritis is typically accompanied by significant systemic symptoms, such as fever and malaise. Shoulder pain that is caused by collagen vascular disease responds exceptionally well to the intraarticular injection treatment technique.

• However, collagen vascular diseases typically manifest as polyarthropathy rather than monarthropathy that is limited to the shoulder joint.

TREATMENT

• The initial treatment for the pain and functional disability associated with acromioclavicular joint pain consists of a combination of physical therapy and nonsteroidal anti-inflammatory drugs (NSAIDs) or cyclooxygenase-2 (COX-2) inhibitors. Both of these classes of medications are commonly known as COX-2 inhibitors.

• The application of heat and cold to specific areas of the body may also be beneficial.

• Patients who do not respond to these treatment modalities may benefit from an intraarticular injection of a local anesthetic and steroid as the next logical step in the treatment process.

• When administering an intraarticular injection into the acromioclavicular joint, the patient is first positioned in the supine position, and then an antiseptic solution is used to prepare the skin that lies over the superior shoulder and distal clavicle.

• A sterile syringe with 1 milliliter (mL) of bupivacaine that does not contain any preservatives and 40 milligrams (mg) of methylprednisolone is threaded onto a needle that is 11.2 inches long and 25 gauges in diameter using aseptic technique.

• After locating the acromion's apex, the next step is to locate the acromioclavicular joint space, which can be found approximately one inch medially from the acromion's apex.

• After passing through the skin and the subcutaneous tissues, the needle is then carefully inserted into the joint after passing through the joint capsule.

COMPLICATIONS AND PITFALLS

• If the clinically relevant anatomy is carefully considered before administering the injection, this method does not pose a safety risk.

• In order to prevent infection, sterile technique must be utilized, and universal precautions must be taken in order to lessen the likelihood that the operator will be put in harm's way.

• If pressure is applied to the injection site immediately after the injection, this can help reduce the risk of complications such as ecchymosis and hematoma formation.

• Infection is the most significant risk associated with intraarticular injection of medication into the acromioclavicular joint; however, if proper aseptic procedure is followed, the risk of infection should be extremely low.

• After receiving an intraarticular injection in the acromioclavicular joint, approximately one quarter of patients experience a temporary increase in the level of pain they are experiencing. Patients should be made aware of the possibility that this will occur.