I. What is the acromioclavicular joint? The acromioclavicular joint, or acromioclavicular-clavicular joint, is the joint above the shoulder that connects the clavicle to the scapula (scapular girdle). The acromion is part of the scapula, a bony prominence above the shoulder that can be touched. At the acromioclavicular joint, there are strong ligaments that attach the acromion to the clavicle; in between there is a cartilage disc that acts as a padding. The acromioclavicular joint is very important because it connects the scapular girdle to the rest of the bones of the torso. This is a common site for shoulder pain and is often damaged. What causes acromioclavicular joint pain? Normally, there is a cartilage disc between the acromion and the clavicular end of the acromioclavicular joint. This disk acts as a cushion during shoulder movement and allows the acromion and clavicle to rotate relative to each other. However, sometimes this disk can degenerate, resulting in the loss of the cushion; sometimes the disk can be damaged by a fall on the shoulder, repetitive overhead motion, or trauma such as weight lifting. This can lead to pain and sometimes mechanical symptoms such as popping or catching. Inflammation of the acromioclavicular joint may develop into a condition called osteolysis, which is a degenerative change in the resorption of the bone ends within the joint. This condition is often seen in people who lift weights. Sometimes the pain stems from painful arthritis. Arthritis may be a normal manifestation of old age, or it may be caused by trauma or repeated excessive joint loading. The latter is often referred to as traumatic arthritis. C. What can cause a shoulder lock joint injury and how can the shoulder lock joint separate? The acromioclavicular joint is a frequent site of injury. A common mechanism of injury is a fall on the top of the shoulder or from a specific sport, such as a blocking impact on the top of the shoulder joint suffered by a player in North American rugby or an impact of the shoulder with a protective plate in field hockey. The acromioclavicular joint has strong ligamentous connections. These ligaments run between the acromion and the clavicle (acromioclavicular ligament) and between the rostral process and the clavicle (rostral ligament). These ligaments may be stretched without rupture (type I injury), partially torn (type II injury), or completely torn (type III, IV, or V injury). Pain after an injury to the acromioclavicular joint may originate from the stretched or torn ligaments or from damage to the cartilage discs within the joint. If the ligament is torn severely, it can lead to a deformity of the acromioclavicular joint, which means that the lateral end of the clavicle is buckled. This is because the clavicle loses its normal suspension support for the arm, the shoulder and arm drop, and the lateral end of the clavicle appears to protrude, commonly referred to as a “detached acromioclavicular joint”. Patients with acromioclavicular joint separation may experience acute or dull pain in the shoulder joint, and may feel a misalignment or instability in the acromioclavicular joint. 4. How is acromioclavicular joint pain treated? There are many ways to treat pain from shoulder lock joint inflammation or osteolysis. The first step is to use conservative treatment, including rest, avoiding activities that can cause joint pain, taking anti-inflammatory and analgesic medications, using local heat and cold treatments, and regular physical therapy measures including ultrasound. If conservative treatment is not effective in relieving pain, hormone and anesthetic injections into the acromioclavicular joint can be helpful. Local injections generally serve two purposes: first, they reduce inflammation, and many patients experience significant pain relief as a result; second, they confirm that the acromioclavicular joint is the site of pain production if the pain is relieved after the injection. If, despite conservative treatment, pain persists and affects the patient’s quality of life, surgical treatment is required. Surgery involves removing the lateral end of the clavicle and a small portion of the medial border of the acromion and removing the cartilage disc, which creates a space so that there is no irritating contact with the articular surface of the acromioclavicular joint. The surgery can be done arthroscopically or through an incision, both with the same results. V. How is a detached acromioclavicular joint treated? The treatment of acromioclavicular joint separation has always been controversial. Most acromioclavicular joint separations can be treated conservatively. Type I and type II injuries are best treated conservatively. Patients with type III injuries can be treated conservatively if they are comfortable with the protrusion of the clavicular end, if the pain is not severe, and if function is not compromised. Some physicians may recommend immediate surgery with screws or sutures to stabilize the acromioclavicular joint; however, there is a lack of clinical experience in the literature to support this management. In more severe acromioclavicular joint separations, such as type IV and V injuries, the chances of pain and dysfunction with conservative treatment are very high, and the logical choice is immediate surgery. If the acromioclavicular joint separation is old (several months old), reconstruction of the ligament between the scaphoid and the clavicle is usually required. The surgery can be performed with a localized ligament of the shoulder joint or with an allograft ligament, with combined suture application. The procedure can be done with arthroscopic assistance or as a complete incision.