Shoulder injuries, especially to the acromioclavicular joint (AC joint), are common occurrences in car accidents, particularly to the shoulder restrained by a seat belt.
The acromioclavicular joint or AC joint is one of the joints on top of the shoulder. It provides the connection between the acromion and the clavicle. The acromion is actually part of the scapula that sticks up above the shoulder.
The AC joint is the part of the shoulder that allows a person to raise the arm above the head. It is called a sliding synovial joint and helps the shoulder have an increased range of motion.
There are three ligaments that stabilize the joint:
• The acromioclavicular ligament
• The coracoacromial ligament
• The coracoclavicular ligament
The ligaments act together to keep the joint relatively stationary.
What is an acromioclavicular injury?
An acromioclavicular joint injury is also called an acromioclavicular separation or an AC joint separation. It occurs with trauma to the shoulder and leads to difficulty raising the arm above the shoulder.
There are six types or degrees of AC joint separation. These include:
• Type I injury. This involves a partial tear or strain in the AC ligaments and no problem with the CC ligaments. The AC joint is tender and there is mild swelling of the joint itself. They tend to heal without treatment within a few weeks.
• Type II Injury. This involves having a complete tear in the AC joint with a partial tear or sprain of the coracoclavicular ligaments (CC ligaments). There is tenderness and a great deal of swelling of the area.
• Type III Injury. In this type, there is a complete tear of both the AC and the CC ligaments. The AC joint will look out of place. There is a lot of tenderness and tenderness of the CC joint area. Such an injury takes up to several months to heal.
• Types IV, V and VI. These involve increasing separation of the joint and all usually need some type of surgery.
When the AC joint separates, it can heal completely or it can lead to arthritis of the AC joint, frozen shoulder, and chronic pain in the upper part of the shoulder.
Most injuries to the AC joint happen in males who are in their mid-20s. Because these injuries are so common and not all people seek medical attention, there is no exact data as to the percentage of people who get these injuries but it is believed to be a common injury in people who play high-impact contact sports. In one study, it was found that forty-one percent of college-age football players had suffered some type of AC joint injury.
What are the Symptoms of an AC Joint Injury?
People will usually present with a story of trauma directly to the shoulder and will experience pain over the lateral aspect of the lateral shoulder. There is usually extreme tenderness of the AC joint. If there is clavicular separation, there will be a visible and a palpable step off at the level of the AC joint. It is best seen with the arm hanging down from the shoulder.
The position of the clavicle needs to be determined across its entire length as an AC joint separation can occur in the presence of a clavicular fracture or even injury to the sternoclavicular joint.
Doctors should assess the patient for the presence of radial and brachial pulses along with motor and sensory abilities of the arm as an AC joint separation can damage the axillary and subclavian blood vessels, as well as the brachial plexus.
Complications of an AC joint separation can occur at the time of injury, which include:
• Brachial plexus injury and resultant pain and numbness to the arm.
• Damage to the axillary or subclavian vessels with a loss of circulation to the arm.
• Avulsion of certain muscles, in particular the deltoid and trapezius muscles.
• Pneumothorax is rare but can happen if the clavicle is fractured.
The differential diagnosis of things that could mimic an AC joint separation include:
• Shoulder separation at the level of the glenohumeral joint.
• Clavicular fracture
• Bursitis of the bursae around the AC joint
• Cervical spine fracture with radiating pain.
• Tendonitis of tendons around the AC joint
• Miscellaneous causes of shoulder pain, such as arthritis of the joint
What are the Causes of an AC Joint Injury?
An AC joint separation usually occurs in situations of a direct fall onto the tip of the shoulder. The forces from the fall travel directly through the scapula, pushing it down. Because the collarbone is an immobile bone, the force tends to separate the joint at the level of the AC joint. Greater forces can actually fracture the scapula or do damage at the sternoclavicular joint. The force pulls at and tears the AC joint.
The injury can happen in motor vehicle accidents or in sports like football and hockey. In fact, nearly half of all sports injuries related to the shoulder involve an AC joint injury. Sports involving throwing of a ball or weight lifting can cause repetitive injury to the joint and can also cause lateral clavicular fracture. Certainly, a fall from a height onto the tip of the shoulder can cause an AC joint separation. Other causes of similar pain to AC joint disruption is osteoarthritis of the AC joint, which could have come from a past AC joint injury.
Risk Fractures of an AC Joint Injury
One study looked at 162 patients with a new AC joint injury. The overall risk of joint injury was 9.2 per 1000 person-years. Most sprains were low grade; however, 17 patients suffered a high grade injury. Males were twice as likely as females to sustain an AC joint injury. Injuries occurred more likely in intercollegiate sports than in intramural sports at a 2 to 1 ratio. Sports that had the highest rate of injury were hockey, rugby, football and wrestling.
The average number of days lost due to injury in a low grade sprain was 10.4 days. This compared to 64 days lost in high grade injuries. Patients with high grade injuries had a 19 times greater rate of needing surgery when compared to low grade injuries.
Diagnosis of an AC Joint Injury
The diagnosis of an AC joint separation is relatively simple. A thorough history can pinpoint the moment of injury, which is usually a direct blow or fall onto the tip of the shoulder with pain atop and to the lateral aspect of the joint. A physical examination can show a step off of the joint and tenderness upon palpation of the joint.
A plain film x-ray may be normal in cases of low grade AC joint injury. In high grade injuries, the joint can clearly be seen as separated using a plain film x-ray. One way to exacerbate the separation and more clearly define it on x-ray is to have the patient stand carrying a weight in the affected arm’s hand. This pulls down the acromion and increases the separation of the AC joint, better showing the separated joint.
Treatment of an AC Joint Injury
The treatment used in AC joint injuries depends on how severe the injury is. In the beginning, pain control with anti-inflammatories is necessary, along with ice packs to the affected area and a sling to allow for immobility of the joint and to handle the weight of the arm. As the pain improves, it is vital that the patient begin moving the fingers, elbow and wrist in order to prevent these joint from getting stiff. Narcotic pain medication can be used, especially in the beginning of the injury. When the pain has improved, there should be a gentle range of motion of the shoulder.
Undisplaced AC joint injuries need rest, ice, pain relief, and a gradual improvement in activity level over a period of about 2-6 weeks. If the dislocation is significant, surgery is required to make the joint stable, especially in athletes attempting to return to their sport.
In Type I and Type 2 injuries, only an ice pack, sling, and anti-inflammatories need to be used. Doctors try to obtain early motion of the shoulder to keep it from stiffening. The pain usually gets better in about 10 days. As the patient’s symptoms permit, increased activity is prescribed. In some cases, the AC joint can be taped to take the stress off the AC joint.
The patient can return to the playing of his or her sport at a time that depends on what type of sport the patient plays. Those who must play with their arm above their head need to delay the start of playing again. Protection of the AC joint needs to happen through the use of a doughnut-shaped pad that lies over the AC joint to keep it from taking the brunt of the trauma to the area.
Certain type II injuries can develop late changes consistent with degenerative joint disease. These people will need resection of the distal end of the clavicle in order to relieve the pain. In athletes who have this done, there can be heterotopic bone formation beneath the clavicle which can lead to pain that feels much like an impingement of the shoulder.
In Type III injuries, the problem is treated conservatively. Historically-speaking, these injuries used to be managed with surgery. Since the 1970s, however, the feeling among orthopedists is that conservatively-treated patients have the same functional outcome as those who have surgery. People who were treated without surgery returned to their work or sport faster than the surgically-treated group.
Exceptions to the rule include those people who perform repetitive motion of the arm, do heavy lifting and those who work with their arm above the level of the shoulder. People who have prominent clavicular ends do better with surgical repair of their AC joint separation. Surgery is often not done in those patients who play contact sports because their rate of re-injury is higher.
Type IV-VI injuries, which account for about 10-15 percent of all acromioclavicular joint dislocations, should be managed with some type of surgical intervention. If the surgery is not successful, the patient almost always faces chronic pain and disability of the shoulder.
Surgery for AC Joint Dislocations
There are four types of surgical repair of AC joint dislocations. They include:
• Acromioclavicular repair. These involve using wires, pins and other hardware to approximate the AC joint.
• Coracoclavicular repairs, which involves surgery to the coracoid process of the scapula where it connects to the clavicle.
• Dynamic muscle transfers, which involve transfers of muscle to hold down the joint.
• Distal clavicular excision, which involves removing the lateral end of the clavicle.
As with any surgery, there is risk of bleeding and infection. There is also a longer recovery time to return to normal functioning with surgery.
If the patient has had an AC joint separation that is still painful after 3-6 months of conservative treatment (including rehabilitation), surgery might be indicated. In situations where the type IV-VI AC joint separation is not treated with surgery, a procedure called the Weaver Dunn technique is performed. This procedure involves taking off the lateral 2 centimeters of the clavicle and reattaching the coracoacromial ligament (acromial end) to the cut off end of the clavicle. This puts the clavicle into a more anatomical position.
After the surgery, the arm must be placed in a sling for about 6 weeks. After two weeks of immobilization, the arm will be able to be used at or below waist level. After the six week sling period, the arm is able to be used above the shoulder and passive stretching is begun. Eventually elastic straps are employed to increase the strength of the shoulder. Return to sports takes much longer than that, with most sportsmen returning to the sport after 4-6 months of rehabilitation.
Complications of an AC Joint Separation
If the AC joint doesn’t heal from a separation, there can be a permanent deformity of the top of the shoulder with a chronic bump at the level of the lateral clavicle. Ongoing pain is likely, especially when lifting the arm above the shoulder.
Osteoarthritis can occur in the joint over time. This stiffens the joint and leads to chronic disability of the affected arm.
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