Grossly type I injuries represent minor strains of the acromioclavicular ligament and joint capsule. Type I injuries are synonymous with grade I injuries. These injuries commonly result from direct force to the shoulder. The AC ligaments and the coracoclavicular ligaments are both intact although the AC ligaments are sprained. The deltotrapezial fascia is intact. Pain is minimal. The AC joint is stable and the radiographs at the time of injury are negative though periosteal calcification at the distal end of clavicle may be apparent later. The treatment is essentially conservative.

More significant forces cause type II or grade II injuries. In this type of injury the acromioclavicular ligaments are disrupted but the coracoclavicular ligaments are intact. However some degree of sprain of the CC ligament is present. The deltotrapezial fascia is also intact. AC joint instability is present especially in the anteroposterior plane. Vertical stability is present due to the intact coracoclavicular ligaments. Considerable pain and tenderness are present. The radiographs show slight elevation of the clavicle as compared to the acromion, even on stress x-rays. Due to some element of medial rotation of the scapula at the AC joint, there can be widening of the AC joint. The deformity and the instability become apparent on application of stress. These injuries are also managed conservatively with good results and only sparingly needing surgery.

This injury is characterized by rupture of both the acromioclavicular and the coracoclavicular ligaments. These are caused by forces which are strong enough to cause injury and disruption of both ligaments. Literature mostly says that the deltoid and trapezius muscles are intact and there is no significant disruption of the deltoid or trapezial fascia. Pain is severe on movements. The acromioclavicular joint is disrupted and the clavicle is displaced superiorly. There is gross instability of the acromioclavicular joint in both horizontal and anteroposterior planes. The stress views demonstrate that the distal clavicle is separated from the acromion and displaced superiorly. The radiographs show 25–100 % increase in the coracoclavicular space as compared to the normal side. The superior displacement of the clavicle is due to inferomedial drooping of the shoulder complex and the scapula. There are two schools of thoughts on the treatment of these injuries. Some surgeons advocate operative treatment but many orthopedicians give trial of a conservative treatment and go for surgery only when there are residual or persistent symptoms after 3–6 months. The physical status and the patient demands are also an important factor in deciding the treatment of these injuries. The author’s preferred treatment is also conservative initially with a close watch on the condition. In athletes also the same protocol is practiced by the author as the rehabilitation phase is very difficult in athletes after surgery.

This injury is characterized by posterior displacement of the clavicle through the trapezius muscle. The force acting on the acromion drives the scapula anteriorly and inferiorly causing the posterior displacement of the clavicle. Both the acromioclavicular and the coracoclavicular ligaments are torn. The trapezial and the deltoid fascia are disrupted with the detachment of the deltoid and trapezius muscles. The clavicle may tent the posterior skin sometimes. The AP x-rays may be misleading as they may appear normal, although the axillary x-rays demonstrate the posterior displacement of the clavicle. CT scan is often required for delineation of these injuries. An important point to be noted with these injuries is that they are associated with the anterior displacement of the sternoclavicular joint. Thus in every case of type IV acromioclavicular injury, the sternoclavicular joint should be evaluated and imaging done. These injuries are relatively rare.

These injuries are severe forms of type III injuries when the deforming force is of a high amplitude. The acromioclavicular and the coracoclavicular ligaments are disrupted and the acromioclavicular joint is extremely unstable in both directions. The deltoid and the trapezius muscles are detached. The clavicle goes superiorly and the displacement is extreme. There is severe superior migration of the distal clavicle due to the unopposed action of the sternocleidomastoid along with drooping of the shoulder complex and scapula leading to marked disfigurement of the shoulder. The radiographic coracoclavicular distance is increased more than 100 % in comparison to the normal side. Some authors have suggested that there is a change in acromioclavicular distance of 100–300 % on radiographs [2] as compared to 25–100 % increase in the distal acromion-clavicle distance as seen in type III injury.

These injuries are extremely rare. Gerber and Rockwood [15] have reported three cases and this series is the largest one reported in the literature. The injury is characterized by inferior dislocation of the clavicle. The injury represents severe trauma and is frequently associated with a number of other injuries. The injury is thought to be caused by hyperabduction and external rotation of the arm along with retraction of the scapula. The clavicle is inevitably found in either a subacromial or subcoracoid position. The ligament status and muscle injury depend on the displacement of the clavicle. In a subcoracoid position both the acromioclavicular and the coracoclavicular ligaments are disrupted and there is variable degree of damage to the deltoid and the trapezius muscles. The clavicle dislodges behind an intact conjoint tendon. In the subacromial position the acromioclavicular ligaments are torn but the coracoclavicular ligaments are intact. Most patients have associated paresthesia with the injury which resolved on relocation of the clavicle.

The main symptom is pain and the main sign is tenderness located at the AC joint though swelling and deformity often accompany pain and tenderness. Any attempt to move the shoulder causes pain. The pain and tenderness increase with increase in the grade of dislocation. Abnormal protuberance of the distal end of the clavicle can be found with grade III or grade V acromioclavicular joint dislocations. Instability in the horizontal plane as well as the vertical plane can be assessed depending upon the grade of dislocations (described with the grades of dislocations) (Fig. 23.2).

The treatment of acromioclavicular joint injuries varies according to the severity or grade of the injury and patient requirement.

The objective of treatment – operative or nonoperative – is to attain a pain-free shoulder with full range of motion, full power, and no limitation of activities. The demands differ from the general population to athletes and recreational athletes to professional athletes and these demands play an important role in deciding the management of the injury. However, there are few peer-reviewed studies of the treatment of AC joint injuries in athletes. No prospective studies compare the operative and nonoperative treatment in type III AC injuries in the group of patients. Thus there are no absolute indications for either type of treatment of this injury in athletes.