Classification and diagnosis of the acromioclavicular sprains are based on the extent of involvement of the injured ligaments.
■ Grade I sprains of the acromioclavicular joint are the result of a mild force with only a few fibres of the acromioclavicular ligament and capsule involved. There is no laxity of the acromioclavicular joint. Pain is minimum, although point tenderness usually can be elicited over the acromioclavicular joint. The roentgenogram is negative initially, but later it may show subperiosteal calcification about the distal end of the clavicle.
■ Grade II sprains (Fig. 34a) are usually the result of a moderate force which causes rupture of the capsule and acromioclavicular ligament. This injury frequently is referred to as a subluxation. There is no rupture of the coracoclavicular ligaments. Pain and tenderness are lo-
calized over the acromioclavicular joint, and laxity is present in the joint, frequently causing deformity. Roentgenograms reveal the clavicle riding higher than the acromion, but to an extent that is usually less than the width of the clavicle, even while downward stress is applied to the arm. Whenever an acromioclavicular-joint injury is suspected, stress roentgenograms of both shoulders with a 10- to 15-pound weight suspended from each wrist should be included in the work-up.
■ Grade III sprains of the acromioclavicular joint (Fig. 34b) are usually the result of a severe force with rupture of both the acromioclavicular and coracoclavicular ligaments. This injury frequently is referred to as a dislocation. Pain and tenderness are noted over the acromioclavicular joint and usually over the distal third of the clavicle and cora-coid process. Deformity is obvious, and the distal end of the clavicle is easily palpable and ballotable. On the roentgenogram, the distal end of the clavicle is above the superior surface of the acromion, and the distance between the clavicle and coracoid process is increased.
Special mention should be made of posterior displacement of the distal end of the clavicle. The mechanism of injury is usually a direct blow on the distal end of the clavicle; however, the injury may result from a fall on the posterosuperior aspect of the shoulder. This condition frequently is missed because, even on stress roentgenograms, the clavicle may not show an upward displacement.
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