AC joint separations are caused by a sudden impact or trauma, usually falling onto an outstretched arm. Symptoms will vary depending on severity of the injury.
AC joint sprains are graded 1 to 6 with grade 1 being a mild injury and grade 6 a severe sprain resulting in complete ligament rutpures.
Symptoms include sudden onset of pain at the time of injury, often as a result of a fall onto the shoulder or onto an outstretched arm. Or from direct impact in a collision sport. Moving the arm above the head is likely to be painful and the athlete is likely to suffer a significant loss of function.
There will be tenderness and swelling and inflammation over the acromioclavicular joint itself. When pressing in there will be point tenderness over the site of injury. In particular the athlete is likely to have pain on moving their arm out to the sides and upwards (abduction). With more severe injuries a visible deformity in the form of a lump or bump on top of the shoulder is likely.
Grading of injuries
AC joint injuries are graded from 1-6 using the Rockwood scale which classifies injuries in relation to the extent of ligament damage and the space between the acromion and clavicle.
Grade 1 is a simple sprain to the AC joint with minor damage to the ligament and no separation of bones.
Grade 2 involves rupture of the AC ligament or acromioclavicular ligament.
Grade 3 rupture of both AC and CC or coracoclavicular ligaments which often results in an upwards displacement of the clavicle bone.
From this point onwards the scale and grade of injury depends on the degree of displacement of the clavicle.
Grade 4 involves posterior displacement or displacement backwards.
Grade 5 superior displacement, to a greater degree than grade 3, with an increase in coracoclavicular space by 3-5 times the norm. A step deformity may be apparent with grade 3, 4 & 5 injuries.
Grade 6 involves full rupture of both AC and CC ligaments with the clavicle being displaced inferiorly or downwards.
A professional therapist may do a number of special tests to confirm the diagnosis:
Distracion test (piano key sign) involves the athlete sitting with both arms relaxed down by their sides. The professional therapist or athletic trainer pulls down on the wrists and looks for a 'hollowing out' just behind the joint.
Crossover test - the therapist or trainer abducts (moves) the athletes arm across the front the the body whilst compressing the joint.