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Five progressive clues
These are the case findings in their original reveal order, moving from the broader presentation to the most discriminating evidence.
Clue 1
A 24-year-old competitive road cyclist arrives at outpatient physical therapy five days after crashing during a weekend criterium, flipping over his handlebars and landing squarely on the top of his right shoulder. He is right-hand dominant and sheepishly admits he is more worried about missing next month's race than about the pain. His chief complaint is a persistent ache at the very top of that shoulder.
Clue 2
The pain began the instant he hit the pavement, is sharp and pinpoint over the top of the shoulder, and has not radiated into his neck or down the arm. He has no numbness or tingling in the hand. It flares when he reaches across his body to buckle a seatbelt or wash the opposite armpit, and when he lies on that side at night, and it eases when he simply lets the arm hang at his side.
Clue 3
On examination, tenderness is exquisitely localized to the small joint at the outer end of the collarbone, not to the deltoid or the joint line beneath it. Horizontal cross-body adduction reproduces his pain precisely at that spot, while resisted rotator-cuff testing is strong and pain-free and there is no painful mid-range arc during elevation.
Clue 4
Bilateral standing radiographs show no fracture, but on the injured side the outer end of the collarbone rides visibly higher than the tip of the shoulder blade, and the gap between the collarbone and the coracoid process is clearly wider than on the uninjured side.
Diagnosis
Acromioclavicular Sprain
Why the diagnosis fits
A direct blow to the top of an adducted shoulder (landing on the point of the shoulder), pinpoint tenderness over the joint at the outer end of the clavicle, pain on horizontal cross-body adduction with an intact and painless resisted cuff exam, and radiographs showing the distal clavicle riding superior to the acromion with a widened coracoclavicular interval all localize the injury to the joint between the clavicle and the acromion. The confirmatory reveal is a reducible superior step deformity: the raised distal clavicle depresses under pressure and springs back when released, and supporting the elbow upward off-loads the joint and relieves pain. The single key discriminator from rotator cuff pathology is that pain and tenderness stay precisely over the distal clavicle with a strong, pain-free resisted cuff and no painful mid-range arc, together with a mechanically reducible step deformity rather than abduction weakness.
Educational reference
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