Distal Clavicle Osteolysis

Distal clavicle osteolysis is a painful, non-infectious resorption of the lateral end of the clavicle that most often affects young athletic adults. It was first described in weightlifters and is still commonly called "weightlifter's shoulder", although it is now recognised in anyone who loads the acromioclavicular joint repetitively: overhead athletes, manual labourers and military personnel.

Why it matters. The condition is often misdiagnosed as rotator cuff tendinopathy, AC joint arthritis or a cervical radiculopathy. Once it is considered, the history of repetitive loading (especially bench press or overhead press) and the characteristic imaging on a Zanca view usually make the diagnosis straightforward. Most cases respond to activity modification and physiotherapy; a minority need surgical excision of the distal clavicle, which is a reliable and low-morbidity operation.

The joint. The acromioclavicular (AC) joint is a diarthrodial synovial joint between the lateral end of the clavicle and the medial facet of the acromion. A thin capsule reinforced by the superior and inferior AC ligaments surrounds it. The coracoclavicular ligaments (conoid and trapezoid) sit medial to the joint and are the main vertical stabilisers; they do not cross the joint itself but are critical to AC joint mechanics.

The disc and the load. A small meniscus-like intra-articular fibrocartilaginous disc degenerates with age; in young athletes it is still present and the joint surfaces are relatively congruent. The joint is subjected to compressive, shear and rotational forces with every overhead movement and loaded upper-limb exercise.

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The leading theory. The exact mechanism is not fully understood. The leading theory is repetitive microtrauma causing an imbalance between bone resorption and formation at the distal clavicle, and three contributions are proposed:

• Mechanical overload: high-volume bench pressing, overhead pressing, push-ups and heavy manual work apply repeated compressive and shear forces across the AC joint. The distal clavicle, with its relatively small cross-sectional area and cortical shell, is vulnerable to stress-induced bone resorption.
• Vascular compromise: some authors propose that repetitive loading impairs the subchondral blood supply of the lateral clavicle, leading to avascular bone resorption similar to osteonecrosis.
• Inflammatory cascade: microfractures and trabecular damage trigger an inflammatory response with osteoclast activation, producing the cystic change and tapering seen on imaging.

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What it is not. The process is not neoplastic, not infectious and not truly inflammatory in the sense of rheumatoid arthritis. It is a stress response of bone, and one that can stabilise or even reverse if the loading is removed.

There is no universally accepted radiographic staging system for distal clavicle osteolysis; the division that matters is by cause.

The iatrogenic form. Subacromial osteolysis beneath a clavicle hook plate is a distinct iatrogenic entity from atraumatic distal clavicle osteolysis, but it illustrates the same mechanically driven bone resorption around the lateral clavicle. Post-traumatic and iatrogenic forms are increasingly seen after AC joint stabilisation surgery.

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Describing severity. In practice severity is described by the extent of bone loss (mild tapering versus marked osteolysis) and by the response to activity modification.

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History. The typical patient is a man aged 20 to 40 years with insidious aching pain over the AC joint, often localised to the lateral end of the clavicle. In weightlifters a rapid jump in training volume or intensity precipitates symptoms, so ask about bench-press volume, overhead lifting, push-ups and training changes: the activity history is usually more revealing than any single physical sign. The pain is:

• Worse with cross-body adduction (reaching across the chest), overhead activity and pushing movements
• Exacerbated by bench press, overhead press, dips and push-ups
• Often present at night, especially when lying on the affected side

The other histories. In post-traumatic cases there is a direct blow to the point of the shoulder or a fall onto an outstretched hand. In iatrogenic cases there is previous AC joint surgery with hardware or a synthetic ligament.

Inspection and palpation. There may be subtle swelling or prominence over the AC joint, but often the shoulder looks normal. Tenderness over the distal clavicle and AC joint is the most consistent sign; palpate with the thumb posterior to the clavicle and the index finger anterior to feel the joint line.

Range of motion. Active and passive movement is usually full, with pain at the extreme of cross-body adduction and at end-range flexion and abduction.

Special tests. Each is positive when it reproduces pain at the AC joint:

• Cross-body adduction test: the arm is passively brought into 90 degrees of flexion and then adducted across the chest. Pain over the AC joint is positive; the test compresses the joint and reproduces the symptoms.
• Active compression test (O'Brien test): the arm is forward-flexed to 90 degrees, adducted 10 to 15 degrees across the body and internally rotated with the thumb down, and the patient resists downward pressure. Pain localised to the AC joint (rather than deep in the shoulder) suggests AC joint pathology.
• Paxinos test: the examiner's thumb is placed on the posterior aspect of the acromion and the index finger on the distal clavicle; squeezing them together reproduces AC joint pain.

The Zanca view. The single most important radiograph is an anteroposterior view with a 15-degree cephalic tilt, centred on the AC joint, which projects the joint clear of the scapular spine and humeral head. A standard shoulder AP may miss the changes because the joint is superimposed on both, so request a Zanca view whenever the diagnosis is suspected. It shows:

• Osteopenia of the lateral clavicle
• Subchondral cystic change within the distal clavicle
• Tapering, pointing or erosion of the lateral clavicle tip, which loses its normal squared contour
• Widening of the AC joint space, due to bone loss rather than true dislocation
• Loss of the normal cortical margin at the distal clavicle

The acromion is not always spared. Osteolysis crosses the joint to involve the anterior acromion in roughly a third of cases, more often in men and with heavier bench-press loads, so acromial change does not exclude the diagnosis.

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MRI. The best second-line investigation, indicated when:

• Radiographs are equivocal
• There is suspicion of associated pathology (rotator cuff tear, labral tear, cervical radiculopathy)
• Symptoms are atypical and the diagnosis is uncertain

It shows bone marrow oedema in the distal clavicle on fluid-sensitive sequences (T2 fat-suppressed or STIR), subchondral cystic change, joint effusion and capsular thickening, and the absence of a mass or destructive lesion, which helps to exclude tumour and infection.

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CT. Rarely needed, but it resolves subtle subchondral resorption better than plain radiographs and can delineate bone loss and cystic change when surgical planning is complex, for example after previous surgery or fracture.

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Bone scintigraphy and ultrasound. Scintigraphy is not routine, but will show focal increased uptake in the distal clavicle if performed. Ultrasound can demonstrate AC joint effusion and synovitis and guide injection, but is not diagnostic for osteolysis.

Osteolysis is only one cause of a lucent, tapered or eroded distal clavicle. The examiner's favourite trap is the patient whose film looks like "weightlifter's shoulder" but whose resorption is systemic, so know the full list and the features that should redirect you.

AC joint osteoarthritis. Arthritis also causes AC joint pain and cross-body adduction tenderness, but it shows joint-space narrowing, osteophytes and subchondral sclerosis on both sides of the joint rather than osteolysis and cystic change concentrated in the distal clavicle. Age helps at presentation but is not the discriminator it looks like, because the two are sequential rather than alternative: in athletic teenagers followed for two years after atraumatic osteolysis, 71% had developed AC joint osteoarthritis against 35% of controls, with the joint widening to a mean of 5.0 mm against 2.4 mm, and the more marrow oedema at presentation the more likely the later arthritis.

The other mimics. Rotator cuff disease declares itself with a painful arc, weakness and positive impingement signs; cervical radiculopathy is the third diagnosis this condition is mistaken for.

When the candidate says "arthroscopic excision", the examiner will ask how. There are two recognised arthroscopic routes, and each has a characteristic pitfall.

Whichever route. The principles are the same: resect roughly 5 to 8 mm, within the 5 to 10 mm principle above; confirm an even gap throughout the arc of motion, especially at the posterosuperior corner; and preserve the superior and posterior AC capsule and ligaments to protect against posterior instability. "Co-planing" (shaving the adjacent acromial undersurface to match) is optional, and many surgeons avoid it to limit bleeding and reactive bone.

Of non-operative management. The main risk is chronic pain and functional limitation if the patient continues to load the AC joint. There is no risk of malignant transformation or systemic disease.

Of surgery.

• Resection inadequacy or excess: too little leaves symptomatic bone; too much risks posterior clavicle instability
• Posterior clavicle instability: from excessive resection or loss of the superior AC ligament and capsule; presents with painful clicking and prominence
• Infection: low risk (less than 1 percent) but possible with any open or arthroscopic procedure
• Neurovascular injury: the suprascapular nerve and cephalic vein are at risk during open approaches; careful dissection avoids them
• Persistent pain: if the diagnosis was incorrect or there is associated pathology (rotator cuff, cervical spine) that was not addressed
• Deltoid detachment: specific to open approaches where the deltoid is taken off the clavicle; reattachment failure causes weakness

• Diagnosis: there is no single international guideline for distal clavicle osteolysis, but the diagnosis is established by characteristic history (repetitive loading in a young adult), physical examination (AC joint tenderness, positive cross-body adduction), and imaging (Zanca view showing osteopenia, cystic change, and tapering of the distal clavicle). MRI is widely used as a second-line test to confirm bone marrow oedema and exclude associated pathology.
• Non-operative management: activity modification is the consistent first-line recommendation across sports medicine and shoulder surgery literature worldwide. Cessation of bench press, overhead press, push-ups, and dips for a minimum of 6 to 12 weeks is standard, with gradual return under physiotherapy guidance and technique modification.
• Surgical management: distal clavicle excision (resection arthroplasty) is the accepted operative treatment when non-operative care fails. Both open and arthroscopic techniques are described and yield comparable outcomes. The recommended resection is 5 to 10 mm of the distal clavicle, with preservation of the superior AC ligament and capsule to prevent posterior clavicle instability.
• Iatrogenic osteolysis: subacromial osteolysis after hook plate fixation is a recognised complication. Early plate removal (typically 3 to 6 months after implantation) is recommended to prevent this. Hardware removal is the first step; distal clavicle excision is reserved for persistent symptoms.
• Emerging therapies: platelet-rich plasma and other biologic injections have been reported in case series and small studies, but high-quality evidence is lacking and these are not yet standard of care.