Distal Clavicle Osteolysis

Osteolysis of the distal clavicle is an uncommon condition that can occur from AC joint overload or less commonly from direct trauma. 
== Anatomy ==
The clavicle is an S-shaped bone. The medial growth plate fuses late in ones early 20s. The AC joint is a diarthrodial joint with a fibrocartilage meniscus. The ligamentous restraints are the AC ligaments for horizontal stability and CC ligaments for vertical stability.
== Epidemiology ==
It classically affects young mostly male weightlifters or other athletes that regularly perform heavy bench presses or military presses over a long period of time. It can also affect any overhead athletes such as tennis players, swimmers, or occupational workers that do a lot of overhead activities.
It is bilateral in around 20% of cases.Flores DV, Goes PK, Gómez CM, Umpire DF, Pathria MN. Imaging of the Acromioclavicular Joint: Anatomy, Function, Pathologic Features, and Treatment. Radiographics. 2020 Sep-Oct;40(5):1355-1382. doi: 10.1148/rg.2020200039. Epub 2020 Aug 7. PMID: 32762593.
== Pathophysiology ==
It is caused by repetitive stress and micro-fracture leading to osteopenia.
There are two distinct forms but they have identical histopathologic and imaging findingsRoedl JB, Nevalainen M, Gonzalez FM, Dodson CC, Morrison WB, Zoga AC. Frequency, imaging findings, risk factors, and long-term sequelae of distal clavicular osteolysis in young patients. Skeletal Radiol. 2015 May;44(5):659-66. doi: 10.1007/s00256-014-2092-2. Epub 2015 Jan 7. PMID: 25560997.
* Post-traumatic: occuring weeks to months after injury
* Atraumatic: stress-induced overload seen in overhead athletes (weight lifters especially) and labourers.
However erosions can be seen in a wide range of conditionsGaillard, F., Baba, Y. Distal clavicular erosion (differential). Reference article, Radiopaedia.org. (accessed on 06 Mar 2022) https://doi.org/10.53347/rID-1231
===== Bilateral erosions =====
* atraumatic distal clavicular osteolysis: due to repetitive microtrauma; classically described in weightlifters, but can affect anyone performing repetitive overhead lifting and carrying.
* hyperparathyroidism
** subchondral bone resorption; usually symmetric with osteopenia, abnormal trabecular pattern
** the acromion is normal, but the sternoclavicular joint may be affected
* rheumatoid arthritis
** bilateral or unilateral changes with soft tissue swelling, subchondral osteoporosis and erosion of the outer third of the clavicle
** acromial erosions may occur later in the disease process
* scleroderma
* psoriatic arthropathy
* cleidocranial dysostosis
* pyknodysostosis (rare)
* progeria (rare)
===== Unilateral erosion =====
* rheumatoid arthritis
* post-traumatic distal clavicular osteolysis
* myeloma
* metastases
* osteomyelitis
A useful mnemonic is SHIRT Pocket for Scleroderma, Hyperparathyroidism, Infection (osteomyelitis), Rheumatoid arthritis, Trauma, Progeria.
== Clinical Features ==
It presents similarly to AC joint osteoarthritis. Pain is provoked by repetitive loading (e.g. bench press or push-ups). There is tenderness over the distal clavicle and AC joint. Provocative ACJ tests may cause pain (cross body adduction test, AC shear testing, active compression test). 
== Imaging ==
Plain films: AP and Zanca views (15 degree cephalad tilt). This may be normal in early disease. Look for radiographic evidence of osteolysis. Early findings are bone loss or subchondral cyst formation at the distal clavicle. In more severe disease there is focal osteoporosis, loss of bone detail, AC joint widening, and more severe cystic change. In extreme cases the entire distal third of the clavicle shows signs of bone resorption. ACJ osteoarthritis is common.
MRI: bone marrow oedema with increased signal on T2 sequences. The distal clavicle is involved more than the acromion. There may be subchondral cystic change, subchondral fracture, and distal clavicle periostitis. The ACJ may have an effusion and capsular oedema.
== Treatment ==
First line treatment is rest from aggravating activities and NSAIDs.
Change technique such as scapular retraction and keeping the grip on the bench press to be below 1.5 times the biacromial distance (ACJ to ACJ joint) to reduce stress on the AC joint. The patient should end descent of the weight 4-6cm above the chest.
A corticosteroid injection may be a temporising measure if the athlete refuses to rest due to being in-season.
Resection of the distal clavicle is reserved for refractory cases.
== References ==
Category:Shoulder Conditions