Description

The acromioclavicular (AC) joint is the articulation between the acromion process of the scapula and the lateral end of the clavicle. It is one of the important functional joints that allows a full range of movement at the glenohumeral joint. A joint capsule and several ligaments hold the joint in situ, assisted by the trapezoid and conoid coracoclavicular (CC) ligaments that connect the coracoid process of the scapula to the mid/lateral clavicle.

Epidemiology

It is difficult to know how common such injuries are since there are no reliable population data; however, they seem to be highly prevalent among players of high-impact contact sports.¹ One series found that 41% of collegiate American football players had suffered AC injury.² Forty-five per cent of first class rugby players gave a history of suffering AC disruption, although functional outcome in the long-term appeared to be good in this group.³

Causes of shoulder pain⁴

Shoulder pain is a common symptom. Causes include:

• Rotator cuff pathology
• Bursitis
• Biceps tendonitis
• Labral tears
• Joint pathology, e.g. acromioclavicular, sternoclavicular and scapulothoracic

There are two broad causes of acromioclavicular joint problems:

1. AC joint disruption - when trauma leads to varying degrees of displacement of the distal clavicle from the local ligaments and muscles
2. Osteoarthritis (OA) and/or osteolysis of the AC joint

Acromioclavicular joint disruption

Mechanism of injury

This usually follows trauma, e.g. due to a direct blow to the acromion with the humerus adducted, as in collision in high-impact contact sports, or after a fall on to the apex of the shoulder. Injury may occur as a consequence of throwing sports or chronic irritation due to activities that require repetitive overhead motions, particularly weight lifting. Its aetiology is uncertain but may be due to repeated stress fractures of the lateral clavicle.

Osteoarthritis and distal clavicular osteolysis

• OA of the AC joint may occur after injury, repetitive overuse or, more rarely, as a primary phenomenon.⁵
• Distal clavicular osteolysis may occur spontaneously in rheumatoid arthritis, hyperparathyroidism, myeloma, systemic sclerosis, due to infection and in those who are involved in throwing sports/extensive upper limb weight training.

Clinical symptoms and signs

AC joint disruption

• There will usually be a history of relevant trauma and severe pain over the lateral shoulder.
• There may be marked tenderness of the AC joint and a visible/palpable 'step' if there is clavicular separation. This is best viewed with the arm adducted across the body.
• The position of the clavicle should be determined along its whole length (associated sternoclavicular abnormalities may occur as well as fracture of clavicle).
• Brachial and radial pulses should be checked along with sensory and motor function in the affected arm due to the possibility of injury to brachial plexus and axillary/subclavian vessels.
• Patients may also present with acute complications of AC joint disruption. For example:
  • Injury to axillary/subclavian vessels
  • Injury to brachial plexus
  • Muscular avulsion, particularly deltoid and trapezius
  • Rarely pneumothorax if associated clavicular fracture

OA and distal clavicular osteolysis

• Diffuse lateral shoulder pain and/or localised AC joint pain.
• May be simply an ache in deltoid area.
• Often worse at night.
• Local tenderness with exacerbation on passive and active shoulder movements.
• Cross-adduction (i.e. reach over front of opposite shoulder) often worsens pain and further passive cross-adduction by examiner may aggravate this.⁵
• Reduced range of movement is rare unless there is a prolonged period of arthritis.

Differential diagnosis

• Clavicular fracture
• Shoulder (glenohumeral) dislocation
• Cervical spine fracture
• Bursitis (especially in cases of OA and osteolysis)
• Tendonitis (especially in cases of OA and osteolysis)
• Other causes of shoulder pain (see Causes above)

Diagnostic imaging

• Plain radiographs are the initial choice.
• Type I and II injuries may be differentiated using stressed radiographs where weights are hung from the patient's wrists, although many consider this technique to be unhelpful.
• A Zanca view (AP view where beam is directed at the AC joint with 10º cephalic tilt) optimises the view of the joint.
• CXR and full clavicle views may be needed in some cases.
• Carefully inspect scapula to rule out associated scapular fracture.
• A variety of images may be required to assess the degree of AC joint disruption.

Management

AC joint disruption

• Types I and II injuries are managed conservatively with ice, a sling for 1-3 weeks and non-steroidal anti-inflammatory drugs (NSAIDs) followed by physiotherapy to strengthen muscles and ligaments after the acute phase.
• Type III injuries should be managed conservatively but carefully selected cases may benefit from surgical intervention if conservative therapy fails.⁶
• Types IV to VI are nearly always treated with open reduction and internal fixation.
• All acute lesions thought to be worse than type II should be referred urgently for an orthopaedic opinion.

OA/osteolysis

• Activity modification, physiotherapy and NSAIDs/other analgesia.
• Intra-articular corticosteroids may provide relief of symptoms for up to 3 months in expert hands. Currently there is no consensus in terms of dosage, and injections should be limited to fewer than 4 per year.⁷ Duration of analgesia is very variable with ranges of 2 hours to 3 months reported.
• In severe cases of OA or osteolysis, distal clavicular resection may need to be considered. This can be performed openly or arthroscopically.⁸
• In OA, consider surgery for severe cases where there is failure of response to conservative management after 6 months; however, various factors need to be considered.⁹

Late complications

• Impingement syndrome of supraspinatus tendon due to narrowing of scapular outlet
• OA of AC joint
• Frozen shoulder and chronic shoulder pain/limitation of movement¹⁰

Document references

1. Simovitch R, Sanders B, Ozbaydar M, et al; Acromioclavicular joint injuries: diagnosis and management. J Am Acad Orthop Surg. 2009 Apr;17(4):207-19. [abstract]
2. Kaplan LD, Flanigan DC, Norwig J, et al; Prevalence and variance of shoulder injuries in elite collegiate football players. Am J Sports Med. 2005 Aug;33(8):1142-6. Epub 2005 Jul 7. [abstract]
3. Webb J, Bannister G; Acromioclavicular disruption in first class rugby players. Br J Sports Med. 1992 Dec;26(4):247-8. [abstract]
4. Buttaci CJ, Stitik TP, Yonclas PP, et al; Osteoarthritis of the acromioclavicular joint: a review of anatomy, biomechanics, diagnosis, and treatment. Am J Phys Med Rehabil. 2004 Oct;83(10):791-7. [abstract]
5. Quillen DM, Wuchner M, Hatch RL; Acute shoulder injuries. Am Fam Physician. 2004 Nov 15;70(10):1947-54. [abstract]
6. Mignani G, Rotini R, Olmi R, et al; The surgical treatment of Rockwood grade III acromioclavicular dislocations. Chir Organi Mov. 2002 Jul-Sep;87(3):153-61. [abstract]
7. Skedros JG, Hunt KJ, Pitts TC; Variations in corticosteroid/anesthetic injections for painful shoulder conditions: comparisons among orthopaedic surgeons, rheumatologists, and physical medicine and primary-care physicians. BMC Musculoskelet Disord. 2007 Jul 6;8:63. [abstract]
8. Rabalais RD, McCarty E; Surgical treatment of symptomatic acromioclavicular joint problems: a systematic review. Clin Orthop Relat Res. 2007 Feb;455:30-7. [abstract]
9. Docimo S Jr, Kornitsky D, Futterman B, et al; Surgical treatment for acromioclavicular joint osteoarthritis: patient selection, surgical options, complications, and outcome. Curr Rev Musculoskelet Med. 2008 Jun;1(2):154-60. [abstract]
10. Wheeless Orthopaedic Online Textbook Duke University Medical Center's Division of Orthopaedic Surgery, Acromioclavicular Joint

Acknowledgements