The Health Flyer
The AC joint
What is the AC joint ?
The AC ( acromioclavicular ) joint is a synovial joint located at the top of the shoulder , where the lateral end of the clavicle articulates with the acromion of the
Neil Liffen scapula . The AC has a joint capsule ( fibrous layer ) with a synovial membrane , which secretes synovial joint fluid , and the joint includes an internal articular disc ( see Figure 1 ).
There are three major ligaments present in the acromioclavicular joint :
• Acromioclavicular
• Conoid
• Trapezoid
Collectively , the conoid and trapezoid ligaments are known as the coracoclavicular ligament . It is a very strong structure , effectively suspending the weight of the upper limb from the clavicle .
Common injuries
AC joint injuries are relatively common in young athletes . Most injuries occur during contact sports such as rugby ,
Figure 1 . ACJ anatomy
wrestling , and hockey , due to the pressure that these sports have on the shoulder joints .
The Rockwood classification ( 1998 ) is the most common classification system in use for AC joint injuries ( see Figure 2 ). The classification takes into account not only the AC joint but also the coracoclavicular ligament , the deltoid and trapezius muscles , and the direction of dislocation of the clavicle with respect to the acromion .
Figure 2 . Rockwood classification ACJ injuries
Below shows the types of injuries associated with the AC joint , as categorised by the Rockwood classification . Types IV , V , and VI are variants of type III :
• Type I : clavicle not elevated with respect to the acromion
• Type II : clavicle elevated but not above the superior border of the acromion
• Type III : clavicle elevated above the superior border of the acromion but coracoclavicular distance is less than twice normal ( i . e . < 25 mm )
• Type IV : clavicle displaced posteriorly into trapeziu
• Type V : clavicle is markedly elevated and coracoclavicular distance is more than double normal ( i . e . > 25 mm )
• Type VI : clavicle inferiorly displaced behind coracobrachialis and biceps tendon , which is rare
Source : https :// radiopaedia . org / articles / rockwood-classification-ofacromioclavicular-joint-injury
The study concluded that the average time lost to sport due to an AC joint injury was 18 days , with low-grade injuries averaging 10 days lost . Highgrade injuries averaged 64 days lost to sport , and 71 % elected to undergo surgical repair / reconstruction ( Pallis et al . 2012 .)
Figure 3 . Right side Type II ACJ injury as demonstrated on ultrasound
AC joint injuries can lead to degenerative changes in the joint later in life . At ECP we may use ultrasound to further characterise AC joint injuries to help the patients and our understanding and give a specific diagnosis ( see Figure 3 ).
About Neil Liffen
Neil Liffen currently spends his career combining his work as an Extended Scope Practitioner in Physiotherapy , with his work as a Musculoskeletal Diagnostic Sonographer . His work at East Coast Physio involves performing diagnostic ultrasound for several radiology departments based in NHS hospitals . He has vast experience in performing examination , scanning and treatment of musculoskeletal conditions .
If you would like further information or advice , please contact Neil on 01394 288444 or email : info @ eastcoastphysio . co . uk .
14 THE FLYER | JUNE 2018
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