Acromioclavicular junction injury-MRI

27 years old male presence with sports injury to the right shoulder. The MR shows disruption of superior and inferior acromioclavicular ligaments with horizontal instability of the joint with marrow edema including the articular margins along with trapezoid component of the coracoclavicular ligament edema suggesting type II / III variety. Case submitted by Dr MGK Murthy and Mr Hari Om.

Teaching Points :

• AC joint functions primarily to transmit the weight bearing from axial skeleton to appendicular skeleton with small rotatory movement possible (5 to 20 degrees in various studies).

• Usually occur in contact sports with shoulder and the body falling over the joint in falls on out stretched hand.

• Rockwood classification has 6 types depending of the severity, with type I and II responsible for horizontal instability (anteroposterior) due to superior and inferior acromioclavicular ligament injuries.

• Type III to VI also include vertical in stability due to additional coracoclavicular ligament injury.

• CC ligament has triangular medial component (conoid) and quadrilateral trapezoid component (lateral) with conoid being responsible for anterosuperior stability and the later for posterior stability.

• Usually type I, II and occasionally type III can be managed conservatively, with other types offen requiring surgical procedures.

• Removal of the coracoclavicular screw after some time is needed to permit rotatory movement.