CHAPTER 2: Imaging the Shoulder

1. INTRODUCTION: FAST SHOULDER FACTS

❑ Why Is the Shoulder So Frequently Injured?

The ball-and-socket form of the shoulder joint possesses great range of motion but is combined with little bony stability and mechanical protection. Thus the shoulder is susceptible to a variety of soft tissue and cartilaginous injuries, fractures, and dislocations.

❑ Traumatic Injuries

• Falls—the most common mechanism of injury is a fall on an outstretched hand.

  • ◗ In an elderly osteoporotic female, this typically results in a fracture of the surgical neck of the humerus.

  • ◗ In the younger adult, fractures typically occur from higher energy trauma, as in falls, from motor vehicle accidents, or during athletic activities. Fractures of the humeral head may be associated with dislocation of the glenohumeral joint or injury to the rotator cuff muscles.

• Rotator Cuff Tear—the most common tear involves the hypovascular critical zone of the supraspinatus tendon, 1 cm proximal to its insertion on the greater tuberosity.

• Impingement Syndrome—two types of impingement occur when the arm is overhead.

  • ◗ External impingement compresses the rotator cuff in the supraspinatus outlet.

  • ◗ Internal impingement compresses the posterior capsule and rotator cuff between the humeral head and the glenoid.

• Dislocations at the Glenohumeral Joint—95% of dislocations are anterior, meaning that the humeral head dislocates anterior to the glenoid fossa. Associated injuries include the Hill-Sachs lesion, a compression fracture of the posterolateral humeral head sustained during the dislocation, and the Bankart lesion, a detachment of the labrum from the anterior glenoid rim. A Bankart fracture exists if there is a bony avulsion of the glenoid rim.

• Acromioclavicular Joint Separations—“shoulder separation” refers to a ligamentous sprain or rupture at the acromioclavicular (AC) joint. The degree of instability is determined by evaluating the coracoclavicular and acromioclavicular distances in anteroposterior (AP) stress radiographs.

❑ The Imaging Choices

• Radiographs are the initial study for all shoulder problems. Radiographs adequately demonstrate most fractures, dislocations, and calcific tendinitis, as well as nontraumatic disorders such as the various arthritides.

• Computed tomography (CT) provides optimal visualization of complex fractures, especially in characterizing fracture/dislocations of the humeral head. CT assists in treatment planning for complex fractures of the proximal humerus.

• Magnetic resonance imaging (MRI) is used to evaluate glenoid labrum tears, rotator cuff tears, impingement syndromes, instability, and tendon and bursa abnormalities. The shoulder is the most frequently performed MRI examination because of the frequency of soft tissue injuries at the shoulder clearly defined by MRI.

• Musculoskeletal ultrasound (MSUS) is equivalent to MRI in the evaluation of bursitis, long head of the biceps tenosynovitis, and re-tears of prior surgical rotator cuff repairs. It is superior to MRI in the evaluation of rotator cuff tears after total shoulder arthroplasty. MSUS may be used instead of MRI in the initial evaluation of rotator cuff tears in general. MSUS is ...