Imaging for Rotator Cuff Pathology

It is our preference to obtain initial radiographs on all patients with concern for rotator cuff pathology due to the ease with which these images are acquired, the relative low cost of this modality, and the ability to evaluate for other conditions, such as arthritis or evidence of previous trauma or surgical interventions.

A complete radiographic evaluation of the shoulder, when concerned about potential rotator cuff pathology, includes anteroposterior (AP), Grashey, supraspinatus outlet, and axillary lateral views ( Fig. 6.1 ). We will also add an AP active-abduction view when we have suspicion of large rotator cuff tears or concerns with advanced shoulder osteoarthritis.

The Grashey view is a true AP of the glenohumeral joint and is obtained with the patient rotated posteriorly 35–45 degrees so that the plane of the scapula is parallel to the imaging cassette.

The axillary lateral image provides an orthogonal image to evaluate the condition of the glenoid, humeral head, and acromion.

The supraspinatus outlet view shows acromion morphology, which is classified according to Bigliani.

The AP active-abduction image is obtained with the patient holding a 1–2 lb weight in 45 degrees of abduction to better evaluate for humeral head migration and joint space narrowing. Patients with anterior-superior escape or dynamic instability will show very clear superior migration of the humeral head on this view ( Fig. 6.2 ).

The acromiohumeral interval (AHI) can be measured ( Fig. 6.3 ). An AHI less than 7 mm is associated with rotator cuff pathology. In one cohort of patients, for patients with an AHI less than 7 mm, 90% had a supraspinatus tear, 67% had an infraspinatus tear, and 43% had subscapularis tears.

An increased critical shoulder angle, defined as a combined measurement between the glenoid inclination and lateral extension of the acromion, has been associated with rotator cuff pathology ( Fig. 6.4 ). Conversely, a decreased critical shoulder angle was associated with primary glenohumeral osteoarthritis. A group of asymptomatic patients had a critical shoulder angle of 33.1 degrees, while for those with rotator cuff tears it was 38.0 degrees and for those with glenohumeral arthritis it was 28.1 degrees.

The acromion shape may have an association with presence of a rotator cuff tear. In one retrospective analysis, 88.9% of patients with a type 3 acromion had an associated rotator cuff tear.

Patients with calcific tendonitis, which is visible on radiographs, may present with symptoms similar to impingement syndrome or rotator cuff pathology ( Fig. 6.5 ).

Chronic bony changes may be apparent in the setting of a chronic massive rotator cuff tear. The humeral head begins to undergo changes described as femoralization. The acromion also shows evidence of remodeling, known as acetabularization ( Fig. 6.3 ).

An os acromiale ( Fig. 6.6 ), which is a failure of fusion of one of the ossification centers of the acromion, is best seen on an axillary lateral radiograph. This finding has been associated with rotator cuff pathology.

In the setting of an acute traumatic injury, a radiographic evaluation will diagnose a proximal humerus fracture. An isolated greater tuberosity fracture may appear similar clinically to a patient with an acute rotator cuff injury ( Fig. 6.6 ).

Plain radiographs are relatively inexpensive and usually easy to obtain.

As part of an initial evaluation, radiographs can help exclude certain conditions that may present with symptoms that overlap with rotator cuff injuries, such as early osteoarthritis and calcific tendonitis.

Radiographs offer no soft tissue evaluation, so the information regarding the rotator cuff is limited with this imaging modality.

Most signs associated with rotator cuff pathology are present only in the chronic setting.

Sound waves of a certain frequency are generated from an ultrasound transducer and reflected back from the underlying structures to the ultrasound transducer to generate an image.

Musculoskeletal ultrasound wave frequency averages 5–12 MHz (range 4–17 MHz).

High-frequency sonographic waves are attenuated more quickly as they pass through tissue, meaning that higher-frequency ultrasound transducers have less imaging depth but the benefit of higher resolution capabilities.

Sound waves best create an image when they are oriented perpendicular to the collagen fibrils that make up the particular tissue or tendon being evaluated. This perpendicular orientation produces the characteristic bright reflective echo that is seen on ultrasound images. Deviation from the perpendicular results in an area of decreased echogenicity, possibly giving the false impression of tendon pathology. This concept is termed anisotropy .

• An example of anisotropy is seen in evaluating the biceps tendon in Fig. 6.7 .

  

The following parameters can be adjusted for better image quality:

• Depth of field of view

• Depth of focus

• Gain and time gain compensation (i.e., change in amplitude)

• Frequency of the probe

Convention for recording and viewing ultrasound images:

• The left side of the screen represents posterior and superior

• The right side of the screen represents anterior and inferior

• Always obtain orthogonal views of the structure of interest

• Label findings both in the long and short axes

Standard examination of the shoulder with ultrasound includes a systematic evaluation of the joint ( Table 6.1 ).

• The rotator cuff is usually examined starting with the long head of the biceps anteriorly and working from anterior to posterior, completing the exam with evaluation of teres minor.

• Each tendon should be evaluated in a short axis and long axis (i.e., orthogonal views).