Table of Contents
- 01. Rotator Cuff
- 1. Anatomy and Function
- 2. Pathogenesis
- 3. Terminology
- 4. Natural History
- 5. Ultrasound Technique
- 6. Spectrum of Findings
- 7. Ultrasound Pitfalls
- 8. References
- 02. Postoperative Rotator Cuff
- 03. Long Head of Biceps Brachii Tendon
- 04. Bursae
- 05. Joint Spaces
- 1. Acromioclavicular Joint
- 2. Glenohumeral Joint
- 3. Sternoclavicular Joint
- 4. Scapulothoracic
- 5. References
- 06. Fractures
- 07. Os acromiale
- 08. Adhesive Capsulitis
- 09. Deltoid
- 10. Pectoralis Major
- 11. Web Exclusive: Sternocostal Joints
6.3. Rotator Cuff Ultrasound: Partial-Thickness Tears
Partial-thickness tears are defined as a disruption of tendon fibers that does not allow communication between the glenohumeral joint cavity and the subacromial-subdeltoid bursa. Partial tears may be intrasubstance, or extend to either the bursal or articular surfaces of the tendon (figure 1-39). Articular surface partial-thickness tears most commonly affect the anterior aspect of the critical zone of the supraspinatus and are more prevalent than intrasubstance and bursal surface tears. Theoretical basis for the increased frequency of articular surface tears include peculiar histological and biomechanical properties. The bursal side layers are primarily composed of tendon bundles, which are resistant to rupture and may elongate under tensile load, whereas articular side layers are composed of a complex of tendon fibers, ligaments, and joint capsule, which is more susceptible to tear.176
US is as accurate as MRI to detect partial-thickness tears. In addition, although MR arthrography is currently considered the gold standard for imaging diagnosis, US may be most cost-effective because of its lower cost.177 Management of partial-thickness tears is conservative and surgery typically reserved for refractory symptoms.178
Articular Surface Partial-Thickness Tears
An articular surface partial-thickness tear typically appears as a mixed hyper-hypoechoic defect of the tendon adjacent to the greater tuberosity (figure 1-40). The bursal surface remains intact and shows normal convexity because there is no global volume loss. The terms rim-rent and PASTA (Partial Articular surface Supraspinatus Tendon Avulsion) are commonly used to describe these lesions. As previously mentioned, erosive calcific tendinopathy may simulate rim-rent tears and should always be included in the differential diagnosis (see figure 1-37). Another important differential diagnosis is anisotropy, as both conditions tend to affect articular surface fibers. However, hypoechogenicity caused by anisotropy is artifactual and can be differentiated from a true abnormality because it produces a more homogeneous hypoechoic appearance that can be minimized when the insonating beam is perpendicular to the tendon fibers (figure 1-41). The finding of a cortical irregularity adjacent to the hypoechoic focus is also helpful for differentiation purposes since it is a sensitive sign of an articular surface partial-thickness tear that is not found in anisotropy (video 1-10). These cortical irregularities are believed to result from muscle traction or exposure of the bone previously protected by tendon fibers to the synovial fluid.179 When a focal hypoechoic or anechoic tendon abnormality is seen adjacent to a cortical irregularity, it is important to determine whether the defect communicates with the glenohumeral joint space, representing an articular-surface tear, or is only in contact with the greater tuberosity, representing an intrasubstance tear. Doppler evaluation typically reveals increased vascularity as a normal reparative response to recent small tears, though it is usually unremarkable in chronic or larger tears (figure 1-42).156
Articular surface partial-thickness tears affecting the subscapularis, infraspinatus (figure 1-43), and teres minor tendons are relatively rare when compared to supraspinatus tears. Partial tears of the subscapularis tendon are mostly traumatic, while tears of the supraspinatus (video 1-11) and infraspinatus are usually degenerative. Articular surface partial-thickness tears of the infraspinatus have also been described in the setting of internal impingement (see section 2.1.3). In such cases, a labral tear is commonly associated and should be specifically addressed by MRI or MR arthrography. In the posterior aspect of the humerus, care should be taken not to confuse the normal bare area devoid of cartilage with a cortical irregularity secondary to a tear of infraspinatus or teres minor tendons (see figure 6-5).
Bursal Surface Partial-Thickness Tears
Because of the superficial location, tendon thinning and volume loss are typical features of bursal surface partial-thickness tears. At US, these tears are depicted as flattening of the bursal surface and loss of convexity of the affected tendon (figure 1-44; video 1-12). These findings are more conspicuous when there is simultaneous fluid distension of the subacromial-subdeltoid bursa (figure 1-45). Dynamic evaluation during graded compression (video 1-13) and both internal and external rotation of the shoulder should be liberally used to differentiate a bursal surface partial-thickness tear from the commoner full-thickness tear (figure 1-46). Some bursal surface tears may extend to the greater tuberosity, but are still considered a partial-thickness tear as long as the articular surface tendon fibers remain intact. In such cases, cortical irregularities very similar to those observed in articular surface tears may result from chronic exposure of the bone to the synovial fluid present in subacromial-subdeltoid bursa.
Figure 1-44. Bursal surface partial-thickness tear of the supraspinatus tendon.
Intrasubstance Partial-Thickness Tears
Intrasubstance partial tears do not communicate with neither the subacromial-subdeltoid bursa nor the glenohumeral joint. These tears may be located within the tendon substance (figure 1-47) or in contact with the greater tuberosity (figure 1-48). In the latter situation, cortical irregularities secondary to muscle traction are often seen, but volume loss and flattening of the bursal surface of the affected tendon are not typical. Isolated intrasubstance tears not affecting the supraspinatus tendon are exceedingly rare (video 1-14). On a microscopic level, tendon degeneration is characterized by microtears that coalesce to form macroscopic tears, and it may be difficult to arbitrarily differentiate intrasubstance partial-thickness tears from severe tendinopathy.
6.3.1. Grading of Partial-Thickness Tears
Grading of partial-thickness tears is much like debating over the war on terror: (1) we know we have a problem, (2) we do not have a consensual solution, (3) everyone has an opinion, and (4) we can make the situation worse. Although different classification schemes are described,180-183 we consider practical to describe only the vertical component of the tear relative to tendon thickness as greater, equal, or lesser than 50%. On daily basis, we describe tears in the 40-60% range as 50%. The horizontal component of a tear has not received much attention from orthopaedic surgeons and its description is considered optional.40,150,184,185 In order not to make the situation worse, the vertical component should not be expressed in absolute terms using submillimetric scale nor in relative terms using fractions of percentage because both situations create an artificial environment for comparison in follow-up (figure 1-49). The reason we choose 50% as a cut-off value refers to surgical planning: debridement is usually undertaken if bursal- or articular-surface tears involve less than 50% of tendon thickness, while repair is generally indicated for larger lesions.186 Evidence to support this approach comes from a cadaveric study that demonstrated consistent increases in supraspinatus strain with articular surface tears involving 50% and 75% of tendon thickness, but not 25%.188 In the same study, tendon repair returned supraspinatus strain almost to the intact levels.187 A partial-thickness tear that involves more than 50% of tendon thickness may be compressible and simulate a full-thickness tear. However, misdiagnosing a high-grade partial-thickness tear for a small full-thickness tear is not clinically relevant because they are often treated as if they were a full-thickness tear.188
6.3.2 Follow-up of Partial-Thickness Tears
Partial-thickness tears are permanent lesions that do not disappear after successful treatment. Follow-up studies are best reserved for clinically refractory patients at risk for tear progression and should be avoided in the absence of symptoms because informing patient that he still has a lesion may cause symptoms to recur (figure 1-50).