Tendons

Although sonography and MRI are often complementary in diagnosing pathologic conditions, the spatial resolution of sonography is superior to that of MRI for defining the fine internal fibrillar structure of large tendons [34,35]. The typical sonographic appearance of a tendon is that of a parallel series of hyperechoic lines separated by less echogenic lines [32]. An exception to this is at a tendon insertion, where the tendon often has a hypoechoic appearance that should not be misinterpreted as a tear. This appearance is caused by an-isotropy, in which collagen fibers that are not parallel to the ultrasound transducer do not reflect back the sound waves. Sonography also allows dynamic assessment of tendon subluxation and function.

Quadriceps tendon

When evaluating this tendon, it is important to scan all four components in both the short and long axes from the muscle-tendon junction to the point of insertion. Visualization of this tendon and its pathology are well-delineated using sonography (Fig. 9). Dynamic visualization of the tendon performed by using ultrasound while moving the knee also provides better evaluation of a tendon tear. Flexion can improve demonstration of a tear by causing the torn ends of the tendon to pull apart. As a result, what may appear to be a partial-thickness tear in extension is seen to represent a complete tear in flexion. Accompanying chronic thickening of the tendon and hematoma can also be evaluated with sonography. Tendinopathy of the quadriceps tendon associated with sports such as weight lifting and basketball appears on sonography as a diffuse hypoechoic swelling of the tendon [34].

Tendinopathy Quad Tendon

Fig. 9. Tendinopathy of the quadriceps tendon. (A) Longitudinal sonographic image of the distal quadriceps tendon demonstrates a hypoechoic (arrow) area just proximal to the insertion onto the patella (notched arrow). (B) Color Doppler image, same as (A), shows areas of increase flow within the tendon. (C) Transverse image better depicts the abnormal hypoechoic areas and expansion of the quadriceps tendon (arrows), with marked hypervascularity (D) consistent with severe insertional tendinopathy.

Fig. 9. Tendinopathy of the quadriceps tendon. (A) Longitudinal sonographic image of the distal quadriceps tendon demonstrates a hypoechoic (arrow) area just proximal to the insertion onto the patella (notched arrow). (B) Color Doppler image, same as (A), shows areas of increase flow within the tendon. (C) Transverse image better depicts the abnormal hypoechoic areas and expansion of the quadriceps tendon (arrows), with marked hypervascularity (D) consistent with severe insertional tendinopathy.

Patellar tendon

Sonography is useful in the assessment of abnormalities of the patellar tendon and it attachments. Partial and complete tears of the patellar tendon can be assessed sonographically, with similar findings on sonography as described for the quadriceps tendon. 'Jumper's knee'' at sonography is visualized as a thickened proximal patellar tendon. Tendinopathy by sonography is seen as hypoechoic swelling of the tendon (Fig. 10). Small, focal, partial tears (Fig. 11), calcification, or dystrophic ossification can be visualized within the patellar tendon [36]. The sonographic findings of Osgood-Schlatter disease include swelling around the unossified cartilage, fragmentation of the ossification center with reduced internal echogenicity, thickening of the tendon, and infrapatellar bur-sitis [34,36].

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