[The Achilles tendon: echography at different frequencies. Comparative study].

: The authors report their experience with a comparative US study employing different-frequency probes (7.5, 10, 13 and 15 MHz) in Achilles tendon conditions. The study population included 49 patients, 37 of them athletes. All patients complained of the same symptoms: achillodynia in the middle third (group A, 29/49 cases), achillodynia in the lower end (group B, 16/49 cases), suspected partial rupture in the middle third (group C, 2/49 cases) and suspected distal rupture in the upper third (group D, 2/49 cases). In group A, the different frequencies yielded different results. 7.5 MHz frequencies yielded negative results in 13/29 patients, versus 3/29 with higher frequencies, which demonstrated peritenon inflammation in 10/29 cases. In the remaining 16 cases, where 7.5 MHz frequencies had shown tendon inflammation and degeneration, the higher frequencies confirmed the findings, even though their accuracy was greater. On the contrary, in the cases of distal achillodynia where pain was mainly due to inflammation of the retrocalcaneal bursa, the different frequencies yielded similar results, even though the higher ones proved more accurate in revealing tendon abnormalities--i.e., thickening, focal hypolucencies, spotty microcalcifications, irregularity of the bone lining. In group B, the different frequencies once again exhibited similar results showing a focal hypoechoic discontinuity which was correctly diagnosed on the basis of clinical history. Finally, as for group C, the lower frequencies gave better results because of the deeper location of the region of interest. In both cases a small blood collection was visible, between gastrocnemius and soleus, in the absence of clear-cut tendon lesions. No matter what the condition, the higher frequencies were extremely valuable since they allowed excellent demonstration of tendon anatomy. The tendon is enveloped by the peritenon, made of two macroscopically distinct sheaths the distinction of which is allowed by higher frequencies when a minimal amount of fluid is present. From the peritenon, the intratendon septa originate circumscribing spaces containing tendon fiber bundles. The vessels, which run longitudinally, are located within the confluence of the septa. On US images, the septa appear as thin hypoechoic stripes or small hyperechoic spots depending on the type of scan (longitudinal/axial). As to tendon fibers--i.e., tenocytes, collagen and elastic fibers--their pattern is homogeneous and hypoechoic since devoid of interfaces.