Ultrasound examination of the achilles tendon
There is growing evidence that the clinical and operative use of ultrasound imaging can benefit patients with Achilles tendon pathology. Although ultrasonography has been stigmatized as too operator dependent and necessitating a steep learning curve, it has been our experience that the modality is relatively straightforward. Surgeons are in a unique position to utilize this technology, as they have the firm grasp of anatomy that is essential to the interpretation of sonograms. Ultrasound provides real-time dynamic imaging in the office and in the operative setting that directly benefits our patients. Ultrasound images can assist the clinician in determining the exact pathologic process, including location of symptoms, assessment of concurrent pathology, response to treatment, and the planning and intraoperative assessment of tendinous pathology. The Achilles tendon is the largest superficially located tendon of the body and is ideally suited to ultrasound examination. Achilles tendon morphology is best visualized with a high-frequency linear transducer (5 to 10 MHz). After an appropriate history and physical is obtained, the patient is positioned prone with both lower extremities disrobed (Fig. 2.1). As with all tendons, images of the Achilles tendon should be obtained in two orthogonal planes. Longitudinal and transverse images should be obtained from the musculotendinous junction to the distal tendon insertion on the calcaneus. To obtain an orderly and reproducible examination, imaging begins directly over the area of pain or tenderness with the foot in the gravity neutral position. In general, transverse imaging is followed by longitudinal imaging. Because ultrasound is a dynamic imaging modality, movie clips of the examination can be saved in the patient's electronic record. After the static examination of the area of interest, the surgeon grasps the patient's foot, introducing passive dorsiflexion and plantarflexion. This is followed by visualization of the symptomatic area with active range of motion. Finally, a full examination of the tendon from its most distal insertion proximally to the myotendinous junction is performed. Obviously, examination may be extended to the gastrocnemius and soleus muscles, depending on the clinical situation. The normal Achilles tendon, as shown in Figure 2.2, appears echogenic (bright) with an organized fibrillar ultrastructure. The paratenon envelops the tendon as a thin, echogenic tissue layer clearly distinct from the tendon under dynamic imaging. The sural nerve and accompanying lesser saphenous vein course from medial to lateral and proximally to distally along the tendon. The plantaris tendon runs along the medial side of the tendon distally. Deep to the Achilles tendon lies the bipennate muscle belly of the flexor hallucis longus. In most cases, a diagnosis can be made based on the two-dimensional (2D) real-time appearance of the tendon; an acutely ruptured Achilles tendon is clearly identified by a discontinuity of collagen fibrils separated by hypoechoic hematoma (Fig. 2.3). Chronic ruptures demonstrate attenuation of the tendon and echogenic fat herniating into the defect (Fig. 2.4). The calcification and tendinosis pathognomonic of insertional disease can be easily correlated with physical examination findings (Fig. 2.5). In insertional disease, the examiner may use the transducer to palpate and image the osseotendinous junction simultaneously. It should be stressed that all findings must be confirmed in two planes. © Springer Science+Business Media, LLC 2009.
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