The extensor retinaculum has a characteristic appearance on sonography. A hypoechoic appearance from anisotropy should not be confused with tenosynovitis.
Sonography of the musculoskeletal system is a useful diagnostic technique, but awareness and understanding of the pitfalls will minimize errors in diagnosis.
Objective. In our clinical practice, we have noted a caliber change of the posterior interosseous nerve (PIN) at the elbow as seen in the long axis on sonography simulating nerve entrapment. The objective of this study was to characterize the PIN using sonography in asymptomatic individuals. Methods. Our study retrospectively characterized the PIN in 50 elbows of 47 asymptomatic patients with sonography. Measurements of the PIN in a short‐axis cross section using the circumferential trace technique and the anteroposterior (AP) dimension in the long axis were made proximal, at, and distal to the arcade of Frohse. Results. There was reduction of the AP dimension of the PIN distal to the arcade of Frohse when compared with the measurements at the arcade of Frohse and proximal to the arcade (P < .0001); however, there was no significant difference between the cross‐sectional area of the PIN at all 3 levels (P = .59). Conclusions. The PIN normally flattens as it enters into the supinator muscle without a notable change in the cross‐sectional area. This appearance should not be misinterpreted as nerve entrapment when imaged in the long axis.
Anatomic variations in the anterior aspect of the shoulder, such as an accessory head of the biceps brachii muscle, are not uncommon. The magnetic resonance imaging and arthroscopic appearance of the accessory head of the biceps brachii has been recently described. This series demonstrates the sonographic appearance of the accessory head of the biceps brachii in the bicipital groove. It is an asymptomatic, flat, echogenic structure with average measurements of 7.7 × 1.2 mm in cross section. Knowledge of this anatomic variant can avoid the misdiagnosis of a longitudinal split tear and improve the accuracy of sonography.
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