Background: Lateral epicondylitis (LE) most commonly affects the Extensor Carpi Radialis Brevis (ECRB) tendon and
patients are generally treated with injection therapy. For optimal positioning of the injection, as well as an estimation of
the surface area and content of the ECRB tendon to determine the volume of the injectable needed, it is important to
know the exact location of the ECRB in relation to the skin as well as the variation in tendon length and location. The
aim of this study was to determine the variation in location and size of the ECRB tendon in patients with LE.
Methods: An observational sonographic evaluation of the ECRB tendon was performed in 40 patients with LE. The
length of the ECRB tendon, distance from the cutis to the center of the ECRB tendon, the length of the osteotendinous
junction at the epicondyle and the distance from cutis to middle of the osteotendinous junction were measured.
Results: The average tendon length was 1.68cm (range 1.27-1.98; SD 0.177). Compared to women, the ECRB tendon
of men was on average 0.12cm longer. Overall, the average distance from cutis to the center of the ECRB was 0.75cm
(range 0.50-1.46cm; SD 0.210), the average length of the junction was 0.55cm (range 0.35-0.87; SD 0.130), and the
distance from cutis to middle of the osteotendinous junction was 0.73cm (range 0.40-1.25cm; SD 0.210).
Conclusion: The size and depth of the ECRB tendon in patients with LE is largely variable. While there are no studies
yet suggesting sono-guided injection to be superior to that of blind injection, the anatomic variability of this study
suggests that the accuracy of injection therapy for LE might be compromised when based solely on bony landmarks
and therefore not fully reliable. As a result, there is value in further studies exploring the accuracy of the ultrasound
guided injection techniques.
Level of evidence: IV