Measurement of the thickness of the common extensor tendon can be performed in different ways. In a study by Krogh et al. [23] two different techniques are described, and the intra- and inter-observer variation is excellent with both methods. Method 1, labeled “1-cm measure,” measures tendon thickness 1 cm distal from the insertion of the common extensor tendon (on top of the lateral epicondyle), perpendicular to the length of the tendon (Fig. 4.3a and c). Method 2, labeled “plateau measure,” measures tendon thickness at an anatomical landmark at the horizontal bony surface of the lateral epicondyle, which is referred to as “the plateau.” “The plateau” is a flat aspect of the capitellum of the lateral epicondyle located between the insertion of the tendon and the radio-humeral joint. Tendon thickness is measured from “the plateau” to the tendon surface perpendicular to the length of the tendon (Fig. 4.3b and c). Other authors have used similar methods for tendon thickness measurement [18, 25].

It has been shown to have a good sensitivity and specificity as a diagnostic tool for patients with LE [9, 47, 49]. The color Doppler activity is usually seen in an area limited proximally by the tip of the lateral epicondyle and distally by the humeroradial joint space. The outer border is the most superficial fibers, and the deep border is the bone (Fig. 4.1). There are several ways to assess Doppler activity, but as yet no consensus has been reached regarding which method to use. In newer studies [23, 39] color Doppler activity is graded in a new ranking scale from grade 0–4 (see Fig. 4.4). This modulation can be used both in scientific studies and in daily clinical work. The grading is estimated in a 0.5-cm longitudinal part of the tendon with the maximal Doppler activity (region of interest, ROI). The scale is as follows: Grade 0: no activity, grade 1: single vessel, grade 2: Doppler activity in less than 25 % of the region of interest, grade 3: Doppler activity in 25–50 % of the region of interest, and grade 4: Doppler activity in more than 50 % of the region of interest. Regarding color Doppler activity, the results showed an excellent correlation between the observers and an overall satisfactory agreement [23]. However, factors including probe position, probe pressure, and equipment settings including gain, wall filter, color priority, and pulse repetition frequencies can influence the outcome.

Several other methods for assessing Doppler activity have been suggested, e.g., as a binary outcome (negative/positive), where grade 0 and 1 would count as negative Doppler activity and grade 2 or more as positive Doppler activity. In ­conclusion, it is difficult to compare the results of Doppler activity across studies because of the use of various methods.

Bony spurs (enthesophytes) were initially described on conventional radiographs [3, 40]. Bony spurring is defined as a bony outgrowth arising at the insertional site of the common extensor tendon (see Fig. 4.5). The bony spurs are easily seen on US, and several ultrasonographic studies in patients with LE have dealt with the observation of bony spurs [5, 9, 26, 39, 46]. However, the clinical significance of bony spurs is unclear.