Tendon Thickness and Depth from Skin for Supraspinatus, Common Wrist and Finger Extensors, Patellar and Achilles Tendons: Ultrasonography study of healthy subjects

Abstract

Summary Objective To assess normal intervals for depth from skin surface to tendon and tendon thickness, and their variance by demographic factors. Methods A standardised ultrasound imaging procedure was performed by a trained physiotherapist. The procedure included bilateral assessment of tendon thickness and depth to tendons and a blinded analysis of reliability. Regression analysis was used to correlate demographic variables with tendon thickness and depth. Material A sample of 448 tendons including the supraspinatus, common extensor digitorum and carpi, distal patellar and Achilles tendons was examined. The material was stratified by sex, body mass index, age, manual/non-manual work and sports participation. Results Evaluation of tendon thickness and depth from skin surface could be performed with high intra-observer reliability in the test-retest situation. Depth measurements had a mean test-retest difference of 0.24 mm (95% limits of agreement ± 0.37 mm), while mean test-retest difference tendon thickness was 0.22 mm (95% limits of agreement ± 0.35 mm) using the method advocated by Bland and Altman (1986) . The average depth to the supraspinatus tendon was 9.6 mm, but depth increased with body mass index and was doubled in overweight white-collar workers. In the hand-in-back position, depth to the supraspinatus tendon was reduced by 1.1 mm to 8.5 mm. Other mean depth scores were 1.2, 1.6 and 3.1 mm for the common extensors, Achilles and patellar tendons respectively. Mean tendon thickness was 6.6 mm for the supraspinatus tendons, 1.5 mm for the common extensor tendons, 5.8 mm for the patellar tendons and 5.5 mm for the Achilles tendons. Conclusion Depth from skin surface to superficially located tendons does not seem to depend on demographic variables. For the supraspinatus tendon, body mass index is moderately correlated to depth. Tendon thickness varies with anatomic location and between subjects, but individual differences between sides are small.