Sonographic evaluation of the size of achilles tendon: the effect of exercise and dominance of the ankle

Abstract

This study was undertaken to measure and compare the thickness and cross-sectional area of the Achilles tendon between frequent- and infrequent-exercise subjects, and between the dominant and nondominant ankles in an asymptomatic Chinese population. Interobserver variability in the measurement of the size of Achilles tendon was also evaluated. High-resolution ultrasound (US) examination of Achilles tendons was performed in 40 healthy subjects (20 who frequently exercised, had exercise at least 3 days per week and at least 2 h per session; and 20 who infrequently exercised); their age range was 19 to 25 years. The thickness and cross-sectional area of the Achilles tendons were measured in a transverse scan at the level of medial malleolus. For each subject, the Achilles tendons were measured by five operators to evaluate the interobserver variability in the measurements. The mean thickness and cross-sectional areas of the Achilles tendon in a healthy Chinese population are 5.23 mm² and 56.91 mm²², respectively. The mean thickness of the Achilles tendon of frequent-exercise subjects (dominant ankle 5.43 mm, nondominant ankle 5.38 mm) was significantly greater than that of infrequent-exercise subjects (dominant ankle 5.08 mm, nondominant ankle 5.04 mm) (p < 0.05). The cross-sectional area of the tendons was also larger in frequent-exercise subjects but, whereas a significant result was found in dominant ankles (frequent-exercise subjects 60.46 mm²², infrequent-exercise subjects 54.71 mm²²) (p < 0.05), this was not the case for the nondominant ankles (frequent-exercise subjects 57.09 mm²², infrequent-exercise subjects 55.4 mm²²) (p > 0.05). In both frequent- and infrequent-exercise subjects, there was no significant difference in the mean thickness and cross-sectional area of Achilles tendon between dominant and nondominant ankles (p > 0.05). There was a high reproducibility in the sonographic measurement of the thickness (68%) and cross-sectional area (81%) of Achilles tendons. Results suggested that exercise would cause increase in the thickness and cross-sectional area of Achilles tendon. Interobserver variability is not significant in the sonographic measurement of Achilles tendons. (E-mail: [email protected])

Introduction

The Achilles tendon is the largest, strongest and thickest tendon in the human body. It is one of the most common sites of overuse injuries in people participating in athletics. Hard running surfaces, training errors, poor ankle flexibility and strength are the risk factors for tendon injuries (Gibbon et al. 2000). There are many types of tendon overuse injuries, including peritendinits, tendinosis and tendon rupture (Karjalainen et al. 2000). The incidence of Achilles tendon rupture has increased over the last two decades (Maffulli et al. 1999).

High-resolution ultrasound (US) is an ideal imaging tool for initial investigation of the Achilles tendon. This is because the Achilles tendon is a superficial structure and is easily accessible by high-resolution US, which provides detailed images and has a high accuracy in the assessment of the tendon Kainberger et al 1990, Kalebo et al 1992, Gibbon et al 1999.

It has been reported that progressive thickening of the Achilles tendon was significantly correlated with Achilles tendon rupture (Nehrer et al. 1997), which is associated with sports (Jozsa et al. 1989). However, sonographic evaluation of the effect of exercise on the thickness and cross-sectional area of Achilles tendons in asymptomatic subjects has been seldom reported. Therefore, the present study was undertaken to investigate the effect of exercise on the thickness and cross-sectional area of Achilles tendons in an asymptomatic Chinese population with the use of high-resolution US.

The effect of the dominance of an ankle on Achilles tendon thickness and cross-sectional area has not been documented. Previous studies have reported on the thickness of normal Achilles tendons in an asymptomatic Caucasian population Mathieson et al 1988, Schweitzer and Karasick 2000. However, these are devoid of US reference for Achilles tendon evaluation in a Chinese population. Koivunen-Niemela and Parkkola (1995) reported that there was a difference in normal Achilles tendon thickness between Japanese subjects and Caucasian subjects. Chinese people tend to have a smaller body build than the Caucasians, and the size of Achilles tendon may also be different in Chinese and Caucasians. Therefore, this study was undertaken to evaluate the thickness and cross-sectional area of Achilles tendons in an asymptomatic Chinese population that may act as a baseline for differential diagnosis in clinical practice.

It has been reported that interobserver variation in sonographic measurement could be significant even among experienced examiners Salonen et al 1991, Zimmermann et al 2001. However, this variation may be reduced if a standardized scanning protocol is used. Therefore, this study also investigated the interobserver variability (reproducibility) in the sonographic measurement of the thickness and cross-sectional area of Achilles tendons.

This study provides baseline information on normal Achilles tendons. The information is useful to radiologists, who have an interest in musculoskeletal US in the assessment of Achilles tendons.