Shear Wave Elastography (SWE) of Asymptomatic Achilles Tendons: A Comparison Between Semiprofessional Athletes and the Nonathletic General Population

Abstract

Rationale and objectives: It has been shown that Shear Wave Elastography (SWE) is a useful tool to evaluate tendon stiffness, e.g. in diagnosing tendinopathies, as diseased or injured tendons are intra-individually softer than healthy ones. But reference values between different population groups are still missing. The purpose of this prospective clinical study was two-fold: First, to comparatively analyse Achilles tendon stiffness between asymptomatic semiprofessional athletes and an asymptomatic nonathletic control group. Second, to evaluate specificity, with which SWE is able to predict absence of clinical symptoms in asymptomatic individuals, compared to B-mode-Ultrasound (B-US) and Power Doppler-Ultrasound (PD-US).

Materials and methods: Prospective clinical study in 68 asymptomatic healthy participants, 33 (48.5%) of them semiprofessional athletes with at least five training units of running per week and 35 (51.5 %) normal nonathletic persons, asymptomatic respectively. A consecutive of 136 Achilles tendons underwent standardized multi-modal ultrasound, consisting of B-US, PD-US, and SWE (Aixplorer, Supersonic). Pathologic structural changes at B-US, increased Doppler signal PD-US and quantitative ROI-based-analysis of tendon elasticity in kilopascal (kPa) were performed in all participants. Tendon stiffness was compared intra-individually between right and left side in each participant. SWE values between athletes and nonathletes were compared by using student's t test (p < 0.05). To evaluate the ability of different sonographic modalities in predicting "absence of clinical symptoms", specificities of B-US, PD-US, and SWE were calculated and compared among each other.

Results: Mean SWE-value for Achilles tendon was 183.8 kPa (± 98 kPa) in athletes and 103.6 kPa (± 30.5 kPa) in the nonathletic control group. The difference between athletes and non-athletes was statistically significant (p < 0.001). No significant differences were found intra-individually between right and left side: athlete mean: right: 187.2 kPa (SD ± 45.2 kPa)/left: 180.4 kPa (SD 39.7 kPa); nonathlete mean: right: 105.4 kPa (SD 34.9 kPa)/left: 101.8 kPa (SD 28.9 kPa). Specificity with which asymptomatic tendons were rated as "inconspicuous" was 60.6% for B-US, 93.9% for PD-US and 96.3% for SWE.

Conclusion: Healthy athletes exhibit significantly higher SWE-values in Achilles tendons than healthy nonathletic participants, which means that they have significantly stiffer tendons, possibly caused by repeated training. SWE is able to measure and display these effects. These interindividual differences should be taken into consideration, especially when rating a tendon as "healthy" or "diseased", because a "softer" tendon does not necessarily mean to be affected.

Keywords: Achilles; Healthy athletes; Healthy nonathletes; Reference values; SWE.