Reliability and discriminative validity of real-time ultrasound elastography in the assessment of tissue stiffness after calf muscle injury

Abstract

ObjectiveTo investigate the reliability and discriminative validity of real-time ultrasound elastography (RTE) measures of soft-tissue elasticity after calf muscle tear. DesignCross-sectional, intra/inter-examiner reliability and comparative validity study. SettingDepartment of Physical Therapy. ParticipantsTwenty-one recreational athletes were included and examined 6 weeks after sustaining a grade I-II calf musculature tear. Main outcome measuresSoft-tissue elasticity was measured by two experienced assessors using RTE assessments in both the longitudinal and transverse planes of the athletes’ injured and uninjured calf muscles. Elasticity was estimated by using the strain ratio (SR), which was calculated by dividing the strain (displacement) value taken at the medial gastrocnemius-soleus myotendinous junction (reference) by the strain value taken at the centre of the injury (index) as visualized on B-mode sonogram. Intra- and inter-observer reliability was estimated calculating intra-class correlation coefficients (ICCs) and standard error of measurement (SEM). Differences in elasticity between injured and healthy legs were assessed using t-tests or Wilcoxon tests for repeated measures. ResultsAll RTE assessments in both planes showed ICC values ranging from 0.77 to 0.95 and SEM values ranging from 0.72 to 0.99. Additionally, RTE enabled both assessors to determine differences in elastic properties between injured and control legs (p < 0.001). ConclusionRTE measures of calf muscles demonstrated good reliability and were able to differentiate injured from non-injured muscle tissue. RTE may provide a fast and objective measure in sports medicine to improve the detection of risk factors for muscle injury related to alterations of the mechanical behaviour of soft tissues during healing process.