Validity of resting myotonometric assessment of lower extremity muscles in chronic stroke patients with limited hypertonia: a preliminary study.

The aim of this preliminary study was to examine the validity of a recently-introduced tool (MyotonPRO) for the assessment of mechanical parameters of the main lower extremity muscles in patients with chronic stroke. Thigh and shank muscles of 20 stroke patients with limited hypertonia (11 men and 9 women; mean age: 52±11yrs) and 20 healthy controls (11 men and 9 women; mean age: 53±10yrs) were bilaterally evaluated with (i) MyotonPRO for muscle stiffness, tone and elasticity, (ii) ultrasonography for muscle and subcutaneous thickness, and (iii) dynamometry for isometric muscle strength. MyotonPRO parameters of stroke patients were reassessed a week later (inter-day test-retest design). For all the investigated muscles, MyotonPRO variables did not differ between the more affected and the less affected side of patients (P>0.05 for main side effect), and neither differed between patients and controls (P>0.05 for main group effect), except for gastrocnemius medialis stiffness that was higher in patients (300±51N/m) than in controls (281±29N/m; P<0.05). Thigh muscle stiffness was negatively correlated to subcutaneous thickness (r=-0.84 for the vastus lateralis; P<0.001), while only tibialis anterior stiffness and tone correlated positively with muscle thickness (both r=0.46; P<0.01). Test-retest reliability of MyotonPRO parameters was adequate, except for muscle elasticity. The validity of MyotonPRO for the evaluation of thigh muscles in chronic stroke patients is partially challenged by the poor discriminant ability and by the considerable impact of subcutaneous tissue thickness (sex-dependent) on mechanical parameters. The potential validity of MyotonPRO for the assessment of shank muscles requires further investigation.