The static stiffness index: a simple method to assess the elastic property of compression material in vivo

The efficacy of compression therapy depends mainly on the exerted pressure and on the stiffness of the material.

To propose a simple method by which pressure and stiffness can be assessed in the individual patient.

Using a pressure transducer (Kikuhime small probe, MediTrade, Soro, Denmark) the sub-bandage pressure is measured on the medial aspect of the lower leg at the transition of the gastrocnemius muscle into the Achilles' tendon. The pressure difference between active standing and lying is defined as the static stiffness index (SSI).

The accuracy and precision of the probe are good. Unna boot bandages (Lohmann-Rauscher, Vienna, Austria) and multilayer short-stretch bandages show a significantly higher SSI than long-stretch bandages and round-knitted class II stockings. The SSI values are lower than 10 mm Hg for elastic, long-stretch material and higher than 10 mm Hg for inelastic, short-stretch material.

In future compression trials, pressure and stiffness measured in vivo should be declared.