Pressure Algometry and Tissue Characteristics: Improved Stimulation Efficacy by a New Probe Design

Abstract

Pressure algometry is broadly utilized to assess deep tissue sensitivity. In this study the relation between pressure-induced pain in humans and stress/strain distribution within the deep tissue was evaluated. A 3-dimensional finite-element computer model was utilized to describe stress/strain distribution in tissues of the lower leg during pressure stimulation. The computer model was validated based on data recorded by computer-controlled pressure-induced muscle pain in 6 subjects. An indentation of 7 mm was sore for all subjects and at this level data were extracted from each simulation. Simulations were performed with two probe designs (cylindrical and semispherical). The principal stress peaked in the skin and was decreased to about 10% in the underlying muscle tissue. The principal strain peaked in adipose tissue and was reduced in muscle tissue to 80%. The probe evoked a strain peak in adipose tissue at 0.12 (cylindrical) and 0.24 (semispherical); in muscle tissue 0.10 and 0.20 respectively. The shear strains were also reduced using the semispherical tip. The human pressure pain thresholds with the semispherical tip were significantly smaller compared with the flat probe (P<0.05). The results suggest that pressure-induced muscle pain is most effectively induced by semi spherical probes, while flat ones activate superficial structures. The probe design is considered an important factor during pressure pain assessments and should take into account when performing clinical studies.