Pain evoked by pressure stimulation on the tibia bone - influence of probe diameter on tissue stress and strain

The fundamental aspects of bone associated pain in humans are not fully understood. In this study pressure pain applied to the tibia bone was investigated experimentally in humans and by means of computer simulations. In humans, the pressure pain sensitivity and the relation between tissue indentation and pressure intensity were recorded by a computer-controlled pressure algometer with two different probe sizes (0.03 cm(2) and 1.0 cm(2)). The simulation-model was validated by the experimental pressure-indentation data and described tissue stress and strain distribution during pressure stimulation. Tissue stress and strain were extracted from the simulation models at the indentation equal to the pressure pain threshold. The pressure pain threshold was higher for the large compared with the small probe size (P < 0.05). This is in accordance with the simulation model where the strain in the interface between subcutaneous adipose tissue and bone was lowest with the large probe compared with the small probe when applying indentations similar to the pressure pain thresholds. For both probes the strain peaked in adipose tissue at 0.29, and in the bone interface it was reduced by 3% (0.03 cm(2)) and 15% (1.0 cm(2)), respectively. For both probes the stress peaked at 235 kPa in skin layer, and in the deeper layers it was reduced to 50 kPa. Mechanosensitive nociceptors innervating the periosteum are ideally placed to mediate pain evoked by pressure stimulation on the tibia bone and small diameter probes may be optimal for assessing bone associated pain sensitivity.