Validation of a spring loaded probe for single and repeat pressure pain testing, including public domain specifications for design and manufacture.

Temporal summation of pressure pain is technically more challenging than simple pressure pain thresholds. The current study describes the design, manufacture and validation of a simple mechanical test apparatus to assess the temporal summation of deep pressure pain. We release design details into the public domain with the intention of providing free access for researchers especially in low income countries. Utility and validity of the probes were assessed by pressure application in three different experimental setups: A. Identifying potential issues which needed to be addressed to ensure a reliable test procedure (189 tests with 24 testers using four different probes). B. Selecting the most reliable target force curve (one tester conducted 20 tests). C. Estimating classic inter and intra-examiner reliability and comparing probe measures to other QST measures (repeated measures study with counterbalancing). We make recommendations on best use of the probes. Pressure pain thresholds assessed using probes were affected by anatomical test site and testing tool, but not by tester, day or session. Temporal summation of pressure pain was significantly greater than that of a single pressure application. We found no correlation between temporal summation using the probes on the Infra-Spinatus muscle and temporal summation using a pneumatic cuff on the lower leg. The probe was a useful tool for assessing pain intensity and temporal summation of pressure pain intensity, but not for pain thresholds. A number of caveats need to be considered when using the probe, including but not limited to audio cues and target ideal wave function.