Reliability of the use of foot pressure pain threshold in adults: a test-retest analysis.

Background: Foot pain is very common, affecting 24% of the adult population over 45 years old. Mechanical stimulation devices, such as pressure algometers, are used for the precise and objective quantification of the pain threshold (minimum tolerable pain). The digital pressure algometer is a diagnostic tool for evaluating pain thresholds and pain tolerance related to musculoskeletal conditions in patients. Pressure pain thresholds (PPT) measured with a digital algometer have shown good to excellent intra-rater agreement and reliability for most body locations. However, no study has focused on evaluating specific locations on the foot. This study aimed to determine the intra- and inter-session agreement and reliability of pressure pain threshold measurements on the foot in a population of adults aged 55 to 75 years. Method: Using a JTECH Commander digital algometer, an experienced podiatrist measured the pressure pain thresholds at four locations on the sole of the dominant and non-dominant foot (head of the first metatarsal, head of the fifth metatarsal, pulp of the first toe, and center of the heel) in 15 male and 16 female volunteers aged 55 to 75. In each session, three pressure pain thresholds measurements were taken at each location. Measurements were repeated over three different sessions; the first and second sessions were 30 min apart, and the third session was 1 week later. The standard error of measurement (SEM) and coefficient of variation (CV) were calculated to reflect within- and between-session agreement. Reliability was assessed using intraclass correlation coefficients (ICC). Results: Within-session agreement, expressed as SEM, ranged from 3Newtons (N) to 8N depending on the test location. Between session agreement, expressed as SEM, ranged from 5N to 10N, and the CV ranged from 7.9% to 13.7% per location. The ICC values ranged from 0.76 to 0.91. Conclusions: A digital algometer can be used to measure pressure pain thresholds on the foot. Specifically, this study used this technique to evaluate PPT at four points on the plantar surface (head of the first and fifth metatarsals, pulp of the first toe, and center of the heel), and the results showed good to excellent reliability for within- and between-session measurements.