Pain Tolerance Self-Assessment vs Objective Pressure Sensitivity: Do Patients Accurately Estimate Their Own Pain Tolerance?

CATEGORY: Basic Sciences/Biologics; Other INTRODUCTION/PURPOSE: Effective pain treatment remains elusive in the orthopedic foot and ankle practice as evidenced by the variable experience of pain, post-operative or otherwise. Intrinsic pain tolerance is likely contributing to this variability in the patient's experience of pain. Pressure dolorimetry is a validated, objective measure to assess pressure sensitivity and is correlated with pain tolerance. No previous study in the orthopedic foot and ankle literature has attempted to correlate objective versus subjective pain tolerance. General mental health is associated with central pain sensitization and may also affect pain tolerance. Our hypothesis was that subjective self-assessment of pain tolerance would be correlated with objective dolorimetry. We hypothesized that mental patient-reported outcome scores would also be correlated to objective pain tolerance. METHODS: Prospectively-collected patient-reported outcome scores (PROMIS), dolorimetry measurements, and survey data of subjective reported pain tolerance were collected pre-operatively on 50 consecutive patients by two surgeons in an urban orthopedic foot and ankle practice. Patients were included if they had normal sensation on the plantar foot and no prior surgery or plantar heel source of pain. Each patient underwent objective measurement of their ability to withstand pressure applied to the plantar heel causing 5/10 pain using a hand-held dolorimeter with digital pressure measurement display. Each patient was administered a preoperative battery of PROMIS physical function (PF), pain interference (PI), and mood/depression (M) instruments, and a separate survey where they scaled their subjective tolerance to pain and discomfort. Statistical analysis was performed utilizing students t-test for continuous variables. Correlations were evaluated with Pearson's R coefficient. Data are reported as means (+/- standard deviation) unless otherwise noted. RESULTS: 50 patients received hand-held dolorimetry measurements, completed the pain tolerance survey, and completed PROMIS measures. Dolorimetry data from the plantar heel was normally distributed with mean force 24 N/cm(2) (+/-10) to reflect a 5/10 pain experienced by the patient. Patients were shown to estimate their pain threshold with mean subjective pain threshold 6.8/10 (+/-2) regardless of objective pain data or PROMIS scores. The mean PROMIS scores of the sample were PF (41+/-8), PI (60+/-7), and M (49+/-9) reflecting a sample with decreased physical function and increased pain which could be expected in an outpatient foot and ankle clinic. There was a negative correlation of R=(-0.432) regarding PROMIS-M with dolorimetry objective pain tolerance which was statistically significant (p<-0.05). Patients had more features of depression/anxiety (PROMIS-M score >60) had a statistically significant decrease in pain threshold to 18+/-8 N/cm(2) compared to 30 +/- 9 N/cm(2) for those who were less depressed (p<0.01)). CONCLUSION: Subjective self assessment of pain tolerance is not well correlated to objective pain threshold data or other markers of mental health, and should not influence medical decision-making. Features of depression on PROMIS-M are associated with an objectively lower pain threshold which is in agreement with prior findings of central pain sensitization in patients with depression and anxiety in other studies. Future work is required to correlate dolorimetry data with post-operative medication utilization, and patient-reported outcome measures after surgery.