Healthy Pain-Free Individuals with a History of Distal Radius Fracture Demonstrate an Expanded Distribution of Experimental Referred Pain Toward the Wrist.

Abstract

Nociception caused by injuries may sensitize central mechanisms causing expanded pain areas. After recovery, the status of such pain distribution and sensitivity mechanisms is unknown. The present study investigated whether individuals who have fully recovered from a distal radius fracture demonstrate increased pain sensitivity and expanded distribution of pressure-induced pain. Cross-sectional single-blinded study. Clinical setting. Twenty-three pain-free individuals with a history of painful distal radius fracture and 22 nonfractured, age/gender-matched controls participated in two experimental sessions (day 0, day 1) 24 hours apart. Pressure pain thresholds (PPTs) were recorded bilaterally at the extensor carpi radialis longus (ECRL), infraspinatus, and gastrocnemius muscles. Spatial distribution of pain was assessed following 60-second painful pressure stimulation at the ECRL (bilateral) and the infraspinatus muscles on the fractured or dominant side. Participants drew pain areas on a body map. After day 0 assessments, prolonged pain was induced by eccentric exercise of wrist extensors on the fractured/dominant side. Compared with controls, pressure-induced ECRL pain in the fracture group referred more frequently toward the distal forearm (P < 0.005) on day 0. Both groups showed larger pain areas on day 1 compared with day 0 (P < 0.005), although the fracture group showed a larger relative change between days (P < 0.005). The fracture group showed larger pain areas on the fracture side compared with the contralateral side on both days (P < 0.005). Prolonged pain and recovered prior painful injuries like fractures may sensitize pain mechanisms manifested as expanded pain distribution. Pressure-induced referred pain can be a simple pain biomarker for clinical use.