Movement evoked pain and mechanical hyperalgesia after intramuscular injection of nerve growth factor: a model of sustained elbow pain

Objective: Lateral epicondylalgia presents as lateral elbow pain provoked by upper limb tasks. An experimental model of elbow pain provoked by movement/muscle contraction and maintained over several days is required to better understand the mechanisms underlying sustained elbow pain. This study investigated the time course and pain location induced by nerve growth factor (NGF) injection into a wrist extensor muscle, and whether movement and muscle contraction/stretch provoked pain. Methods: On Day 0 twenty-six painfree volunteers were injected with NGF (N=13) or isotonic saline (randomized) into the extensor carpi radialis brevis (ECRB) muscle of the dominant arm. On Day 2 pain was induced in all participants by hypertonic saline injection into ECRB. A Likert scale and patient-rated tennis elbow evaluation (PRTEE) was used to assess pain and functional limitation (Days 0-10). Pain intensity during contraction/stretch of ECRB, and pressure pain thresholds (PPTs) were recorded before and after injections on Days 0 and 2, and Days 4 and 10. Results: Compared with isotonic saline, NGF evoked: i) greater Likert pain ratings from 12 hours post-injection until Day 6, ii) greater PRTEE scores on Days 2 and 4, iii) greater pain during ECRB contraction/stretch on Day 2, and iv) lower PPTs on Day 4. Conclusions: This article presents a novel experimental human pain model suitable to study the sustained effects of lateral elbow pain on sensorimotor function and to probe the mechanisms underlying persistent musculoskeletal pain.