Our ability to sense the position of our body, known as proprioception, is fundamental for controlling how we move and interact during daily activities (Proske and Gandevia, 2012). People who have persistent pain (i.e., pain that lasts for more than three months) find it difficult to sense the position of their painful limb or body part in space (Stanton et al., 2016). This is particularly important as poor body position sense is thought to reflect impairments in proprioceptive function that may lead to an increased risk of injury/reoccurrence of symptoms (Roijezon, Clark, and Treleaven, 2015).
However, exactly when these impairments occur in the transition to persistent pain is unknown. Understanding the time-point at which these impairments occur is essential to help identify why some people develop persistent pain while others do not, and to facilitate the delivery of treatment at meaningful time-points.
When researchers test body position sense, they often use a joint reposition task (Proske and Gandevia, 2012). This task involves a person moving their limb (or somebody moving their limb) to a set position, typically with their eyes closed. That person is then assessed on how well they can re-position their limb back to the same start position, providing an indication of joint position sense.
In our study, we used a joint reposition task and an experimental pain model thought to mimic the symptoms (pain and muscle soreness) and mechanisms involved in the transition to persistent musculoskeletal pain (Bergin et al., 2015). The experimental pain model involved two injections of nerve growth factor into a forearm extensor muscle, which has been shown to induce persistent forearm muscle pain for up to 14 days (Schabrun et al., 2016).
We examined the effect of this experimental pain on joint position sense in 28 healthy individuals. Measurements of joint position sense where taken at baseline (when participants were pain-free), during the first four days following the injections (when pain was present), and then again 10 days later (when pain had resolved).
WHAT DID WE FIND?
The injection of nerve growth factor into the forearm elicited mild pain (3-3.5/10) within the first four days, with pain mostly gone by Day 14 (0.3/10). To assess whether persistent experiment pain influenced joint position sense, we compared position sense measurements during the four days of pain to baseline measurements.
Our results showed that joint position sense was no different when assessed over four-days of pain than when assessed in a pain-free state at baseline or following the resolution of pain. For example, the absolute reposition error at baseline for radial deviation was 1.7 degrees. During mild pain, the absolute reposition error was 1.8 degrees on Day 2 and 1.9 degrees on Day 4. Similarly small differences were seen ulnar deviation for reposition error (1.5, 1.7 and 1.8 degrees for baseline, Day 2 and Day 4, respectively).
SIGNIFICANCE AND IMPLICATIONS
This is the first study to show that joint position sense is unaffected during the progressive development and persistence of experimentally-induced musculoskeletal pain over a four-day period. However, our methods did not assess joint position sense beyond four days of persistent pain. One possibility is that a longer duration of pain may be required to interfere with position sense and replicate the deficits observed in a persistent pain population. The findings from our study suggest that proprioceptive function is intact in the early stages of a pain episode (up to four days), and that treatments which aim to restore proprioception may not be required within this early stage of a pain experience.
Summers SJ, Schabrun SM, Hirata RP, Graven-Nielsen T, Cavaleri R, Chipchase LS. Effect of sustained experimental muscle pain on joint position sense. Pain Rep 4(3):e737, 2019.
Bergin MJG, Hirata R, Mista C, Christensen SW, Tucker K, Vicenzino B, Hodges P, Graven‐Nielsen T. Movement evoked pain and mechanical hyperalgesia after intramuscular injection of nerve growth factor: a model of sustained elbow pain. Pain Med 16:2180-91, 2015.
Proske U, Gandevia SC. The Proprioceptive Senses: Their Roles in Signaling Body Shape, Body Position and Movement, and Muscle Force. Physiol Rev 92: 1651-1697, 2012.
Roijezon U, Clark NC, Treleaven J. Proprioception in musculoskeletal rehabilitation. Part 1: Basic science and principles of assessment and clinical interventions. Man Ther 20:368-77, 2015.
Schabrun SM, Christensen SW, Mrachacz-Kersting N, Graven-Nielsen T. Motor cortex reorganization and impaired function in the transition to sustained muscle pain. Cereb Cortex. 26:1878-90, 2016.
Stanton TR, Leake HB, Chalmers KJ, Moseley GL. Evidence of Impaired Proprioception in Chronic, Idiopathic Neck Pain: Systematic Review and Meta-Analysis. Phys Ther 96:876-87, 2016.
Simon Summers is a PhD candidate at Western Sydney University and Research Associate at the University of Canberra Research Institute for Sport and Exercise (UCRISE). His area of research focuses on understanding the neurobiological mechanisms that underpin the transition from acute to persistent pain.