Abstract
Background: Musculoskeletal pain disorders are among the leading causes of years lived with disability worldwide representing a significant burden to society. Studies investigating a “nociceptive-fusimotor” relationship using experimentally-induced pain/noxious stimuli and muscle spindle afferent (MSA) response have been published over several decades. The purpose of this scoping review was to systematically identify and summarize research findings related to the impact of experimentally-induced pain or noxious stimulation on direct MSA discharge/response.Methods: PubMed, Cumulative Index to Nursing and Allied Health Literature (CINAHL), Cochrane and Embase were searched from database inception to August 2020. Eligible studies were: (a) published in English; (b) clinical or pre-clinical studies; (c) original data studies; (d) included the investigation of MSA response to experimentally-induced pain or noxious stimulation; (e) included quantification of at least one direct physiological measure associated with MSA activity/response. Two-phase screening procedures were conducted by a pair of independent reviewers and data extracted from eligible studies.Results: The literature search resulted in 195 articles of which 23 met inclusion criteria. Six studies (26%) were classified as clinical and 17 (74%) as pre-clinical. Two clinical studies investigated the effects of sacral dermatome pin-pricking on MSA response, while the remaining 4 studies investigated the effects of tonic muscle and/or skin pain induced by injection/infusion of hypertonic saline into the tibialis anterior muscle or subdermal tissues. In pre-clinical studies, muscle pain was induced by injection of noxious substances or the surgical removal of the meniscus at the knee joint.Conclusion: Clinical studies in awake humans reported that experimentally-induced pain did not affect, or else slightly decreased MSA spontaneous discharge and/or response during weak dorsiflexor muscle contraction, thus failing to support an excitatory nociceptive-fusimotor relationship. However, a majority of pre-clinical studies indicated that ipsilateral and contralateral muscle injection of noxious substances altered MSA resting discharge and/or response to stretch predominately through static fusimotor reflex mechanisms. Methodological differences (use of anesthesia, stretch methodology, etc.) may ultimately be responsible for the discrepancies between clinical and pre-clinical findings. Additional investigative efforts are needed to reconcile these discrepancies and to clearly establish or refute the existence of nociceptive-fusimotor relationship in muscular pain.
Highlights
Musculoskeletal pain disorders are among the leading causes of years lived with disability worldwide with low back and neck pain being listed as the most disabling musculoskeletal conditions (Brooks, 2006; Vos et al, 2017)
Clinical studies have long reported proprioception and motor control deficits associated with musculoskeletal pain (Revel et al, 1991; Brumagne et al, 1999; Taimela et al, 1999; Koumantakis et al, 2002) suggesting that chemosensitive group III and IV muscle afferents may directly contribute to a “nociceptivefusimotor” relationship via their supraspinal projections and/or effects on the fusimotor-muscle spindle afferent (MSA) system
Significant experimental limitations are associated with both clinical and preclinical studies. These limitations include: (1) the physical invasiveness required to directly record MSA response often limited the number of afferents recorded in a majority of clinical studies, (2) the inability to determine the specific role anesthesia plays on descending and/or segmental excitatory and/or inhibitory circuitry related to fusimotor drive, (3) the inability to detach ligaments from their insertion to allow near maximal stretch of the muscle in human studies, and (4) differences in delivery methodology (i.m., i.a., i.v; injection, infusion) and the inherent chemical properties, physiological interactions, and/or concentrations of noxious substances used (HS, KCl, NaCl, bradykinin, etc.) used to experimentally induce pain or provide noxious stimulation. Limitations associated with this scoping review include: (1) limiting publications in English only potentially reducing the number of studies being retrieved from the literature search; (2) excluding articles looking at indirect measures of muscle spindle responsiveness which narrowed the focus and reduced the total number of studies retrieved from the literature search; and (3) this review primarily focused on the investigation of physiological outcomes, the analysis of pain severity and/or behavioral outcomes could potentially expand on the appraisal of different experimental preparations
Summary
Musculoskeletal pain disorders are among the leading causes of years lived with disability worldwide with low back and neck pain being listed as the most disabling musculoskeletal conditions (Brooks, 2006; Vos et al, 2017). Studies investigating a “nociceptive-fusimotor” relationship using experimentally-induced pain/noxious stimuli and muscle spindle afferent (MSA) response have been published over several decades. The purpose of this scoping review was to systematically identify and summarize research findings related to the impact of experimentally-induced pain or noxious stimulation on direct MSA discharge/response
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
