Individuals with Recurrent Low Back Pain Exhibit Significant Changes of Paraspinal Muscle Performance after Lumbar Multifidus Intramuscular Fine Wire Electrode Insertion

Abstract

STUDY DESIGN: Case control study. BACKGROUND: Recurrent low back pain (RLBP) is associated with paraspinal muscle dysfunction. Intramuscular electromyography (EMG) is a common tool for studying activation of the deep lumbar paraspinal muscles such as multifidi muscles, but it is currently currently unclear how muscle performance and activation are affected by the pain and micro-injury associated with intramuscular fine-wire electrode (IFWE) insertion and how it interacts with the presence of RLBP. OBJECTIVES: The purpose of this study was to examine how IFWE insertion into the lumbar multifidus affects paraspinal muscle strength and endurance in subjects with and without RLBP. METHODS: Forty subjects aged 18 - 40 were recruited; 20 subjects with a history of RLBP were compared with a group of 20 age-matched controls with no RLBP. Paraspinal extensor strength and endurance were measured under three conditions over three testing days. On Day 1, the baseline condition (BL), we obtained preliminary measures of discomfort, force production, endurance, and muscle activation. On Days 2 and 3, the participants randomly alternated between the two experimental conditions: (i) a wire-in condition (WI) in which the IFWE was inserted and remained within the muscle and (ii) a wire-out condition (WO) in which the IFWE was inserted and immediately removed. Participants were blinded to the order of the fine-wire conditions. Subjective pain levels were recorded via the Visual Analog Scale at specific time points throughout the testing protocol. RESULTS: Individuals with RLBP showed a significant decrease in strength in both conditions that involved IFWE insertion. Controls showed no significant difference in strength across conditions. Both groups exhibited similar performance in the endurance test. CONCLUSION: Our findings indicate IFWE insertion into lumbar multifidus may lead to reduced peak spinal extensor muscle force production in individuals with a history of RLBP compared to healthy controls.