Introduction: Assessment of nerve root decompression in spinal surgery is largely based on visualization and tactile feedback, particularly in minimally invasive surgery. Electromyography (EMG) has been proposed as a tool to assess decompression, but EMG responses are often difficult to quantify. Alternatively, mechanomyography (MMG) provides a quantifiable response with minimal signal to noise ratio compared to EMG. MMG is a sensitive tool to accurately quantify mechanical responses to motor action potentials generated by electrical stimulus, allowing more reliable assessment of nerve decompression.
Methods: Seventy-two (72) nerves roots in 46 patients undergoing lumbar decompression procedures were examined using MMG. Nerves were stimulated upstream from the compression site and the lowest threshold current needed to generate a muscle response was determined. Signal response sizes were recorded before and after decompression. Visual-analog scale (VAS) scores were collected pre and post-operatively.
Results: Ninety percent (90%) of patients (65/72) had elevated stimulation thresholds (>1mA) prior to decompression. After decompression, 98% of patients (64/65) with elevated current thresholds exhibited a drop in threshold of = 1mA (p<0.001). A post-decompression increase in response amplitude was recorded in all patients. VAS scores improved post-decompression (6.8 vs. 1.1, p<0.001) with a positive correlation between decreased stimulation thresholds and improved VAS scores (p<0.001).
Conclusions: MMG is an effective tool that can be used to differentiate normal and compressed nerves by quantifying the mechanomyographic response to a stimulating current. MMG allows one to quantify the effect of decompression, in real time, eliminating the subjectivity seen in tactile feedback methods. Intra-operative MMG can provide the surgeon with immediate feedback allowing for additional or alternative procedures to ensure complete nerve root decompression.
Patient Care: Improve decompression outcomes
Learning Objectives: Use of MMG in nerve root decompression