EC Orthopaedics

Aim and Background: Strength duration curve (SDC) is a plot of the threshold (lowest) current versus pulse duration required to stimulate excitable tissue such as a nerve or muscle. It is a routinely performed procedure for clinical identification of many neuromuscular conditions. Radiculopathy is a clinical condition defined as pain and/or neurologic deficit in a specific nerve root distribution, including motor loss, sensory changes (alteration or loss), and sometimes depression of deep tendon reflexes. A common cause of radiculopathy is narrowing of the space where nerve roots exit the spine, which can be a result of stenosis, bone spurs, disc herniation or other conditions.

This review article discusses the importance of SDC in radiculopathy; its procedural approach and parameters of significance in radiculopathy; advantages and limitations; and implications for clinical practice and research.

Methods: A scoping review was conducted using electronic databases; and the keywords strength duration curve, chronaxie, rheobase, radiculopathy, disc herniation and synonymous terms.

Results: 4 studies were found involving use of chronaxie values and/or SDC in suspected cases of disc pathology. All the publications reported were primary clinical studies. Chronaxie was the most studied parameter with or without plotting of SDC.

Conclusion: Chronaxie determinants in suspected cases of lumbar disc pathology confirms diagnosis of radiculopathy; guides interspace localization of disc lesions within two disc spaces; and also can help in determining whether the disc bulge is unilateral or bilateral. SDC plotting along with chronaxiemetry improves the accuracy and reliability. This combined approach offers a reliable and reproducible method of electrodiagnosis for the detection of nerve root lesions resulting from disc pathology.

 Clinical Significance: This literature review found very few studies on clinical applications of SDC in radiculopathy. As SDC is such an easy to perform procedure in clinical practice, lack of research on the various applications of SDC undermines its utility and calls for more research to highlight its importance in diagnosing and also in determining the prognosis of radiculopathy.

 Keywords: Strength Duration Curve; Chronaxie; Rheobase; Radiculopathy; Disc Herniation; Electrodiagnosis

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