Disclosures: Anita M. Lowe Taylor, MD: No financial relationships or conflicts of interest
Objective: Falls are the leading cause of injuries among older patients in the United States. Easy detection of those at risk may lead to prevention opportunities. Given prior work suggesting that a fibular compound muscle action potential (CMAP) < 4.0 mV when recording at the extensor digitorum brevis (EDB) muscle predicts impairment of ankle proprioceptive precision and increased fall risk, we assessed whether simple clinical inspection of EDB muscle bulk can predict fibular nerve CMAP above or below this functionally relevant 4.0 mV threshold.
Design: Two investigators independently graded EDB muscle bulk as 1) normal bulk, 2) diminished bulk, or 3) severe atrophy. Following this, fibular motor nerve conduction studies at the ankle were completed as per AANEM guidelines. Setting : Outpatient PM&R EMG clinics.
Participants : 52 adult participants representing 102 feet.
Interventions: None
Main Outcome Measures: 1) Interrater reliability of clinical evaluation of EDB muscle bulk, and 2) Determine whether EDB muscle bulk is predictive of fibular nerve CMAP amplitude.
Results: Cohen’s Kappa value was 0.64 indicating good inter-rater reliability when using binary ratings (1= normal bulk, 2 or 3= abnormal bulk). The primary investigator was correct in predicting CMAP values above or below 4.0 mV 82% of the time (89% when muscle bulk was normal, 67% when muscle bulk was abnormal). When there was severe muscle atrophy, the prediction was correct 100% of the time (8/8). The mean CMAP value was 5.9mV when muscle bulk was graded as normal, 3.4mV when graded as diminished, and 0.6mV when graded as severe atrophy. Conclusions: There was good inter-rater reliability when grading EDB bulk as normal or abnormal. EDB muscle bulk was predictive of fibular CMAP above or below 4.0mV and may represent a quick and easy clinical surrogate marker for fall risk.
Level of Evidence: Level I
To cite this abstract in AMA style:
Taylor AML, Levin JR. Extensor Digitorum Brevis Bulk as an Indicator of Fibular Motor Nerve Conduction Amplitude and Marker of Fall Risk [abstract]. PM R. 2020; 12(S1)(suppl 1). https://pmrjabstracts.org/abstract/extensor-digitorum-brevis-bulk-as-an-indicator-of-fibular-motor-nerve-conduction-amplitude-and-marker-of-fall-risk/. Accessed May 31, 2025.« Back to AAPM&R Annual Assembly 2020
PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/extensor-digitorum-brevis-bulk-as-an-indicator-of-fibular-motor-nerve-conduction-amplitude-and-marker-of-fall-risk/