Ulnar compound muscle action potentials predict hand muscle strength one year after cervical spinal cord injury: a retrospective analysis - 13/03/25

Doi : 10.1016/j.rehab.2025.101959

Lukas D Linde ^1,², Jana Dengler ^3,⁴, Armin Curt ⁵, Martin Schubert ⁵, Rainer Abel ⁶, Norbert Weidner ⁷, Frank Röhrich ⁸, Michael J Berger ^1,^9,^{⁎
Denotes co-senior author.}, ^⁎ , Ida K Fox ^10,^{⁎
Denotes co-senior author.}
¹ International Collaboration on Repair Discoveries (ICORD), University of British Columbia, 818 West 10th Avenue, Vancouver, British Columbia, V5Z 1M9, Canada
² Department of Anesthesiology, Pharmacology and Therapeutics, Faculty of Medicine, University of British Columbia, 2775 Laurel Street, Vancouver, British Columbia, V5Z 1M9, Canada
³ Division of Plastic Surgery, Tory Trauma Program, Sunnybrook Health Sciences Centre, 2075 Bayview Avenue, Toronto, Ontario, M4N 3M5, Canada
⁴ Division of Plastic, Reconstructive and Aesthetic Surgery, Department of Surgery, University of Toronto, 555 University Avenue, Room 5426, Toronto, Ontario, M5G 1×8, Canada
⁵ Spinal Cord Injury Center, Balgrist University Hospital, Forchstrasse 340, 8008 Zurich, Switzerland
⁶ Hohe Warte Bayreuth, Hohe Warte 5, 95445 Bayreuth, Germany
⁷ Spinal Cord Injury Center, Heidelberg University Hospital, Im Neuenheimer Feld 400, 69120 Heidelberg, Germany
⁸ BG Klinikum Bergmannstrost, Zentrum für Rückenmarkverletzte und Klinik für Orthopädie, Merseburger Str 165, 06112 Halle, Germany
⁹ Division of Physical Medicine & Rehabilitation, Department of Medicine, University of British Columbia, 2775 Laurel Street, Vancouver, BC V5Z 1M9, Canada
¹⁰ Division of Plastic and Reconstructive Surgery, Department of Surgery, Washington University School of Medicine, 660 S. Euclid Avenue, St. Louis, Missouri, 63110, USA

^#Corresponding Author: Michael J. Berger, ICORD-BSCC, 818 W 10th Ave, Vancouver, BC, V5Z 1M9, (604) 675-8800ICORD-BSCC818 W 10th AveVancouverBCV5Z 1M9

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Highlights

•	The ulnar compound muscle action potential (CMAP) indicates hand muscle strength
•	Spinal cord injury (SCI) affects the CMAP and hand muscle strength
•	The 3-month ulnar CMAP predicts hand muscle strength 12 months after SCI
•	The 3-month ulnar CMAP is related to functional outcomes 12 months after SCI

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Abstract

Background

Lower motor neuron (LMN) dysfunction caused by anterior horn cell damage in the ventral gray matter during spinal cord injury (SCI) may impact long-term prognosis.

Objectives

To determine the influence of the 3-month ulnar compound muscle action potentials (CMAP; representative of C8-T1 spinal segmental LMN integrity) on hand muscle strength and function, 12 months following SCI.

Methods

We completed retrospective analyses of the European Multicenter Study about SCI (EMSCI) database. Included participants had traumatic SCI (motor complete or incomplete), initial neurological level of injury C1-C8, and ulnar CMAP from the abductor digiti minimi in at least one limb, 3 months after injury. We trichotomized 3-month ulnar CMAP into absent (CMAP = 0.0 mV), reduced (CMAP <6.0 mV), and normal (CMAP ≥6.0 mV), and constructed logistical regression models to predict 12-month C8 and T1 motor scores, dichotomized into poor (≤3) and functional (>3). We explored relationships between trichotomized 3-month ulnar CMAP and 12-month functional Graded Redefined Assessment of Strength, Sensation and Prehension (GRASSP) and Spinal Cord Independence Measure (SCIM) upper limb sub-scales, using non-parametric statistics.

Results

Data from 318 participants (253 males), 46.8 years old (SD 18.4), resulted in CMAP and corresponding motor scores in 629 limbs. Adjusted logistical regression models were significant for C8 and T1 motor scores, with absent (C8 36.6, 95% CI 12.9-133; T1 38.7, 95% CI 11.2-24) and reduced (C8 11.0, 95% CI 6.7-18.4; T1 7.93, 95% CI 5.2-12.3) CMAP, predictive of poor 12-month motor scores. 12-month GRASSP (n = 30) and SCIM scores were significantly higher in those with normal 3-month ulnar CMAPs than absent and reduced.

Conclusion

There is a 7 to 38-fold higher likelihood that SCI individuals with reduced or absent 3-month ulnar CMAP will demonstrate poor hand motor scores at 12 months. This aligns with significantly worse GRASSP and SCIM functional scores. Our findings justify adding LMN health measures in prognostic modeling after SCI.

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Keywords : Spinal cord injury, Upper limb, Motor recovery, Compound muscle action potential

Abbreviations : ADM, AIS, CI, CMAP, EMG, EMSCI, GRASSP, ISNCSCI, LMN, MEP, NCS, ROC, SCI, SCIM, SD, UMN