Quantitative ultrasound imaging of intrinsic hand muscles after traumatic cervical spinal cord injury

Ulnar compound muscle action potentials predict hand muscle strength 1 year after cervical spinal cord injury: A retrospective analysis

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.

The strength of associations between ultrasound measures of upper limb muscle morphology and isometric muscle strength: An exploratory study

INTRODUCTION/AIMS

Assessing upper limb muscle strength is important for understanding health outcomes, such as daily function and mortality. Ultrasound (US) is increasingly used to evaluate muscle health, but the relationship between its measures of morphology and isometric strength has not been thoroughly explored in upper limb muscles. The aim of this study was to evaluate the associations between US morphological measures and isometric strength in functionally relevant upper limb muscles in healthy adults.

METHODS

Twenty-four healthy volunteers (30.0 ± 10.8 years) underwent B-mode, axial US scans of the first dorsal interosseus (FDI), flexor pollicis longus (FPL), biceps brachii (BB), brachialis (BR), and triceps brachii lateral head (TB). Participants performed corresponding maximal voluntary contractions (MVC), including first digit distal phalanx flexion, second digit abduction, and elbow flexion and extension. US images were segmented to obtain maximal muscle thickness (MT) and cross-sectional area (CSA).

RESULTS

Strong positive correlations were found between muscle strength and BB MT (r = .83; p < .001), BR CSA (r = .84; p < .001), and TB MT (r = .70; p < .001). Moderate positive correlations were found for strength and FDI CSA (r = .67; p < .001), FDI MT (r = .47; p < .05), FPL CSA (r = .54; p < .01), and FPL MT (r = .42; p < .05). No significant correlation was found between strength and BR MT (r = .16; p > .05).

DISCUSSION

Our data showed moderate-to-strong associations between US muscle morphology and strength, suggesting that US is likely a good biomarker for strength. However, its use is not "one size fits all." Future investigations should continue to assess this relationship in different muscles and expand the generalizability to clinical populations.

Nerve Transfer After Cervical Spinal Cord Injury: Who Has a "Time Sensitive" Injury Based on Electrodiagnostic Findings?

OBJECTIVE

To use the ulnar compound muscle action potential (CMAP) to abductor digiti minimi (ADM) to identify the proportion of individuals with cervical spinal cord injury (SCI) who have lower motor neuron (LMN) abnormalities involving the C8-T1 spinal nerve roots, within 3-6 months, and thus may influence the response to nerve transfer surgery.

DESIGN

Retrospective analysis of prospectively collected data. Data were analyzed from European Multicenter Study About SCI database.

SETTING

Multi-center, academic hospitals.

PARTICIPANTS

We included 79 subjects (age=41.4±17.7, range:16-75; 59 men; N=79), who were classified as cervical level injuries 2 weeks after injury and who had manual muscle strength examinations that would warrant consideration for nerve transfer (C5≥4, C8<3).

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

The ulnar nerve CMAP amplitude to ADM was used as a proxy measure for C8-T1 spinal segment health. CMAP amplitude was stratified into very abnormal (<1.0 mV), sub-normal (1.0-5.9 mV), and normal (>6.0 mV). Analysis took place at 3 (n=148 limbs) and 6 months (n=145 limbs).

RESULTS

At 3- and 6-month post-injury, 33.1% and 28.3% of limbs had very abnormal CMAP amplitudes, respectively, while in 54.1% and 51.7%, CMAPs were sub-normal. Median change in amplitude from 3 to 6 months was 0.0 mV for very abnormal and 1.0 mV for subnormal groups. A 3-month ulnar CMAP <1 mV had a positive predictive value of 0.73 (95% CI 0.69-0.76) and 0.78 (95% CI 0.75-0.80) for C8 and T1 muscle strength of 0 vs 1 or 2.

CONCLUSION

A high proportion of individuals have ulnar CMAPs below the lower limit of normal 3- and 6-month post cervical SCI and may also have intercurrent LMN injury. Failure to identify individuals with LMN denervation could result in a lost opportunity to improve hand function through timely nerve transfer surgeries.

Ultrasound of the palmar aspect of the hand: normal anatomy and clinical applications of intrinsic muscles imaging

Intrinsic hand muscles play a fundamental role in tuning the fine motricity of the hand and may be affected by several pathologic conditions, including traumatic injuries, atrophic changes induced by denervation, and space-occupying masses. Modern hand surgery techniques allow to target several hand muscle pathologies and, as a direct consequence, requests for hand imaging now carry increasingly complex diagnostic questions. The progressive refinement of ultrasound technology and the current availability of high and ultra-high frequency linear transducers that allow the investigation of intrinsic hand muscles and tendons with incomparable resolution have made this modality an essential tool for the evaluation of pathological processes involving these tiny structures. Indeed, intrinsic hand muscles lie in a superficial position and are amenable to investigation by means of transducers with frequency bands superior to 20 MHz, offering clear advantages in terms of resolution and costs compared to magnetic resonance imaging. In addition, ultrasound allows to perform dynamic maneuvers that can critically enhance its diagnostic power, by examining the questioned structure during stress tests that simulate the conditions eliciting clinical symptoms. The present article aims to review the anatomy, the ultrasound scanning technique, and the clinical application of thenar, hypothenar, lumbricals and interossei muscles imaging, also showing some examples of pathology involving these structures.