Original article
Ulnar nerve morphology on magnetic resonance imaging predicts nerve recovery after surgery for cubital tunnel syndromeLa morphologie du nerf ulnaire en imagerie par résonance magnétique prédit la récupération nerveuse après chirurgie du syndrome du tunnel cubital

https://doi.org/10.1016/j.hansur.2021.10.316Get rights and content

Abstract

Magnetic resonance imaging (MRI) can evaluate nerve morphology in cubital tunnel syndrome (CuTS), but its value in predicting surgical outcome is unclear. The purpose of this study was to determine whether ulnar nerve morphology on MRI correlated with outcome after CuTS surgery. We reviewed 40 patients who had preoperative MRI and electrodiagnostic (EDX) examinations for CuTS and outcome evaluation 6 months and 2 years postoperatively. Using MRI, ulnar nerve cross-sectional area (UNCSA), changes in signal intensity, and any space-occupying lesion were evaluated. Other factors assessed were age, symptom duration and severity, type-2 diabetes and EDX parameters. Factors associated with unfavorable surgical outcome were identified. At 6 months postoperatively, 12 patients (30%) had excellent, 19 (47.5%) good, 8 (20%) fair and 1 (2.5%) poor results on modified Wilson–Krout criteria. On univariate analysis, unfavorable outcomes were associated with increased UNCSA, space-occupying lesion, and decreased motor nerve conduction velocity (mNCV), and on multivariate analysis with increased UNCSA 1 cm distal from the epicondyle only (model 1) or increased UNCSA 1 cm proximal from the epicondyle and decreased mNCV (model 2). At 2 years, 15 patients (37.5%) had excellent, 21 (52.5%) good, 3 (7.5%) fair and 1 (2.5%) poor results, and no factors correlated with unfavorable outcome. Increased UNCSA on MRI was associated with unfavorable outcome at 6 months but not at 2 years. This study suggests that morphologic ulnar nerve changes can predict delayed nerve recovery after surgery for CuTS.

Résumé

L’imagerie par résonance magnétique (IRM) peut évaluer la morphologie nerveuse dans le syndrome du tunnel cubital (STC), mais sa valeur pour prédire les résultats chirurgicaux n’est pas claire. Le but de cette étude était de déterminer si la morphologie du nerf ulnaire en IRM était corrélée avec les résultats après chirurgie pour STC. Nous avons examiné 40 patients qui avaient subi des examens IRM et électroneuromyographiques (ENMG) pour le STC avant l’opération et ont eu des évaluations des résultats 6 mois et 2 ans après l’opération. En IRM, la section transversale du nerf ulnaire (STNU), les changements d’intensité du signal et toute lésion occupant de l’espace ont été évalués. Les autres facteurs évalués étaient l’âge, la durée et la sévérité des symptômes, le diabète sucré et les paramètres ENMG. Les facteurs associés à des résultats chirurgicaux défavorables ont été identifiés. À 6 mois postopératoires, 12 patients (30%) avaient d’excellents résultats, 19 (47,5%) bons, huit (20%) moyens et un (2,5%) mauvais selon les critères de Wilson–Krout. En analyse univariée, des résultats défavorables étaient associés à une augmentation de la STNU, à une lésion occupant l’espace et à une diminution de la vitesse de conduction nerveuse motrice (VCNm). Dans l’analyse multivariée, les résultats défavorables étaient associés à une augmentation de la STNU à 1 cm en aval de l’épicondyle uniquement (modèle 1) ou à une augmentation de la STNU à 1 cm en amont de l’épicondyle et à une diminution de la VCNm (modèle 2). À 2 ans, 15 patients (37,5%) avaient d’excellents résultats, 21 (52,5%) bons, trois (7,5%) moyens et un (2,5%) mauvais, et aucun facteur n’était corrélé avec des résultats défavorables. L’augmentation de la VCNm en IRM était associée à une issue défavorable à 6 mois, mais cette association n’était pas présente à 2 ans après la chirurgie. Cette étude suggère que les changements morphologiques du nerf ulnaire peuvent prédire la récupération nerveuse retardée après une chirurgie pour le STC.

Introduction

Cubital tunnel syndrome (CuTS) is the second most common nerve entrapment syndrome affecting the upper extremity [1], [2]. Diagnosis is based on clinical signs and symptoms, which include both motor and sensory abnormalities involving ulnar nerve distribution over the forearm and hand. Electrodiagnostic testing (EDX) and magnetic resonance imaging (MRI) aid in confirming the diagnosis, quantifying disease severity, and identifying the exact site of ulnar nerve compression [3], [4].

Several prognostic factors for poor surgical outcome have been identified: advanced age, intrinsic muscle atrophy, and prolonged symptom duration [5], [6], [7], [8]. Functional aspects of the ulnar nerve are evaluated by EDX, while MRI reveals morphological aspects such as size and signal intensity [9]. Previous studies using MRI showed its value in diagnosing CuTS [10], but its value in predicting surgical outcome is unclear [11].

The purpose of this study was to determine whether ulnar nerve morphology on MRI correlated with outcome after surgery for CuTS.

Section snippets

Patients

We obtained approval from the Institutional Review Board of our institution for this study (SNUBH IRB No: B-1905-543-109), which waived informed consent. We reviewed the medical records of patients who had surgery for CuTS at our referral teaching hospital located in an urban area, between January 2014 and June 2019. The inclusion criteria comprised surgery for CuTS and both EDX and elbow MRI examination. Diagnosis was confirmed on EDX, performed following the guidelines of the American

Baseline characteristics and MRI findings

There were 27 men and 13 women in the study, with a mean age of 48 (range, 17–75) years. Preoperatively, 15 patients (38%) were classified as McGowan grade IIA, 19 (48%) grade IIB, and six (15%) grade III (Table 1).

The ulnar nerve CSA was largest at the ME and smallest at 3 cm distal to the ME (Fig. 2). Increased ulnar nerve signal intensity changes were found in 34 subjects (85%) and increased forearm muscle signal intensity changes in 3 (8%). Ten patients (25%) had space-occupying lesions

Discussion

MRI can evaluate ulnar nerve morphology in patients with CuTS, while EDX evaluates functional aspects of the nerve. This study demonstrated that unfavorable outcomes at 6 months after surgery were associated with both large preoperative ulnar nerve CSA on MRI and low mNCV on EDX. However, these associations were not present at 2 years after surgery. Therefore, the study suggests that both morphologic changes and functional aspects of the ulnar nerve can predict delayed nerve recovery at 6

Conclusion

This study demonstrated that increased ulnar nerve cross-sectional area on MRI was associated with suboptimal improvement after surgery for CuTS at 6 months, but this relation was not present at 2 years’ follow-up. The study suggests that morphologic changes in the ulnar nerve can predict delayed nerve recovery after surgery for CuTS. Assessment of morphologic changes in the ulnar nerve can be helpful for patient consultation on the prognosis of surgery for CuTS.

Human and animal rights

The authors declare that the work described has not involved experimentation on humans or animals.

Informed consent and patient details

The authors declare that the work described does not involve patients or volunteers.

Disclosure of interest

The authors declare that they have no competing interests.

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Author contributions

All authors attest that they meet the current International Committee of Medical Journal Editors (ICMJE) criteria for authorship.

Ethics

This study obtained approval from the Institutional Review Board of our institution (No: B-1905-543-109), which waived informed consent. The authors declare that this report does not contain any personal information that could lead to the identification of patients.

Acknowledgments

The authors thank the Division of Statistics in Medical Research Collaborating Center at Seoul National University Bundang Hospital for statistical analyses.

References (28)

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1

Jong Seop Kim and Gajendra Mani Shah should be considered the co-first authors of this study.

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