Evaluation of sonographic ulnar nerve cross-sectional area cutoff values at and around the medial epicondyle for diagnosing ulnar neuropathy at the elbow in wheelchair users.

BACKGROUND

Cubital tunnel syndrome (CuTS) is a frequent complication in wheelchair users, but optimal sonographic cross-sectional area (CSA) cutoff values and their diagnostic performances remain unclear. Electrodiagnosis studies for confirmation can be uncomfortable and may require another visit.

AIM: To evaluate the diagnostic performance of the sonographic ulnar nerve CSA (CSA-U) cutoff value of 10 mm2, and to identify alternative CSA-U cutoffs and assess their diagnostic accuracy at and around the medial epicondyle.

DESIGN

Single-centre, prospective, observational, cross-sectional study.

SETTING

Outpatient rehabilitation clinic.

POPULATION: Wheelchair users aged ≥20 years with spinal cord injury or lesion.

METHODS

Participants completed a CuTS symptom questionnaire, underwent ultrasonographic CSA measurements at the medial epicondyle (ME) and 2 cm proximal (P2) and distal (D2) to it, and electrodiagnostic studies. CuTS was confirmed by clinical symptoms and positive electrodiagnostic findings. Diagnostic performance was evaluated using the area under the receiver operating characteristic curve (AuROC), sensitivity, and specificity across CSA cutoffs.

RESULTS

Seventy-seven participants (142 arms) were included, with 28 (19.7%) arms diagnosed with CuTS. The diagnostic performance of a 10 mm2 cutoff at ME and P2 showed high specificity, at 91.2% (95% CI 84.5-95.7) and 89.5% (95% CI 82.3-94.4), respectively. Sensitivity was below 40% at both sites. At D2 no CuTS cases met the 10 mm2 threshold. The highest diagnostic performance was observed at P2 level (AuROC 0.65, 95% CI 0.56-0.75), with an observable pattern of gradually decreasing nerve size proximally to distally, as demonstrated by the greatest proximal average CSA-U at P2, down to the smallest average at D2.

CONCLUSIONS

The CSA-U 10 mm2 cutoff value at both ME and P2 locations demonstrated high specificity despite limited sensitivity; therefore, it is suitable for ruling in CuTS diagnosis. The P2 location with a 10 mm2 cutoff appears to be a promising sonographic site for assessment. Ultrasonography may serve as a valuable adjunctive diagnostic tool in diagnosing CuTS in wheelchair users.

CLINICAL REHABILITATION IMPACT: Implementation of ultrasonographic CSA measurement at ME and P2 level could aid early detection of CuTS and enhance clinical decision-making due to greater accessibility at the outpatient clinic. Additionally, it also provides anatomical insights to electrodiagnostic evaluation.