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14th Triennial Congress of the International Federation of Societies for Surgery of the Hand (IFSSH), 11th Triennial Congress of the International Federation of Societies for Hand Therapy (IFSHT)

17.06. - 21.06.2019, Berlin

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Ultrasound in carpal tunnel syndrome – the inlet and outlet ratio

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  • presenting/speaker Hirsiger Stefanie - Handchirurgie, Inselspital Bern, Bern, Switzerland
  • Esther Vögelin - Handchirurgie, Inselspital Bern, Bern, Switzerland

International Federation of Societies for Surgery of the Hand. International Federation of Societies for Hand Therapy. 14th Triennial Congress of the International Federation of Societies for Surgery of the Hand (IFSSH), 11th Triennial Congress of the International Federation of Societies for Hand Therapy (IFSHT), 11th Triennial Congress of the International Federation of Societies for Hand Therapy (IFSHT). Berlin, 17.-21.06.2019. Düsseldorf: German Medical Science GMS Publishing House; 2020. DocIFSSH19-1501

doi: 10.3205/19ifssh0546, urn:nbn:de:0183-19ifssh05463

Published: February 6, 2020

© 2020 Stefanie et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at http://creativecommons.org/licenses/by/4.0/.

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Objectives/Interrogation: Carpal tunnel syndrome is the most prevalent nerve compression syndrome in the upper extremity. To confirm median nerve compression, sonographical and electrophysiologic examinations have been described. The cross-sectional area (CSA) at the inlet and outlet of the carpal tunnel are used as diagnostic markers. As CSA of the median nerve varies with gender and occupation, a wrist-to-forearm-ratio has been proposed. As diagnostic sensitivity is still limited, the goal of this study was to retrospectively analyse CSA measurements and compare associated ratios.

Methods: 33 patients (44 wrists) diagnosed with CTS between 06/2016 and 08/2018 were included in the study. 23 were female, 10 male. Mean Age was 51 (range 21-89) years. Diagnosis was confirmed by nerve conduction studies. Measurements of CSA were performed using the continuous tracing method and a 17 or 18.5 MHz Linear Array Transducer (Philips iU22 Medical system or Philips 70 Affinity, Bothell, WA, USA). The absolute values of CSAForearm, CSAInlet, CSATunnel and CSAOutlet and the ratios CSAI/CSAF (Rforearm), CSAI/CSAT (Rpre) and CSAO/CSAT (Rpost) were compared. Data were analyzed using Excel (descriptive) and GraphPad for unpaired student t-test.

Results: Mean CSAF was 12.816 (SD 2.801), CSAI was 14.970 mm2 (SD 4.618), CSAT was 9.002mm2 (SD 2.664) and CSAO 13.798mm2 (SD 3.539). CSAF, CSAI and CSAO were significantly higher than CSAT (p< 0.0001). When referring to published cut-off values (>12.6 mm2 for CSAI and >13.2 for CSAO), only 29 (64.4%) respectively 22 (48.9%) of 45 pathologic wrists were identified. If using both CSA criteria combined, this number increased to 33 (75%).

Concerning ratios, Rforearm was in mean 1.195 (range 0.529-2.1), Rpre 1.761 (range 0.951-3.737) and Rpost 1.641 (range 0.778-5.132). When only analyzing the 11 wrists that would have been missed with the cut-off CSA values, mean ratios were 1.508 for Rpre, 1.611 for Rpost, and only 0.914 for Rforearm.

Conclusion: In these 33 patients, CSA values before and after the carpal tunnel were significantly higher than under the retinaculum. Nevertheless, 25% of pathologic wrists would have been missed if using absolute CSA reference values. If comparing the ratios, Rpre and Rpost had higher mean values compared to Rforearm, suggesting a higher sensitivity. These measures merit further evaluation in a prospective randomized study with a control group.