Reproducibility of ultrasonographic measurements of the ulnar nerve at the cubital tunnel
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Objectives Ulnar nerve entrapment at the cubital tunnel is the second most common entrapment of the peripheral nerves of the upper extremities. Ultrasonography (US) is frequently used to ascertain the diagnosis and to evaluate tissue changes during and after treatment. However, reproducibility of US measurements of the ulnar nerve is incomplete. Therefore, the purpose of the current study was to determine the inter- and intra-rater reliability and the intra-rater agreement of US measurements of the cross-sectional area (CSA) of the ulnar nerve at the cubital tunnel in healthy adult subjects. Methods Throughout this test-retest study, two trained physical therapists, with three and seven years of US experience, determined the CSA of the ulnar nerve at the cubital tunnel. The CSA was obtained through a standardized protocol of the dominant arm of healthy participants. Two measurement sessions were performed per participant. Each session consisted of two measurements of the ulnar nerve per sonographer. The interval between the sessions was 15 minutes. Sonographers were blinded for their own as well as for each other’s outcomes. For statistical analysis the intraclass correlation coefficient (ICC) and the smallest detectable change were calculated. Results From March to April 2013, 69 participants (28 men and 41 women) with a mean ± SD age of 36 ± 15 years were included. Inter-rater reliability turned out to be fair to good with an ICC value of 0.63. The intra-rater reliability was excellent for both sonographers with an ICC of 0.85 for sonographer 1 and 0.88 for sonographer 2. The smallest detectable change of sonographer 1 and 2 were 2.47 mm2 (25% of the mean CSA) and 2.63 mm2 (26% of the mean CSA), respectively. Conclusion Owing to the fair to good inter-rater reliability, the excellent intra-rater reliability for both raters and the clinical applicable intra-rater agreement, US seems to be a valuable tool to assess the CSA of the ulnar nerve at the cubital tunnel for diagnostic and evaluative purposes in the physical therapy practice.