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Ultrasound Measurement of Nerve Cross-Sectional Area: Evaluating Longitudinal Skill Retention
Kerilyn N Godbe, MD
1; Ellie Helton, BS
2; Niaman Nazir, MD, MPH
1; David Megee, MD
1; Charles C Jehle, M.D.
11University of Kansas Medical Center, Kansas City, KS; 2University of Kansas School of Medicine, Kansas City, KS
Background: Ultrasound (US) is an effective, user-dependent, tool for diagnosing carpal (CTS) and cubital (CuTS) tunnel syndromes. While US of the median nerve can be efficiently taught to trainees, this has yet to be demonstrated for the ulnar nerve. No studies have investigated longitudinal retention following one educational course.Methods: Fourteen integrated plastic surgery residents were assessed on their confidence (10-point scale) and ability performing diagnostic US for CTS and CuTS. Following a 10-minute instructional session, participants were re-assessed immediately, and again at 2-weeks and 1-month. Statistical analysis for continuous and discrete variables was performed via paired t-test and McNemar's or Chai-squared test, respectively. Results: Residents more often correctly identified the median (23.1% vs 92.3%; p=0.003) and ulnar (61.5% vs 84.6%; p=0.18) nerves following the teaching session. Post-teach, the median (0% vs 69.2%) and ulnar (15.4% vs 84.6%, p=0.003) nerves were more frequently identified in the correct location, with a significant increase in ulnar nerve measurement accuracy
(30.0 mm2 vs 3.0 mm2; p=0.03). Mean resident US confidence diagnosing CTS (1.9, SD 1.7 vs 5.6, SD 1.8; p<0.0001) and CuTS (1.6, SD 1.2 vs 5.3, SD 2.4; p=0.0002) significantly improved post-teach, and continued to rise at the two-week (CTS 6.6, SD 2; p=0.18: CuTS 6.6, SD 2.0; p=0.18) and 1-month (CTS 6.9, SD 3.3; p=0.54: CuTS 6.3, SD 2.5; p=0.54) timepoints. Despite increased confidence, there was no significant change between the proportion of residents on the post-teach who identified the correct structure or measured at the correct location, respectively, compared to the 2-week (CTS p=0.32, p=0.41; CuTS p=0.56, p=0.56) and 1-month (CTS p=1.0, p=1.0; CuTS p=0.32, p=0.56) timepoints. Of the residents who successfully measured the correct structure at the correct location, mean measurement accuracy (in mm2) progressively decreased between the post-teach, two-weeks, and one-month measurements, respectively (CTS: 1.0 [SD 1.0], 2.0 [SD 2.0], 3.0 [SD 3.0], p=0.17; CuTS 3.0 [SD 1.0], 3.0 [SD 4.0], 4.0 [SD 2.0], p=0.09). Despite being immediately post teach, 21.4% residents misdiagnosed a healthy model for both CTS (>10 mm2) and CuTS (>10 mm2). This proportion increased to 28.6% for both CTS and CuTS at one-month. Conclusions: US technique should be taught and used with frequency throughout residency if one expects it to be used accurately and efficiently. Those who do not frequently utilize US should carefully consider their comfort level prior to clinical utilization as nuances in technique prevent false positives and improper surgical intervention.
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