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Ultrasonographic Evaluation of Zone II Partial Flexor Tendon Lacerations: a Cadaveric Study
Nikolas H Kazmers, MD, MSE; Joshua A Gordon, MD; Kristin Buterbaugh, MD; David R Steinberg, MD; David J. Bozentka, MD; Viviane Khoury, MD
University of Pennsylvania, Philadelphia, PA
Introduction: Identifying zone II partial flexor tendon lacerations is a clinical challenge. Based upon thresholds described in the literature (50-60%), determining the percentage of the tendon laceration may influence whether surgical repair versus observation are recommended. Validation of a noninvasive test that accurately identifies partial lacerations and determines the percentage of tendon involvement may reduce the need for exploratory surgery performed for diagnostic purposes. Our goal was to evaluate the ability of ultrasound to identify partial flexor tendon lacerations and determine their severity in a cadaveric model.
Materials & Methods: Flexor digitorum profundus (FDP) was exposed between A3 and A4 pulleys through midlateral incisions (32 digits, eight fresh-frozen above-elbow cadaveric specimens). Tendons were randomly selected to remain intact, or receive low- or high-grade lacerations (10-40% and 60-90% of the radioulnar width, respectively). Lacerations were randomly assigned to the radial or ulnar aspects of the tendon, and were localized with digital calipers and a keith needle prior to creating a sharp partial transaction in the transverse plane. Static and dynamic ultrasound was performed on the specimens with a linear-array 14 MHz transducer by a blinded fellowship-trained musculoskeletal radiologist (VK). Sensitivities, specificities, and other standard test performance metrics were calculated. Actual values and ultrasound measurements of the percentage of tendon laceration were compared using the paired t-test.
Results: Following randomization, 24 tendons were lacerated (12 low-grade and 12 high-grade) and 8 remained intact (Table 1). Sensitivity and specificity of ultrasonographic testing for presence versus absence of a partial laceration were 0.54 and 0.75, respectively, with likelihood positive (LR+) and negative (LR-) values of 2.17 and 0.61 (Table 2). For low-grade lacerations, sensitivity and specificity were 0.25 and 0.85, with LR+ and LR- values of 1.67 and 0.88, respectively. For high-grade lacerations, sensitivity and specificity were 0.83 and 0.85, with LR+ and LR- values of 5.56 and 0.20, respectively. Three (25%) of high-grade tears were misdiagnosed as low-grade. When considering lacerations accurately diagnosed as low- or high-grade, the percentage of tendon involvement was underestimated by ultrasound for low-grade lacerations (absolute difference -14.1%, p=0.03), but no different than actual values for high-grade lacerations (-6.7%, p=0.22). For lacerations that were detected, ultrasound correctly identified the side of laceration in 100% of specimens.
Conclusion: Ultrasound was useful in identifying and characterizing clinically-relevant high-grade zone II FDP partial lacerations in a cadaveric model. It was inaccurate in diagnosing low-grade lacerations. Validation in human subjects is required.
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