Ultrasound Stress-Imaging is a Promising Tool to Detect Achilles Tendon Damage
Authors: O'Connor Kathryn , Schmidt Elaine , Hullfish Todd J. , Hast Michael W. , Baxter Josh R. 
Published: January 2022

Category: Sports; Basic Sciences/Biologics Introduction/Purpose: Achilles tendon disorders are among the most common conditions observed by sports medicine physicians and among the most difficult to diagnose using current clinical tools. While qualitative imaging is a validated method to grade the severity of tendinopathy, predicting the risk of these patients progressing or suffering tendon ruptures remains a major clinical need. Therefore, the purpose of this study was to determine the efficacy of quantitative ultrasound imaging to explain in vitro fatigue-induced degradation of Achilles tendon mechanical properties. We hypothesized that decreases in mean echogenicity would be linked to in vitro tendon fatigue characterized by decreased mechanical properties. Methods: In this cadaveric tendon study, we cyclically fatigued 10 cadaveric Achilles tendons (7 donors; sex: 4M, 3F; age: 60+-15 years) and acquired b-mode ultrasound images to determine if stress-imaging biomarkers provide new insight into tendon status. We cut dog-bone shapes to concentrate tendon damage at the mid-substance where we acquired ultrasound images. In a custom- built testing bath, we cyclically applied 10-20 MPa of tendon stress at 1 Hz for 150,00 or until the specimen failed. Every 500th cycle, we applied 2 slow (0.25 Hz) tendon stresses of 10-20 MPa while acquiring ultrasound images using an 18MHz transducer. We calculated the change in tendon echogenicity caused by the applied stress to determine if this stress-imaging biomarker was associated with tendon failure. We compared these stress-imaging biomarkers from the tendons that failed (N=6) and the tendons that survived (N=4) cyclic fatigue damage using an unpaired t-test (p < 0.05). Results: Quantitative analysis of the ultrasound images indicated 2 key differences between tendons that failed during the cyclic loading protocol and those that did not (Figure 1 shows representative data of tendons with similar demographics but one tendon exhibited increased change in echogenicity before failing while the other tendon exhibited smaller changes in echogenicity and did not rupture). First, mean echogenicity decreased before failure. Second, the average change in mean echogenicity was significantly greater in tendons that failed (p = 0.031). For most tendons that did fail, mean echogenicity decreased during the third phase of fatigue life. For the tendons that did not fail, mean echogenicity plateaued along with strain during the second phase of fatigue. Conclusion: This study found detectable differences in image echogenicity during a stress test between tendons that fail during cyclic loading and those that do not. While preliminary, our findings indicate that B-mode ultrasound has potential as a clinically viable tool to predict severe tendon injuries. Our future work is focused on developing computer-based predictive tools to assess Achilles tendon fatigue in patients with tendinopathy following prolonged tendon loading to establish quantitative imaging thresholds that can serve as clinical benchmarks.