Relationship Between Ankle Plantar Flexion Angle and Tendon Gap in Achilles Tendon Rupture: A Prospective Study Using Portable Handheld Ultrasonography

Background Achilles tendon rupture (ATR) requires accurate diagnosis and timely intervention to reduce complications, disabilities, and costs. ATR gap influences treatment decisions, surgical or non-surgical. This study aimed to assess the correlation between ankle angle in knee flexion at 90 degrees and ATR gap size, exploring whether this method could reliably detect ATR and estimate the tendon gap. Methods In this prospective study, 47 patients with acute ATR underwent pre-operative assessment using portable handheld ultrasound. Measurements included the tendon gap at various foot positions and ankle angles in knee flexion. Baseline patient-reported outcome measures (PROMs) were also collected. Spearman's correlation was used to analyze relationships between gap size, angle measurements, and PROMs, while receiver operating characteristic (ROC) analysis identified an optimal ankle angle threshold. Results No significant correlation emerged between tendon gap size and angle values, nor between PROMs and angle or gap measurements. However, a significant difference in plantar flexion angles was found between injured and uninjured ankles, with a median of 99.4° for injured and 110.6° for healthy sides (p < 0.001). The optimal threshold of 104.75° achieved 83% sensitivity and 78% specificity in distinguishing ATR. Conclusion Ankle angle measurement may enhance ATR screening in settings without advanced imaging. The identified threshold could assist in clinical evaluation, though further research is needed to validate its use alongside portable handheld ultrasound as an accessible, cost-effective diagnostic tool.