Aponeurotic expansion of the supraspinatus tendon: sonographic spectrum and proposed classifications.

Aim: The aponeurotic expansion of the supraspinatus tendon is a recognized but underappreciated anatomical structure of the shoulder. Its sonographic appearance may mimic or coexist with pathology of adjacent tendons, particularly the long head of the biceps tendon, creating diagnostic challenges. Although described in prior literature, many atypical variants remain insufficiently documented. This study aimed to characterize atypical sonographic manifestations of the aponeurotic expansion of the supraspinatus tendon and to propose new classifications based on its relationship with the supraspinatus tendon, its position within the rotator interval, and its association with the long head of the biceps tendon. Material and methods: Between October 2018 and September 2025, a total of 3,600 shoulder ultrasound examinations were performed. Nineteen patients (15 women, four men; mean age 60.7 years, range 24-82 years) with pathologically altered aponeurotic expansions were retrospectively identified. Each case was evaluated for structural and positional changes in relation to the supraspinatus, long head of the biceps, and subscapularis tendons. Results: The most frequent supraspinatus-aponeurotic expansion relationship was minor intrasubstance tearing (31.6%), followed by complete supraspinatus tears with retraction (21.1%). At the rotator interval, subluxation was observed in 36.8% of cases. Regarding interactions with the long head of the biceps tendon, aponeurotic expansion dislocation with preserved intragroove biceps alignment was most common (31.6%). Several theoretical subtypes were not observed. Conclusions: Ultrasound enables detailed assessment of the aponeurotic expansion of the supraspinatus tendon. The proposed classifications provide a structured framework for clinical practice and may guide future research into the diagnostic and functional significance of this complex region.