Background: RC pathology includes tendinopathy, partial- and full-thickness tears, and subacromial-subdeltoid bursitis, are a leading cause of shoulder pain and functional loss in active adults. HR-US is an easily accessible and dynamic imaging modality with the capability of conducting tendon-specific assessment with a high degree of accuracy. Nevertheless, variability in operator performance combined with patient positioning is a clinical limitation. Objectives: The aim of this study was to establish the diagnostic performance of HR-US as a first-line imaging modality in the diagnosis of RC pathologies and compare the accuracy with MRI using a standardized scanning protocol based on ESSR guidelines. Methods: In this retrospective cross-sectional study, a total of 283 patients aged between 20 and 65 years with complaints of shoulder pain, stiffness, or trauma were examined in several diagnostic centers in Sudan from 2021 to 2024. Examinations were performed using high-frequency linear transducers (7.5-12 MHz) on a unified HR-US protocol. MRI was used as a reference standard. Statistical analysis was made using SPSS, version 23, and diagnostic indices of sensitivity, specificity, accuracy, PPV, and NPV were calculated; p < 0.05 was considered significant. Results: HR-US obtained a sensitivity of 90.6%, specificity of 94.6%, for full-thickness tears, with an overall diagnostic accuracy of 92.6% and excellent correlation with MRI (r = 0.718, p < 0.001). The modality showed strong diagnostic performance for supraspinatus and infraspinatus lesions and proved superior to MRI in the detection of partial subscapularis tears in many cases. Standardized examination protocols greatly decreased inter-operator variability and improved reproducibility. Demographic analysis yielded strong associations of RC pathology with age and gender. Conclusion: HR-US is a reliable, accurate, and inexpensive first-line modality for diagnosing rotator cuff disorders. If performed in a standardized and tendon-specific protocol, HR-US diagnostic precision is comparable to MRI, while the former offers real-time dynamic assessment and is more accessible. It is worth integrating into routine diagnostic pathways, in particular in resource-constrained settings, for early diagnosis and evidence-based clinical decisions.