Determination of the Cut-Off Value of the Acromiohumeral Center-Edge Angle on Shoulder Radiographs for Differentiating Partial-Thickness and Full-Thickness Supraspinatus Tendon Tears Based on MRI in Degenerative Rotator Cuff Tears

Abstract

Degenerative rotator cuff tear (DRCT) is a common cause of shoulder pain and functional impairment in middle-aged and older adults. The supraspinatus tendon is the most frequently affected component of the rotator cuff. Magnetic resonance imaging (MRI) is widely used as the reference standard for characterizing rotator cuff tears, including differentiation between partial-thickness and full-thickness tears. However, access to MRI may be limited by cost, availability, and waiting time. The Acromiohumeral Center-Edge Angle (ACEA) is a radiographic parameter that describes the geometric relationship between the acromion and the humeral head and has recently been associated with rotator cuff pathology. Nevertheless, the optimal ACEA threshold for differentiating partial-thickness from full-thickness supraspinatus tendon tears has not been clearly established.

To determine the optimal cut-off value of the ACEA measured on shoulder radiographs for differentiating partial-thickness from full-thickness supraspinatus tendon tears based on MRI findings in patients with degenerative rotator cuff tears.

This retrospective diagnostic study included 134 patients aged ≥40 years with degenerative supraspinatus tendon tears who underwent both shoulder radiography and MRI at Adam Malik General Hospital, Medan, Indonesia. ACEA was measured on standard shoulder radiographs and served as the index test, while MRI findings were used as the reference standard for classifying tears as partial-thickness or full-thickness. Differences in ACEA between groups were evaluated using an independent-samples t-test. Receiver operating characteristic (ROC) curve analysis was performed to determine the optimal cut-off value. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and diagnostic accuracy were calculated. Interobserver reliability was assessed using the intraclass correlation coefficient (ICC).

A total of 134 patients were analyzed. The mean age was 55.28 ± 8.84 years, with an age range of 40–82 years. Women comprised 70.9% of the study population. MRI demonstrated partial-thickness supraspinatus tears in 111 patients (82.8%) and full-thickness tears in 23 patients (17.2%). The overall mean ACEA was 31.85 ± 6.58°. The mean ACEA was significantly lower in the partial-thickness tear group than in the full-thickness tear group (29.87 ± 4.90° vs. 41.38 ± 5.19°, respectively; p < 0.001). ROC analysis demonstrated excellent discriminatory performance, with an area under the curve (AUC) of 0.948 (95% CI, 0.910–0.987; p < 0.001). The optimal ACEA cut-off was ≥34.92°, providing a sensitivity of 95.7%, specificity of 81.1%, PPV of 51.2%, NPV of 98.9%, and overall diagnostic accuracy of 83.6%. Interobserver reliability was excellent, with a single-measure ICC of 0.986 (95% CI, 0.975–0.992).

ACEA measured on shoulder radiographs was significantly higher in patients with full-thickness supraspinatus tendon tears than in those with partial-thickness tears. An ACEA threshold of ≥34.92° demonstrated excellent discrimination and a very high negative predictive value. ACEA may therefore serve as a practical complementary screening parameter for identifying patients who are more likely to have full-thickness supraspinatus tears and may benefit from further MRI evaluation, particularly in healthcare settings with limited MRI availability.