Relationship of scapular superomedial angle with acromion morphology

Aim: The effects of anatomical variations of the scapula on the health of shoulder girdle joints are still the subject of many studies. The level of association of acromion morphology with diseases such as rotator cuff tendinopathies and subacromial impingement syndrome, which cause the most shoulder pain complaints in patients, has been a subject of debate in recent years. It is seen that the scapular superomedial angle has been investigated only in relation with the snapping scapula syndrome to date. We planned this study to reveal the relationship between these two variations originating from the spina scapula in the developmental process and to determine a new criterion guiding the diagnosis. Materials and Methods: We analyzed 353 shoulder MRI scans performed in our hospital in May-June 2024 due to any complaint. We excluded patients with a history of previous surgery around the shoulder, masses in the shoulder girdle bones and surrounding tissues, and shoulder MR images that could not be properly evaluated due to technical errors during acquisition. Finally, the shoulder MR images of 4 patients with type 4 acromion were excluded from the study because they were not statistically significant and would increase the number of data and make it difficult to draw conclusions. Our study included 306 shoulder MR images obtained from 279 patients, 27 of which were bilateral. Of these images, 157 were of the right sjoulder and 149 were of the left shoulder. All MR images were obtained with a 1.5 T MRI device (Magnetom Aera, Siemens, Erlangen, Germany) using a standard (16-channel) shoulder coil. For acromion types, 3 groups were formed as type 1, type 2, and type 3; for superomedial angle, 2 groups were formed according to the values below and above the determined mean value. Subacromial space measurements in mm were recorded and evaluated without grouping. Rotator cuff, glenoid labrum, biceps brachii long head tendon were also examined by grouping them according to their intactness and pathologic status. Results: In acromion type 1 group, the median value of superomedial angle was 129 and the mean value was 128.4 ± 4.1; in type 2 group, the median value was 134 and the mean value was 133.7 ± 5.4; in type 3 group, the median value was 137 and the mean value was 137.4 ± 4.3. In our study, the significant efficacy of the superomedial angle in acromion types 1, 2 and 3 was shown with a p value of 0.000. Below the cut off value of 134° that we calculated for the superomedial angle, type 3 acromion is seen in 7.4% of scapulae, while type 1 acromion is seen in 1.3% of scapulae with a superomedial angle of 134° and above. Furthermore, the proportion 4 of normal rotator cuff was significantly (p<0.005) lower in the group with superomedial angle ≥ 134° (15.8%) than in the group with superomedial angle ≤ 133° (34.5%). Conclusions: This is the first study in the literature to show that the morphology of acromion changes with the superomedial angle, another structural differences of scapula. In particular, we can say that the incidence of type 1 acromion above 134° and type 3 acromion and related tendinopathies and subacromial impingement syndrome decreases below 134°. In this context, we have demonstrated that the superomedial angle is a parameter that can be used to evaluate glenohumeral joint and subacromial space pathologies as well as scapulothoracic pathologies. Key Words: Shoulder joint, scapula anatomy, acromion morphology, superomedial (costomedial) angle, subacromial space