Overview
This lecture covered the detailed anatomy of the shoulder as seen on MRI, focusing on bone landmarks, ligaments, labrum, joint capsule, and rotator cuff muscles, with tips on orientation and clinical relevance.
Bone Anatomy of the Shoulder
- The clavicle articulates with the acromion at the acromioclavicular (AC) joint.
- The acromion is part of the scapula, lying posteriorly, and is an important MRI landmark.
- The coracoid process projects anteriorly and is a crucial orientation marker.
- The glenoid fossa is a shallow socket on the scapula, articulating with the humeral head to form the glenohumeral joint.
- The humeral head should appear round and smooth, articulating with the glenoid.
Ligaments and Capsule
- Coracoclavicular ligaments attach the coracoid process to the clavicle.
- The coracoacromial ligament forms the roof of the coracoacromial arch.
- Glenohumeral ligaments (superior, middle, inferior) provide joint stability, especially anteriorly.
- The inferior glenohumeral ligament has anterior and posterior sections, visible on MRI.
Labrum and Common Injuries
- The labrum deepens the glenoid and provides stability; dark and well-defined on MRI.
- Anterior inferior labrum is a common site of Bankart lesions after dislocation.
- Observe for fluid entering the labrum, suggestive of tears.
Rotator Cuff Muscles and Tendons
- Supraspinatus runs above the scapular spine, attaches to the superior greater tuberosity, and is key in initial arm abduction.
- Subscapularis lies anterior, attaching to the lesser tuberosity.
- Infraspinatus and teres minor are posterior, attaching to the middle and lower greater tuberosity, providing posterior stability.
- The long head of the biceps tendon runs through the bicipital groove and attaches to the superior labrum (biceps anchor); short head attaches to the coracoid process.
MRI Orientation and Imaging Tips
- Use the coracoid process (anterior) and acromion (posterior) to orient MRI images.
- PD (proton density) images show both fat and fluid as bright; consider fat-saturated images to differentiate fluid from fat.
- Systematically assess bones, ligaments, capsule/labrum, and then muscles.
Key Terms & Definitions
- Glenoid fossa — shallow socket in the scapula for the humeral head.
- Labrum — fibrocartilaginous rim that deepens the glenoid.
- Rotator cuff — group of four muscles stabilizing the shoulder joint.
- Coracoid process — anterior bony projection from the scapula.
- Coracoacromial arch — superior arch formed by the coracoid, ligament, and acromion.
- Bicipital groove — channel on humerus for the long head of the biceps.
Action Items / Next Steps
- Practice identifying these structures using shoulder MRI scans.
- Review the anatomy of the shoulder with labeled diagrams for spatial understanding.
- Optional: Explore fat-saturated MRI images for distinguishing fluid from fat.