From the Research
The shoulder joint is a complex ball-and-socket joint with a wide range of motion, and its biomechanics involve the interaction of bones, muscles, tendons, and ligaments to allow for flexion, extension, abduction, adduction, and rotation, as described in the most recent study 1. The biomechanics of the glenohumeral joint depend on the interaction of both static and dynamic-stabilizing structures, including the bony anatomy, negative intra-articular pressure, the glenoid labrum, and the glenohumeral ligaments along with the joint capsule, as well as the rotator cuff muscles and other muscular structures surrounding the shoulder joint 2. Key components of shoulder biomechanics include:
- Glenohumeral joint: The main shoulder joint, where the head of the humerus articulates with the glenoid fossa of the scapula.
- Rotator cuff muscles: Supraspinatus, infraspinatus, teres minor, and subscapularis stabilize the joint and enable rotational movements.
- Scapulothoracic joint: The scapula's movement along the thoracic wall contributes to overall shoulder motion.
- Acromioclavicular and sternoclavicular joints: These joints allow for additional range of motion and stability.
- Force couples: Balanced muscle actions create smooth, coordinated movements. Understanding these biomechanics is crucial for diagnosing and treating shoulder injuries, as well as optimizing rehabilitation and performance, and can be informed by a thorough physical examination, including inspection, palpation, range of motion, strength, and neurovascular integrity 1. The overall ratio of scapulothoracic to glenohumeral movement of 1:2 is made possible by a clockwork mechanism that involves movements at these 2 articulations with axial rotation of the clavicle that connects the shoulder girdle to the torso, and stability of the scapulothoracic, glenohumeral joints and acromio clavicular joints rely not only on the intrinsic capsular ligaments, bony architecture and musculature, but also on extrinsic ligaments 3. Premature degeneration and tears of the rotator cuff tendons pose special clinical problems by disturbance of the delicate balance between the cuff and the deltoid muscle, highlighting the importance of proper biomechanical function in maintaining shoulder health 3.