The humerus is the long bone that forms the upper arm, extending from the shoulder to the elbow. It serves as a crucial link, connecting the shoulder blade to the forearm bones. The proximal humerus, its upper end, plays a central role in shoulder joint mechanics, enabling a wide array of arm movements and daily activities.
Anatomy of the Proximal Humerus
The proximal humerus is the upper end of the humerus, located near the shoulder. This region articulates with the scapula, or shoulder blade, to form the shoulder joint.
The humeral head is a rounded, ball-shaped structure that fits into a shallow socket on the scapula called the glenoid cavity. Just below the humeral head is the anatomical neck, which separates the head from two bony projections: the greater and lesser tuberosities. The greater tuberosity is positioned on the lateral side, while the smaller lesser tuberosity is located more medially on the bone. These tuberosities serve as attachment points for muscles that control shoulder movement. Below these features lies the surgical neck, a narrower region frequently susceptible to fractures.
How it Functions in the Shoulder
The humeral head of the proximal humerus forms a ball-and-socket joint with the glenoid cavity of the scapula, creating the glenohumeral joint, which is the main articulation of the shoulder. This design allows for an extensive range of motion, making the shoulder the most mobile joint in the human body. Movements such as lifting the arm forward (flexion), moving it backward (extension), raising it away from the body (abduction), and rotating it are all possible due to this unique articulation.
Muscles and ligaments play a significant role in enabling these movements and providing stability to the shoulder. The rotator cuff muscles, a group of four muscles including the supraspinatus, infraspinatus, teres minor, and subscapularis, attach to the greater and lesser tuberosities of the proximal humerus. These muscles work together to rotate and lift the arm, while also holding the humeral head securely within the glenoid socket. Ligaments like the glenohumeral ligaments and coracohumeral ligament also connect the humerus to the scapula, reinforcing the joint capsule and contributing to shoulder stability during movement.
Common Issues with the Proximal Humerus
The proximal humerus is susceptible to common injuries and conditions. Fractures of the proximal humerus are among the most frequent upper extremity fractures, particularly in older adults, often resulting from falls onto an outstretched arm or direct trauma. These fractures are especially common in individuals with osteoporosis, a condition that weakens bones. The surgical neck is a common site for these breaks, but fractures can also occur at the humeral head or involve the greater and lesser tuberosities.
Beyond fractures, dislocations of the shoulder joint involve the humeral head coming out of the glenoid cavity. Rotator cuff tears are another common problem, where the tendons of the rotator cuff muscles, which attach to the tuberosities of the proximal humerus, are damaged. Such tears can result from acute injury or chronic wear and tear, and they can lead to pain and weakness, severely limiting the arm’s ability to move. Isolated fractures of the greater tuberosity, for instance, are often associated with rotator cuff injuries.