The shoulder joint allows for an extensive range of motion. This complex structure connects the upper arm to the torso, enabling movements from lifting objects to intricate hand gestures. Its flexibility, however, comes with a trade-off, as this mobility can make it susceptible to injury. The shoulder achieves its broad capabilities through the coordinated action of several bones, muscles, and ligaments.
Anatomy of the Greater Tuberosity
The greater tuberosity is a prominent bony projection found on the humerus. Located on the upper, lateral, and posterior aspect of the humerus, it sits adjacent to the rounded head of the bone. This anatomical feature is easily palpable on the outer side of the shoulder, serving as a landmark.
This structure is characterized by its rough surface and distinct shape, which is important for its role in shoulder mechanics. The superior surface of the greater tuberosity is marked by three flattened impressions or facets. These facets provide specific areas for the attachment of tendons.
Inferiorly, the greater tuberosity extends into a ridge, the crest of the greater tuberosity. This crest, along with a similar ridge from the lesser tuberosity (another projection on the humerus), forms a groove called the intertubercular sulcus. The greater tuberosity’s position and structure are important to the overall architecture of the shoulder joint, acting as an anchor point for soft tissues.
Function in Shoulder Movement
The greater tuberosity serves as a direct attachment site for three of the four rotator cuff muscles: the supraspinatus, infraspinatus, and teres minor. Each originates from the scapula, or shoulder blade, and their tendons converge to insert onto the facets of the greater tuberosity.
The supraspinatus muscle, attaching to the superior facet, initiates abduction, lifting the arm away from the body. The infraspinatus and teres minor muscles, inserting onto the middle and inferior facets respectively, are primarily responsible for external rotation of the arm.
Collectively, these muscles, along with the subscapularis (which attaches to the lesser tuberosity), form the rotator cuff. This group is important for stabilization of the glenohumeral joint, ensuring the head of the humerus remains centered within the shallow shoulder socket during movements. Their combined strength allows for both powerful and precise arm movements, preventing unwanted displacement of the humerus.
Related Conditions
The greater tuberosity, due to its prominent location and role as a muscle attachment site, is susceptible to various injuries. Among the most common are fractures, which result from direct trauma, such as a fall onto the side of the shoulder, or when landing on an outstretched arm. These fractures can also accompany shoulder dislocations, where the force of the dislocation pulls a piece of the bone away.
A specific type of fracture is an avulsion fracture, where the strong pull of the attached rotator cuff tendons tears a piece of the greater tuberosity bone away from the humerus. These fractures can be either non-displaced, where the bone fragment remains in its proper position, or displaced. Displaced fractures are a concern because the attached muscles can pull the fragment further out of place, potentially leading to ongoing pain and limited shoulder movement if not managed properly.
Rotator cuff tears frequently involve tendons on the greater tuberosity. These tears can result from acute injuries, often related to the same traumatic events that cause fractures, or from gradual wear and tear. When a rotator cuff tendon, such as the supraspinatus, tears at its attachment point on the greater tuberosity, it can significantly impair the ability to lift or rotate the arm and cause pain.
Another related condition is shoulder impingement syndrome. Impingement occurs when the soft tissues, including the rotator cuff tendons and the bursa, compress in the narrow space beneath the acromion (the bony roof of the shoulder) during arm movements. The greater tuberosity, as it moves closer to the acromion during overhead activities, can contribute to this compression, leading to pain and inflammation.