The scapula, commonly known as the shoulder blade, is a large, flat, triangular bone positioned on the upper back of the rib cage. It serves as the connection point between the upper arm bone and the collarbone, forming the shoulder girdle. Its triangular shape features three distinct edges, or borders, which provide specific anatomical landmarks for muscle origins and insertions.
Identifying the Scapular Borders
The three borders are named based on their position: the Superior Border, the Medial Border, and the Lateral Border. The Medial Border is often called the Vertebral Border because it runs nearly parallel to the vertebral column. This edge is the longest of the three, extending from the top corner to the bottom point of the bone.
Conversely, the Lateral Border is often called the Axillary Border because it faces the armpit, or axilla, and is directed toward the humerus, the upper arm bone. The shortest and thinnest is the Superior Border, which is located at the top and runs horizontally above the main body of the scapula. These three borders meet at the three corners, or angles, of the bone.
Distinctive Features of Each Edge
Each border possesses unique structural characteristics that relate directly to the muscles and neurovascular structures that interact with them. The Superior Border is notable for a distinct indentation called the scapular notch. This notch is covered by a ligament, forming a foramen through which the suprascapular nerve passes to reach the muscles of the shoulder.
The Medial Border provides a substantial area for the attachment of several large muscles responsible for scapular movement and posture. Muscles such as the rhomboid major and minor attach along the posterior side of this edge, helping to pull the shoulder blade toward the spine. The serratus anterior muscle attaches to the front surface of this border, anchoring the scapula to the rib cage and assisting in arm elevation.
The Lateral Border is the thickest and strongest of the three edges, offering a robust structure that supports the shoulder joint. This thickness is concentrated near the lateral angle of the scapula, where the glenoid cavity, the shallow socket for the arm bone, is located. The long head of the triceps brachii muscle, which extends the elbow, originates from a small bump just below the glenoid cavity along this border. The teres major muscle attaches along the lower portion of this Axillary Border.
Summary
The three borders of the scapula—the Superior Border, Medial (Vertebral) Border, and Lateral (Axillary) Border—outline the triangular structure of the shoulder blade. These edges are attachment points for the muscles that control arm and shoulder movement. Collectively, these anatomically distinct borders ensure the shoulder blade can move across the back while maintaining stability for upper limb function.