What is the scapula and what does it do?
The body has 206 bones that make up the skeletal system at adulthood. Some of them are the stereotypical bone shape that you might think of if I asked you to picture a bone in the body. You might picture something like the long bone in the thigh, the femur. But there are also lots of bones in unique shapes that contribute to all the variability in movement that we can do. One of these unique bones is the scapula.
The scapula is one of the bones that makes up the shoulder complex. We have two of them—one on each side of the upper part of the back. Each bone is roughly triangular-shaped and is important for connecting the arm to the torso. The largest section of the bone is located posterior to the ribcage, but it also has two bony arms that curve around anteriorly and are part of the shoulder girdle.
Important bony landmarks on the scapula include:
- Coracoid process
- Spine of the scapula
- Superior angle
- Inferior angle
- Lateral border
- Medial border
- Supraspinous fossa
- Infraspinous fossa
- Glenoid cavity
The scapula bone is an important site for muscle attachment. There are 17 muscles that attach to it! These include the following:
- Serratus anterior
- Teres minor
- Teres major
- Rhomboids major
- Rhomboids minor
- Levator scapulae
- Pectoralis minor
- Triceps brachii
- Biceps brachii
- Latissimus dorsi
The scapulae connect with other bones at the:
- Acromioclavicular joint = where the acromion of the scapula meets the clavicle.
- Glenohumeral joint = where the humerus meets the glenoid fossa of the scapula.
- Scapulothoracic joint (a false joint) = although the scapula “floats” on the ribcage and does not connect with the ribcage in the way that we usually describe bones connecting at a joint, the area where the scapula meets the ribcage is sometimes referred to as the scapulothoracic joint.
Movements of the scapula
What does this curious bone do? The key task of our shoulders is to allow for the wide range of motion that we need to reach, grab, pull, and do all kinds of other things with our arms and hands. At the same time our shoulder girdle needs to be sufficiently stable to support that variety of movement. That's where the special shape of these bones comes in. Due to their shape, orientation, and the mobility of the joints where they meet other bones, the scapulae have a unique suite of possible movements. They include:
- Elevation = moves upward
- Depression = moves downward
- Retraction (also called adduction) = moves closer to the spine
- Protraction (also called abduction) = moves away from the spine and around toward the front of the ribcage
- Downward rotation = rotates around a central axis to bring the inferior angle closer to the spine
- Upward rotation = rotates around on its central axis to bring the inferior angle away from the spine
- Posterior tilt = the medial border lifts off the ribcage
The scapulae are unique bones in the body and contribute to the wide range of movements that we can access at the shoulder girdle. It's an important part of creating the balance between mobility and stability that is critical to functional movement at the shoulder girdle. If you’d like to learn more, check out our article on the shoulder girdle. For an even deeper dive, these resources from the National Library of Medicine are a great resource: https://www.ncbi.nlm.nih.gov/books/NBK531475/ and https://www.ncbi.nlm.nih.gov/books/NBK538319/