Bones & Joints of the Shoulder Girdle: The Shoulder Girdle: Introduction
Some sources define the shoulder girdle as having two bones: the collarbone and shoulder blade. Some also include the humerus (upper arm bone).
Clavicle / Collarbone
- Located above first rib, running horizontally along the top of the chest at the base of the neck
- Long S-shaped bone
- Palpable along its entire length
- Connects arms to the trunk
- Keeps shoulder blades in place so the arms can hang freely
- The clavicle serves as an attachment for many muscles including the pec major, sternocleidomastoid, deltoid and trapezius (Physiopedia)
Scapula / Shoulder Blade
- Overlays the second through sixth or seventh ribs of the upper back
- Triangular-shaped flat bone
- Provides a stable base from which the shoulder joint moves the arm (JOSPT)
The Shoulder Joint / Glenohumeral (GH) Joint
- The shoulder joint is a synovial joint.
- It connects the upper arm bone to the shoulder blade.
- The head of the humerus (arm bone) forms the “ball” of the ball and socket shoulder joint.
- The glenoid cavity of the scapula (shoulder blade) is considered the “socket.”
- The shoulder joint is surrounded by connective tissue that is called a joint capsule. The joint capsule encases synovial fluid that lubricates the bones. It is also where ligaments and tendons insert.
- Three ligaments help stabilize the joint: the coracohumeral ligament, the transverse humeral ligament, and the coracoacromial ligament.
- While the head of the arm bone glides against the surface of the shoulder blade, “the steady contraction of the rotator cuff helps to hold the joint together.” (Doug Keller)
- Two bursae cushion the tendons and the bones of the joint.
- The joint permits a wide range of movements. (See Upper Arm Movements above.)
Acromioclavicular (AC) Joint
- A gliding synovial joint surrounded by a joint capsule
- Attaches the scapula (shoulder blade) to the clavicle (collarbone)
- The joint capsule and ligaments surrounding the joint work together to provide stability and to keep the collarbone in contact with the shoulder blade (Physiopedia)
- Allows for the scapula to tip and rotate internally and externally
- “Extremely susceptible to both trauma and degenerative change” (Physiopedia)
Sternoclavicular (SC) Joint
- A synovial joint surrounded by a joint capsule
- Connects the collarbone to the manubrium of the sternum
- The ligaments surrounding this joint are very strong, making dislocation of this joint unlikely
- This joint has the following motions available: elevation and depression of scapula, protraction and retraction of the scapula and axial rotation (i.e. when the arm is raised over head, clavicle rotates passively as scapula rotates) (Physiopedia)
- “The most common clinical presentation is pain and swelling… either after an injury to the shoulder, or insidiously, with no history of trauma” (Physiopedia)
These muscles are some of the primary stabilizing muscles, helping to connect the shoulder girdle to the rib cage and spine:
- Serratus Anterior
- Levator Scapulae
- Pectoralis Minor
- Latissimus Dorsi
The rotator cuff muscles are deep and wrap around the head of the humerus to connect and stabilize the arm bone in the shoulder socket. Other larger and stronger muscles are layered over the rotator cuff. These four muscles together are called the rotator cuff:
- Teres Minor