Joints of the Shoulder Girdle and Scapular Joint Actions

 

by Brent Brookbush DPT, PT, MS, PES, CES, CSCS, ACSM H/FS

What is a Joint:

• Joint: Where two or more bones meet.
  • Etymology: joint (n.) late 13c., “a part of a body where two bones meet and move in contact with one another,” from Old French joint “joint of the body” (12c.), from Latin iunctus “united, connected, associated,” past participle ofiungere “join” (see jugular). (Etymology Online)

• The naming of joints:
  • The names of joints are nothing to be intimidated by -no matter how long or complex the word may appear.  Joints are generally named by combining the names of the two bones or prominences in contact with one another. (The technical term for combed words is a portmanteau)Examples:
    • The shoulder is technically referred to as the glenohumeral joint – where the humerus meets the glenoid fossa of the scapula.
    • The knee is technically referred to as the tibiofemoral joint – where he tibia meets the femur meet

Joints of the Shoulder Girdle:

• The sternoclaviular joint – where the sternum meets the scapula meets the proximal end of the clavicle
  • Etymology:
    • Sternum -  “breastbone,” 1660s, from Greek sternon “chest, breast, breastbone” (in Homer, only of males), also “the breast as the seat of affections,” related to stornynai “to spread out,” from PIE *ster-no- “to stretch, extend,” from root *stere-, *ster- “to spread,” related to stornynai “to spread out” (see structure (n.)), on the notion of the chest as broad and flat, as opposed to the neck. Related: Sternal. (Etymology Dictionary)
    • Clavicle - Etymology: L, clavicula, little key (Medical Dictionary)

The Sternoclavicular (SC) Joint

• The acromioclavicular joint – where the acromion of the scapula meets the distal end of the clavicle
  • Etymology:
    • Acromio –  from the ancient greek roots Akron (peak) & Omos (Raw) (Medical Dictionary)

Acromioclavicular (AC) Joint

Joint Actions of the Shoulder Girdle:

As discussed in a previous lesson, Joint Actions describe motion occurring at joints.  Much like anatomical directions, these terms are specific language (jargon) used to communicate motion between professionals. Joint actions are specific to Planes of Motion and in most cases are labeled relative to the Anatomical Position.

Special Notes about Shoulder Girdle (Scapular) Motion:

• Although it may be referred to as the “scapulothoracic joint,” the scapula is not a true joint. There is no bony connection between the scapula and the thorax.  In fact, the only joint holding the arm, shoulder, scapula and clavicle to the thorax is the sternoclavicular joint.
• Shoulder girdle motion is a combination of motions that occur at the acromioclavicular joints (AC) and strernoclavicular (SC) joints respectively, and in lessons addressing Upper Body Dysfunction (UBD) we will find that the shoulder girdle motion is also affected by the motion of the ribs and thoracic spine. Most muscles affecting the shoulder girdle act on the scapula, so, rather than discussing the relatively complex relationship between the AC, SC, thoracic spine and ribs, it is common practice to refer to shoulder girdle motion by the resultant motion observed at the scapula.

Motion of the Shoulder Girdle = Motion of the Scapula

The scapula has its own set of joint actions:

The shoulder girdle has a set of joint actions specific to motion of the scapula.  Although this may seem like just another set of confusing terms to memorize, it is actually fortunate that we have a separate set of terms to use.  When we start analyzing scapulohumeral motion in later lessons it reduces confusion between the motion that is specific to the shoulder and the motion that is specific to the shoulder girdle (scapula).

Transverse Plane Joint Actions:

• Protraction – The scapula move away from the mid-line of the body and follow the curvature of the rib cage in lateral and anterior fashion.
• Retraction – The scapula move toward the mid-line of the body and follow the curvature of the rib cage in a medial and posterior fashion.

http://www.pt.ntu.edu

Frontal Plane Joint Actions:

• Elevation – The scapula move in a superior direction.
• Depression – The scapula move in an inferior direction.

http://www.pt.ntu.edu

• Upward Rotation– The inferior angle of the scapula moves in a superior-lateral direction such that the glenoid fossa faces upward.
• Downward Rotation – The inferior angle of the scapula moves in an inferior-medial direction such that the glenoid fossa faces downward.

http://www.pt.ntu.edu

Sagittal Plane Joint Actions

• Anterior Tipping – The superior portion of the scapula pivots anteriorly on the thorax
• Posterior Tipping – The superior portion of the scapula pivots anteriorly on the thorax

Note: Anterior Tipping and Posterior Tipping on the right hand side of the illustration.

Activity #1: Joint Actions, Planes and Sample Exercise

1. List the 8 joint actions discussed above (Note: Internal and External Rotation of the scapula not included in this lesson)
2. Identify the plane that each joint action occurs.
3. Choose an exercise that includes each joint action
4. The first row is completed as a sample

• Printable PDF of the Graph Below - Scapular Joint Actions and Exercises
• Answer Key - Scapular Joint Actions and Exercises Answer Key

Scapula-Thoracic “Joint”
Action	Plane	Exercise Example
Retraction	Transverse	Seated Rows/Pulling Movements