Dooley Noted: 3/17/2016
Recently, I’ve experienced an influx of patients with both sternoclavicular (SC) joint and acromioclavicular (AC) joint dysfunctions.
The SC joint is a saddle joint and the only bony articulation to hold the upper extremity to the thorax.
The AC joint is a uniplanar (gliding) joint between the scapular and clavicular distal extremities.
These two joints are imperative for overhead movement of the shoulder girdle, relative to the thorax.
To best understand how their functions can be impaired, remember the muscles that attach to the clavicle:
1. Pectoralis Major
2. Trapezius
3. Deltoid
4. Subclavius
5. Sternocleidomastoid (SCM)
When considering actions of a muscle, remember that a muscle can only carry out powerful motion on one plane at a time.
When the sternum/ribs are fixed, the SC joint can be moved at the clavicle by the pectoralis major to aid in humeral flexion and horizontal humeral adduction.
If skull attachments stay fixed, the SCM can move the SC joint superiorly.
If the scapula is fixed, the deltoid moves the the clavicle to permit flexion and horizontal adduction, much like pectoralis major.
With the same bone fixed, the trapezius moves the clavicle superiorly to permit flexion and overhead movement.
If the first rib is fixed, the subclavius can pull the clavicle inferiorly, to work as a synergist to pectoralis major function.
So, the two-joint clavicle is more complicated than it looks, due to the importance of muscle coordination.
Assessment of shoulder pain must always start where all movement is anchored: at core stability.
After this assessment, SC and AC joint function must be assessed to see how the scapulothoracic and glenohumeral joints get their cues.
Assessing the shoulder without a huge focus on the clavicle will result in big misses in proper shoulder coordination.
After your core stability assessment, analyze these five muscles and their coordination with each other at the clavicular joints.
If you start treating rotator cuff before SC and AC joint, your treatments and correctives are unlikely to hold.
As always, it’s your call.
– Dr. Kathy Dooley