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Biomechanics of the Shoulder Complex - Coggle Diagram
Biomechanics of
the Shoulder Complex
Components of Shoulder Complex
3 osseous components of shoulder complex
include
Clavicle
Scapula
Humerus
function
Primarily designed for mobility but also
supports dynamic stabilization
The joints
Sternoclavicular (SC) joint
Acromioclavicular (AC) joint
Scapulothoracic (ST) joint
Glenohumeral (GH) joint
Sternoclavicular (SC) joint
Articular surfaces
consists of:
2 shallow saddle shaped surfaces
Located in the front of the complex on
the upper chest
1
at the medial end of the clavicle
-are incongruent. with little contact betw their articular surfaces
-The superior portion of the medial clavicle does not articulate with the manubrium
1 at the notch formed by the manubrium of sternum
and 1st coastal cartilage
Joint disc
has a fibrocartilage disc or meniscus
that incr congruence bet articuar surfaces
Upper portion of the disc is
attached to the
posterosuperior clavicle
Lower portion is attached to
the manubrium and
the first costal cartilage
Additionally attached to
the anterior and posterior
aspects of the fibrous sternoclavicular capsule
The disc transects
the joint space diagonally into
2 separate cavities
During shoulder motion
the disc act likes a hinge or a pivot
for the medial aspect of the clavicle
function
Provides stability
by incr joint congruence
absorbs forces
transmitted along the clavicle
frm its lateral end
to the sternoclavicular joint
Joint capsule and ligaments
is surrounded by a fairly strong fibrous capsule
but depends on 3 ligament complexes for the majority of it's support
Anterior and posterior sternoclavicular ligaments
(clavicle to the manubrium)
reinforce the capusule
& primarily function to check
anterior n posterior translatory movement
of the medial end of the clavicle
Bilaminar costoclavicular ligaments
(clavicle to the costal cartilages)
is a v strong lig betw clavicle n 1st rib
has 2 segments or laminae
Anterior lamina has fibers running
laterally from rib to clavicle
Posterior lamina has fibers running
medially from rib to clavicle
both Limit elevation of the lateral end of
the clavicle
Interclavicular ligament
(between clavicles)
Limits excessive depression
of the distal clavicle
& superior gliding of the
medial clavicle on the manubrium
the limitation of clavicular depression
by the interclavicular ligament is critical to
protecting structures such as the brachial plexus
& subclavian artery,
which pass under the clavicle & the 1st rib
sternoclavicular motinos
3 rotary degrees of freedom
Elevation/depression
and less than 15 degrees of clavicular depression
with depression, the lateral clavicle rotates downward
is a near-frontal plane movement
about a near– anterior-posterior axis of rotation(A-P axis)
allowing roughly upto 48 degrees of clavicular elevation
with elevation the lateral clavicle rotates upward
SC joint axis is described as lying lateral to
the joint at the costoclavicular ligament
Protraction/Retraction
occur in the transverse plane
about a vertical axis of rotation,(sueroinferior)
allowing about 15 to 20
degrees of protraction
lateral clavicle moves anteriorly
30 degrees or
more of clavicular retraction.
the lateral clavicle moves posteriorly
Axis lie at the costoclavicular ligament
Anterior/posterior rotation
anterior / posterior , or long axis rotation of the clavicle
During abduction or flexion of the shoulder,
the clavicle rotates posteriorly (around
50degrees) about its long axis.
As the shoulder is abducted, the
coracoclavicular ligament becomes taut
and spins the clavicle posteriorly.
The clavicle rotates anteriorly, back to its
rest position, as the shoulder is extended
or adducted.
the axis of rotation runs longitudinally thru the clavicle
intersecting the sternoclavicular n acromioclavicular joints
3 translatory degrees of freedom
Medial/lateral translation
Superior/inferior translation
Anterior/posterior translation
Saddle joint
motions of any joint are typically described by identifying the direction of movement of the portion of the lever that is furthest from the joint
sternoclavicular Stress
Although incroguent, it does not undergo the degree of degenerative change common to other joints
Strong force dissipating structures such as the SC disc and the costoclavilcular ligament minimizes articular stress and also prevents intra articular motion
Dislocation of the SC joint is only up to 1% when compared to the totality of the joint dislocations in the body and may account for 3% of the shoulder girdle dislocations