Biomechanics Week 6: Shoulder

SCJ links

appendicular skeleton to axial skeleton

SCJ shape

saddle

Clavicle is convex

longitudinally

Clavicle is concave

transversely

Sternum is convex

transversely

Sternum is concave

longitudinally

SCJ Capsule

Anterior SC ligament

Posterior SC Ligament

Muscles of the SCJ

SCM

Sternothyroid

Sternohyoid

Subclavius

SCM stabilizes the SCJ

anteriorly

Sternothyroid & Sternohyoid stabilizes the SCJ

posteriorly

Subclavius stabilzes the SCJ

inferiorly

SCJ disc

Only fully formed in 50% of people

Acts as shock absorber

Sternoclavicular Joint ligaments

Anterior sternoclavicular ligament

Posterior sternoclavicular ligament

Interclavicular ligament

Costoclavicular ligament

Interclavicular ligament gets Taut when

clavicle depresses

Costoclavicular ligament stabilizes

all motions except for clavicular depression

Large forces through the clavicle, fractures

the bone before the SCJ dislocates

SCJ Osteokinematics

• elevation/depression

• protraction/retraction

• Axial (anterior/posterior) rotation

SCJ Elevation/Depression Osteokinematics

Frontal plane

A-P axis

SCJ protraction/retraction Osteokinematics

Horizontal plane about an vertical axis

SCJ Axial Rotation Osteokinematics

Sagittal plane about an M-L axis

SCJ elevation arthrokinematics

Convex clavicle rolls superior/medial and slides inferior/lateral on concavity of the sternum

Costoclavicular ligament becomes taut with

Clavicular elevation

Interclavicular ligament becomes slack with

Clavicular elevation

SCJ depression arthrokinematics

convex clavicle rolls inferiorly and slides superiorly

Costoclavicular ligament becomes slack with

clavicular depression

Interclavicular ligament becomes taut with

clavicular depression

SCJ protraction arthrokinematics

Concave clavicle Rolls and slides posterior

Anterior SCJ capsular ligament taut with

Protraction

Posterior SCJ capsular ligament slack with

Protraction

SCJ Axial Rotation Arthrokinematics

Spin because the axis pierces both partners of the joint

ACJ Disc

Only complete in 10% of people

Acromioclavicular joint type

Gliding or plane joint

Does the ACJ roll & slide

no! Does not follow Concave-Convex rule

ACJ movement follows

the scapula

ACJ Capsule

Superior and inferior ligaments

Acromioclavicular Joint ligaments

Acromioclavicular and Coracoclavicular

Coracoclavicular ligaments

trapezoid and conoid

Coracoclavicular ligaments function

suspends scapula from clavicle

If the Coracoclavicular ligament is torn

the scapula will sag from clavicle creating a step-off sign at the ACJ

ACJ kinematics

Movements described by movements of scapula relative to lateral end of clavicle

ACJ Osteokinematics

Up/down rotation

IR/ER

Anterior/Posterior tilting

ACJ upward rotation

Occurs with shoulder abduction

AC joint in shrugging

anterior tilt

ACJ downward rotation

Shoulder adduction and extension

Rotational adjustment motions

Fine tuning scap in horizontal and sagittal planes

(IR/ER about vertical axis; ant/post tilt on M-L axis)

Horizontal adjustments occur about a

Vertical axis

Sagittal adjustments occur about a

medial lateral axis

ACJ Anterior Tilt occurs when...

during elevation of the SCJ

AC joint posterior tilt

Acromion tilts posterior and inferior angle tilts anterior

Painful arc of motion 60-120º of shoulder

RTC or biceps pain

End range shoulder elevation pain =

more likely AC joint degeneration as source of pain

SCJ degrees of freedom

3

What ligaments restrict SCJ elevation

costoclavicular

What ligaments restrict SCJ depression

interclavicular ligament and the superior sternoclavicular ligament.

What ligaments restrict SCJ retraction

anterior Costoclavicular ligament and anterior capsular ligaments

Acromioclavicular Joint degrees of freedom

3

Scapulothoracic joint

not a true joint/pseudo joint

Contact point between scapula and posterior thorax

STJ

STJ separated by

Back muscles

Snapping scapula

scapula rubs over ribs

Can wear down interface between scapula and ribs

In anatomical position, scapula is between

2nd and 7th ribs

Avg resting posture of scapula

10º of anterior tilt

5-10 degrees of upward rotation

30-40 degrees of internal rotation

Plane of scapula

30 degrees anterior to the frontal plane

Scaption

Movement of the humerus away from the body in the scapular plane. Glenohumeral abduction in a plane 30 to 45 degrees between the sagittal and frontal planes

Scapulothoracic joint kinematics

elevation/depression

protraction/retraction

upward/downward rotation

Scapulothoracic joint kinematics: occurs with

cooperation of SCJ and ACJ

STJ elevation

clavicle elevation around SCJ + AC downward rotation

STJ elevation motion

shrugging shoulders

STJ Depression

clavicle depression + AC upward rotation

STJ depression motion

drop of shoulders

STJ protraction

clavicle protraction + AC IR

STJ protraction movement

Movement of scapula anteriorly like reaching forward

Scapula abducts

STJ Retraction motions

Movement of scapula posterior

Scapula adducts

STJ retraction

calvicle retraction

ACJ external rotation

STJ upward rotation

SCJ elevation

ACJ upward rotation

STJ elevation motion

Raising arm overhead

STJ downward rotation

SCJ depression

ACJ downward rotation

Anterior tilting of STJ

acromion tilts forward and inferior angle tilts backwards

Posterior tilting of STJ

acromion tilts posterior and inferior angle tilts anterior

Tilting of STJ motion occurs in

oblique medial lateral axis

Glenoid fossa and IR

Moves medially

Glenoid fossa and ER

goes postero laterally

Scapulothoracic Joint Kinematics

elevation/depression

protraction/retraction

anterior/posterior tilt

Plane of the scapula

30 degrees anterior to the frontal plane

What muscles control scapular elevation

trapezius, levator scapular, rhomboid

Scapular depression muscles

lower trapezius, pectoralis minor, serratus anterior, lats

What muscles control scapular protraction

serratus anterior, pectoralis minor

scapular retraction muscles

middle trapezius, rhomboids

scapular upward rotation muscles

upper trap, lower trap, serratus anterior

scapular downward rotation muscles

levator scapulae, rhomboids, pectoralis minor

scapula posterior tilt muscles

lower trap and serratus anterior

scapula anterior tilt muscles

serratus and pec minor

GHJ joint type

ball and socket

GH joint degrees of freedom

3 degrees

Gh joint formed by

glenoid fossa and convex humeral head

In anatomical position the glenoid is directed

anterolaterally in the scapular plane

Humeral head is directed medially, superiorly and posteriorly because of

retroversion

angle of inclination of the humerus

135 degrees

Angle of inclination gives

Gives humerus more Rom during overhead movements and keeps it in contact with glenoid

Humerus retroversion

Humerus is rotated 30 degrees posteriorly