Shoulder complex biomechanics

angle of resting scapular plane

30-40 degrees

angle of resting clavicle

20 degrees

retroversion angle of humerus

30

what type of joint is the sternoclavicular

saddle

SC joint motions in the frontal plane

elevation (shrug) and depression

SC joint motions in transverse plane

protraction and retraction

SC joint motions in sagittal plane

anterior and posterior rotation (spin)

Arthrokinematics of SC elevation

superior roll and inferior glide

Arthrokinematics of SC depression

inferior roll and superior glide

Arthrokinematics of SC protraction

anterior roll and glide

Arthrokinematics of SC retraction

Posterior roll and glide

Arthrokinematics of SC during shoulder elevation

superior roll and inferior glide

w/ posterior rotation/spin

Arthrokinematics of SC during shoulder depression

inferior roll and superior glide

w/ anterior rotation/spin

Closed packed SC joint

full elevation with protraction

open packed SC joint

arm resting at the side

what type of movement does SC inferior accessory motion induce

elevation - pushing inferior causes posterior slide and superior roll

what type of joint is the AC

gliding joint

AC movement through transverse plane

internal/external rotation

AC movement through sagittal plane

anterior/posterior tilting

AC movement through frontal plane

upward/downward rotation

what biomechanical roles does the AC joint play

- maintains scapular congruency on thorax

- orient the glenoid fossa to improve joint congruency

- contributes to scapulothoracic motion: allows for rotational adjustments of the scapula

closed pack for AC

90 degrees shoulder abduction

open pack for AC

arm resting at side

kinematics of AC joint

subtle movement between scapula and clavicle

Sagittal plane motion and axis GH

flexion and extension, medial-lateral axis

transverse plane motion and axis GH

internal/external rotation, vertical axis rotation

frontal plane motion and axis

abduction/adduction, anterior-posterior axis

Abduction arthrokinematics

superior roll, inferior glide

adduction arthrokinematics

inferior roll, superior glide

flexion arthrokinematics

superior spin

extension arthrokinematics

inferior spin

internal rotation arthrokinematics

anterior roll, posterior glide

external rotation arthrokinematics

posterior roll, anterior glide

what direction would you want an accessory motion to be to improve shoulder abduction

superior to inferior

what direction would you want an accessory motion to be to improve internal rotation

anterior to posterior

what is the ratio of movement between the GH joint and the ST joint

for every 2 degrees the GH joint moves the ST joint moves 1 (2:1)

what allows for upward rotation of the scapula during shoudler elevation

SC and AC joints

how are degrees of motion divided between the SC and AC joint for shoulder elevation/abduction

evenly

how many degrees of motion are divided in the GH, SC, and AC joints if a patient gets 150 degrees of movement

GH - 100

AC - 25

SC - 25

what can't we elevate the arm completely when it is in extreme internal rotation

there is increased contact between the acromion and the greater tuberosity, external rotation allows the head of the humerus to clear the acromion and

ST joint elevation arthrokinematics

- elevation of clavicle

- AC: downward rotation

- SC: superior roll and inferior glide

ST joint depression arthrokinematics

- depression of clavicle

- AC: upward rotation

- SC: inferior roll and superior glide

ST joint protraction/abduction arthrokinematics

- protraction of clavicle

- AC: internal rotation

- SC: anterior roll and glide

ST joint retraction/adduction arthrokinematics

- retraction of clavicle

- AC: external rotation

- SC: posterior roll and glide

ST joint upward rotation arthrokinematics

- elevation of clavicle

- AC: upward rotation

- SC: superior roll, inferior glide, posterior spin

ST joint downward rotation arthrokinematics

- depression of clavicle

- AC: downward rotation

- SC: inferior roll, superior glide, anterior spin