Biomechanics Shoulder Flashcards
shoulder complex mobility/stability
greatest mobility of any joint
inherently unstable
how does the shoulder serve the hand through mobility and stability
mobility
-shoulder motion (w/ elbow) allows for infinite possibilities of hand positioning
stability
-must be capable of stability to maximize hand function
clavicle position
20 degrees posterior to frontal plane
10 degrees superior to transverse plane
what muscles attach to acromion
deltoid
lower/mid trap
glenoid fossa
- shape
- % surface area of humeral head
- what attaches around outside?
pear shaped
25% surface area
glenoid labrum attaches around bony rim
glenoid labrum
- function
- what attaches at superior glenoid
deepens glenoid
LHBT attaches at superior glenoid
SLAP lesion
- what is it?
- what population typically?
superior labral lesion
seen in overhead athletes
(superior labrum ant-post)
normal glenoid fossa orientation frontal plane
-when is the risk of should instability increased?
4 upward tilt
adult range
-7 downward tilt to 16 upward tilt
<5 superior tilt = increase in risk of shoulder instability
normal glenoid fossa orientation transverse plane
35 degrees anterior to frontal plane
humeral head angle of inclination
- range
- shoulder instability above what angle?
135
range: 130-135
shoulder instability above 140
humeral head angle of torsion
30-50 retroversion
shoulder complex joints
SC
AC
GH
scapulothoracic (not true joint)
movement of scapula on thorax controlled by motion at…
AC and SC joints
terms used to describe static postural scapular position
elevated/depressed protracted/retracted upwardly/downwardly rotated anteriorly/posteriorly tilted -involuntary; occurs to stay with thorax internally/externally rotated scapula
scapular winging is a consequence of what scapular position
IR
SC joint
- links shoulder complex to _____
- why does it have a paradoximal function?
axial skeleton
has to be stable, but mobile
SC joint
- type of joint
- -describe
synovial joint: saddle (modified) proximal clavicle -convex along long diameter -concave along transverse diameter stermum: reciprocal shapes
SC joint articular disc
- composition
- function
fibrocartilage functions -improves congruity -shock absorber separates SC joint into two joint cavities
SC joint connective tissues
joint capsule SC ligament costoclavicular ligament -limits all motions but depression interclavicular ligament -limits depression
SC stability assisted by what muscles
SCM
sternothyroid
sternohyoid
subclavius
SC joint degrees of freedom
3
- elevation/depression
- protraction/retraction
- axial rotation
clavicle elevation/depression (SC joint)
-available range
45 elevation
10 depression
clavicle elevation/depression arthrokinematics
- elevation roll and glide direction
- depression roll and glide direction
elevation
-superior roll, inferior glide
depression
-inferior roll, superior glide
clavicular protraction/retraction (SC joint)
- available range
- driver of what motion
range
-15-30 degrees each direction
drives of scapular pro/retraction
clavicular protraction/retraction arthrokinematics
retraction
-posterior roll and glide
protraction
-anterior roll and glide
clavicular axial rotation (SC joint)
-superior aspect of clavicle rotates _____ (direction and amount) with shoulder abduction or flexion
posterior 20-35 degrees
clavicular axial rotation arthrokinematics
spin of clavicle on sternum
mechanically linked with abduction/flexion of shoulder
AC joint connective tissues
- names
- which is primary stabilizer
- reinforced by…
joint capsule AC ligament coracoclavicular ligament -trapezoid portion -conoid portion -primary static stabilizer reinforced by -deltoid and trapezius attachments
AC motions
upward/downward rotation
-“frontal plane” but really scapular plane
anterior/posterior tipping
-sagittal plane
scapular int/ext rotation
-transverse plane
motions fine tune scapular position through subtle motions
scapular position (normal)
between ribs 2 and 7
medial border 6 cm from t-spine
10 degree anterior tilt
slight upward rotation
what occurs during scapular elevation
elevation of clavicle at SC
downward rotation at AC
fine tuning at AC
depression = opposite movments
what occurs during scapular protraction
protraction of clavicle at SC
horizontal plane adjustment at AC to keep scapula in contact with thorax
what occurs during scapular upward elevation
SC clavicular elevation
AC upward rotation
critical motion to allow normal raising of arm over head
GH joint capsule
- encloses…
- attachments
encloses GH joint -fibrous capsule -synovial capsule attachments -glenoid rim -anatomic neck
GH joint capsule
- how tight it is?
- what is the inferior portion called
loose fitting -allows for mobility inferior portion -axillary pouch -involved in frozen shoulder
RC tendons
- blend into…
- function
blend into capsule
when they contract, they tension capsule
creates dynamic tension in capsule
centers humeral head in glenoid
GH capsular ligaments (bands)
superior GH ligament
middle GH ligament
inferior GH ligament
review table 5-1, p. 139
inferior GH ligament portions
anterior
posterior
axillary pouch
other GH ligaments
-functions
coracohumeral ligament
-superior location
-tightens with ER, extension, and inferior humeral translation
transverse humeral ligament
-tethers long head of biceps tendon in bicipital groove
what provides GH stability with the arm at the side
SGHL and CHL -limit inferior and A/P translation -limit ER posterior capsule -limits posterior translation
what provides GH stability with arm in mid-elevation (45-60)
MGHL
-limits anterior translation and ER
posterior capsule
-limits posterior translation
what provides GH stability with arm above 90 elevation
IGHL anterior band -limits anterior translation and ER IGHL axillary pouch -limits inferior, anterior, and posterior translation IGHL posterior band -limits posterior translation and IR
GH capsuloligamentous complex summary
arm at side: superior capsule and ligaments are taught
as arm is elevated, gradual shift of ligamentous tension from superior capsule and ligaments to inferior capsule and ligaments
arm overhead: the “hammock” (IGHL) is primary static support
other GH non-contractile stability mechanisms
negative intra-articular pressure in joint creates relative vacuum
presence of intact glenoid labrum
-deepens socket
-suction cup effect
coracoacromial arch
- formed by
- structures in subacromial space
formed by acromion and CA ligament structures -LHBT -supraspinatus -superior capsule -subacromial bursa
bursae of shoulder
-location
subscapular
-extension of GH synovial capsule
-lies deep to subscapularis
subacromial
GH close-packed positioin
GH abduction and ER
GH loose-packed position
55 abduction
30 horizontal adduction
shoulder impingement
-caused by…
contact between humeral head against inferior acromion
scaption
- what
- benefit
abduction in scapular plane
better fit of humeral head in glenoid - less potential for pinching
why do you have less ER at the GH joint with the arm at the side compared to in 90 abduction
less motion due to coracohumeral ligament
GH IR/ER arthrokinematics
IR
-anterior roll, posterior glide
ER
-posterior roll, anterior glide
scapulohumeral rhythm purpose
distributes motion between multiple joints
maintains optimal glenoid position for stability
maintains effective muscle length-tension relationship
kinematic principles of should abduction (6)
180 shoulder complex abduction is result of 120 GH abduction and 60 ST upward rotation
60 ST upward rotation is result of SC elevation and AC upward rotation
clavicle retracts at SC during shoulder abduction
scapula posteriorly tilts and externally rotates at AC joint during shoulder abduction
clavicle posteriorly rotates at SC during abduction
GH externally rotates during abduction
scapulohumeral rhythm early phase
- what range is this?
- what occurs
initial 90 elevation
initial 30-50: setting
-minimal ST motion, most GH motion
-scapula is “seeking stability”
overall, 2 humeral elevation for each 1 of scapular motion
-30 ST upward rotation (20-25 SC elevation; 5-10 AC upward rotation)
-60 GH motion
scapulohumeral rhythm late phase
- what range is this
- what occurs
elevation above 90
2 humeral elevation of each 1 scapular motion
-30 upward rotation at ST joint (5 SC elevation; 25 AC upward rotation)
-60 GH motion
25 posterior rotation of clavicle as SC
posterior tilting and ER at AC
15 retraction of clavicle at SC
scapulohumeral rhythm summary
overall 180 elevation
-120 GH
-60 ST
early range: SC joint is greatest contributor to ST motion
late range: SC posterior rotation and AC upward rotation contribute to ST motion
possible contributors to abnormal shoulder kinematics
muscle fatigue: rotator cuff and periscapular muscles
muscle length issues (e.g. short pec minor)
abnormal T-spine posture/movmenet
intra-articular shoulder pathology
-adhesive capsulitis
-RC tear
-labral tear
for test, be able to answer following (review anatomy)
if _____ nerve is damaged, _____ muscle/movmeent might be affected
sensory supply to shoulder region
midcervical nerve roots (C3-C6) -SC: C3-4 -AC and GH: C5-6 peripheral nerves -axillary -suprascapular
elevators of ST joint
upper trap
levator scapulae
rhomboids
why might CN XI palsy lead to instability of GH joint
CH XI innervates UT
UT gives scapula its upward tilt
depressors of ST joint
lat
LT
pec minor
subclavius
CKC action of scapular depressors
can elevate the thorax
ST joint protractor
-why
serratus anterior
- long moment arm
- critical in shoulder complex function to properly position scapula
ST joint retractors
-co-contraction will…
middle trap
rhomboids
LT
con-contraction: neutralization of scapular rotation and elevation/depression
GH abductors
middle delt
supraspinatus
upper fibers of infraspinatus and subscap
shoulder flexors
anterior delt
coracobrachialis
LHBT
middle deltoid and supraspinatus
- explain relationship
- what occurs when one or both is paralyzed
similar moment arms
contribute = shares of total abductor torque
without deltoid: weak but full abduction
without supra: weak abduction and not full ROM
without both: no abduction
ST joint upward rotators
UT
LT
serratus anterior
UT, LT, and SA force couple
-explain
all three upwardly rotate
elevation/depression is neutralized
which part of the RC causes…
- superior roll
- inferior glide
- ER
- IR
superior roll -supraspinatus inferior glide -lower cuff ER -posterior cuff IR -anterior cuff
shoulder complex abduction muscles that... -move humerus -control scapular motion -control humeral head
move humerus -deltoid -supra control scapular motion -trap -SA control humeral head -RC
muscles that adduct and extend arm
-which shoulder girdle muscles participate in adduction/extension
posterior delt lat teres major LH triceps brachii pec major teres minor and infra downward rotators participate in adduction/extension
GH IR muscles
subscap pec major lat teres major larger muscle mass than ER greater torque
GH ER muscles
-function
infra
teres minor
posterior delt
decelerators of high velocity IR contractions
function of the following muscles for dynamic stability
- ST muscles
- RC
ST muscles
-critical for providing stable base for shoulder function and appropriately positioning scapula
RC
-co-contraction of RC is key
-creates dynamic stability
-compresses and centers humeral head in glenoid fossa
ideal shoulder profile during static observation
anterior -clavicle angle (10 upward) scapular position -between T2 and T7 -35 anterior to frontal plane -5-6 cm from midline thorax -flat against thorax -medial border relatively parallel to T-spine (NOT downwardly rotated) humeral head -<1/3 anterior to acromion -neutral rotation
