Transcript Shoulder Lecture

Upper
Extremity
Shoulder Complex
Elbow
Wrist
(Hand)
1
Shoulder
Complex
sternoclavicular
acromioclavicular
coracoclavicular
scapulothoracic
glenohumeral
2
Shoulder
Girdle
• an “open” mechanical system
– R and L sides not directly
attached so can move
independently
• sternoclavicular jt
• acromioclavicular jt
• scapulothoracic jt
3
Sternoclavicular Articulation
• site of most movement of shoulder girdle
• articulation between the
sternum and clavicle
– elevation/depression (up and down, 30-40o)
• a modified ball-and-socket joint
o
– mobile in frontal and transverse
plane
– limited sagittal movement
– rotation (40-50 )
– protraction/retraction (A/P, rowing, 30o)
Interclavicular
Ligament
Clavicle
Sternoclavicular
Ligament
Costoclavicular
Ligament
Sternum
Clavicle
Articular
disk
Costal
cartilage
4
Acromioclavicular
Articulation
•articulation between
acromion process and
distal end of clavicle
coracoclavicular ligament
serves as axis of rotation for
associated scapular mvmts
very dense capsule +
AC ligaments
provide support
Bony Support -- WEAK!
5
AC Mvmts
3 df
protraction/retraction: acromion process
moves on meniscus, scapula rotates
about medial coracoclavicular ligament
(conoid) 30-50º
upward/downward rotation: clavicle
moves on meniscus, scapula rotates
about lateral coracoclavicular
ligament (trapezoid) 60º
elevation/depression: relative motion of
acromion & clavicle with no rotation
30º
Note: mvmts @ AC joint will be
opposite those at SC joint
(e.g., AC elevation -- SC depression)
6
Scapulothoracic Articulation
• “physiological” articulation (no bone-to-bone
connection) between the anterior surface of the
scapula (scapular fossa) and the thoracic wall
• scapula rests on 2 muscles (serratus anterior
and subscapularis)
• 60º ROM
7
Shoulder Joint
(aka glenohumeral)
- articulation of humerus and
glenoid fossa
- designed for mobility
(greatest ROM of any jt
in body)
- lacks bony and ligamentous
support
- shallow glenoid fossa
(1/4 size of humeral head)
-half-spherical humeral head
8
Supporting Structures for Shoulder
• labrum
– a lip of cartilage
surrounding the joint
– increases depth of fossa
– increases contact area
by 75%
– assists in holding the
humerus in place
9
coracohumeral
ligament
glenohumeral
ligaments
superior
middle
inferior
these ligaments
merge with the
articular capsule
10
Shoulder depends on ligamentous and muscular
contributions for support
articular capsule
2X volume of humeral
head - laxity
anterior support
capsule, labrum, glenohumeral
ligaments 3 “reinforcements” in
the capsule coracohumeral
ligament, and fibers of the
subscapularis and pec. major
that blend into the jt capsule
posterior support
capsule, labrum, fibers from
the teres minor &
infraspinatus that blend into
the capsule
11
Shoulder
Ligamentous Support
• no ligament to prevent backward displacement
– fossa angle slightly anterior
– prevents backward displacement
12
Subacromial Arch
coracoacromial
ligament
provides a “buffer”
for the rotator cuff
muscle tendons
13
Rotator Cuff Muscles
Infraspinatus
Supraspinatus
Subscapularis
3 originate
on posterior
scapula
(S I T)
Teres Minor
4th originates
on anterior
scapula
14
Stabilizing Influence of
Rotator Cuff
• muscles have a large
stabilizing component when
active
– all have a ‘large’ horizontal
component
– so play a significant role in
stabilizing the humerus
against the glenoid fossa
15
Bursae in Shoulder
• sacs secreting synovial fluid
• distributed throughout shoulder complex to
reduce friction between tissues
• e.g. subacromial bursae
– cushions rotator cuff muscles (supraspinatus) from
laying directly on acromion process
– overuse can lead to irritation of bursae
16
17
Abduction/Flexion
1) primary movers
2) humeral head stabilization
3) orienting the glenoid fossa
18
Abduction/Flexion
1) Primary movers
deltoid ~50%, rotator cuff ~50%
19
Abduction/Flexion
2) humeral head stabilization
early: teres minor depresses head
late: subscapularis & infraspinatus
stabilize head
>90º: supraspinatus remains active
20
Scapulohumeral Rhythm
•
scapular rotation to facilitate
shoulder movements (abduction &
flexion)
– 1st 30 º of abduction or 45º of
flexion -- scapula moves to a
position of stability on thorax
– beyond this initial range -- a
5:4 ratio of glenohumeral to
scapular movements
– for total ROM have a 2:1 ratio
(e.g. 180 º of abduction have
120 º of glenohumeral mvmt
and 60 º of scapular mvmt.
21
Abduction/Flexion
3) orienting the glenoid fossa
requires protraction, elevation, upward
rotation with posterior clavicular rotation
upper trapezius and serratus anterior
responsible muscles
22
Adduction & Extension
Primary Movers: If no resistance then use
eccentric actions of abduction/ flexion
muscles BUT if resistance (e.g. weight
machine or swimming) main contributors
are
latissumus dorsi
teres major
sternal portion of
pectoralis major
23
Adduction & Extension
Accompanying movements: retraction, depression,
downward rotation with anterior clavicular rotation
Rhomboid
downwardly rotates
& retracts
Pectoralis minor
depresses &
downwardly rotates
Mid & lower trapezius
retracts
24
Internal & External Rotation
Important to many sport skills plus a necessary
movement to accommodate mvmt when arm is at
90º or greater abduction or flexion
External rotation: infraspinatus & teres minor
primary muscles on posterior side
insert posteriorly on humerus
Internal rotation: subscapularis & teres major
primary muscles on anterior side
insert posteriorly on humerus
(also lat. Dorsi and pect. major)
25
Horizontal Ab-/Adduction
Similar musculature as for flexion and abduction
BUT more sig. contribution from
pec. major & ant. deltoid for hor. adduction
infraspinatus, teres minor, & pos. deltoid for hor. abduction
26
Muscular Strength
Shoulder Complex
adduction
extension
flexion
abduction
internal rotation
external rotation
STRONGEST
WEAKEST
27
Loads on Outstretched Arms
T = Fd
The moment arm(d) is the
perpendicular distance
from the line of action of the
weight to the axis of rotation.
C
B
if segment weight = 35 N
c
b
A
moment arms
a = 0 cm
b = 20 cm
c = 30 cm
shoulder torque
A. 0 N cm
B. 700 N cm
C. 1050 N cm
28
Shoulder Loading
• ergonomists recommend workers seated at desk
use arm position with 20 degrees or less of
abduction and 25 degrees or less of flexion
29
Shoulder Girdle Injury
• sternoclavicular joint
– low rate of injury
• sprain caused by force which displaces shoulder
anteriorly
• dislocation of medial end of clavicle medially, superiorly,
and either anterior or posterior
– posterior dislocation particularly dangerous because trachea,
esophagus, veins, etc. located behind
• dislocation in adults but usually fracture in children
30
Shoulder Girdle Injury
• acromioclavicular joint
– force applied laterally to acromion process
• commonly known as shoulder separation
• range from mild sprain of AC ligament to complete AC dislocation
with tearing of clavicular attachments of deltoid and trapezius &
complete rupture of coracoclavicular ligament
• displaces the acromion anteriorly and inferiorly while clavicle does
not move (95% of all dislocations for this joint)
• scenario - fall on an outstretched arm to break a fall
• force of impact transmitted through humerus such that entire
scapula is displaced relative to unmoved clavicle
31
Shoulder Injuries
• Dislocation or subluxation
– frequent due to lack of stability
– usually occur when shoulder abducted and externally rotated
• anterior-inferior dislocations most common (90%)
– when arm is abducted, extended, and externally rotated
• usually caused by a large external force
• age of 1st dislocation inversely related to rate of
recurrence
– i.e. the younger you are the more likely you are to have a
recurrence
32
Detecting a torn Rotator Cuff Tendon using an Arthrogram
Inject dye into joint to see if it leaks out where the rotator
cuff tendon is supposed to be
33
Detecting a torn Rotator Cuff Tendon using an MRI
34
Soft tissue injuries
Often associated with overarm motions
such as throwing
Preparatory phase -- shoulder
abducted to 90, shoulder ext
rotation, scapular retraction,
and elbow flexion
Anterior capsule and
subscapularis muscle are
susceptible to strain or tendinitis
at the insertion on the lesser
tubercle
35
Extreme External
Rotation in Overarm
Pitching
• external rotation
terminated by forces from
– anterior joint capsule &
ligaments
– subscapularis
– pectoralis major
– triceps brachii
– teres major
– latissimus dorsi
36
Acceleration Phase
• explosive phase
characterized by
– initiation of elbow extension
– shoulder internal rotation
– maintenance of shoulder
abduction at 90
– shoulder transverse adduction
– scapular protraction
• posterior capsule and labrum
susceptible to injury as
anterior shoulder is tightened
driving the humeral head
backwards
37
Follow-Through
Phase
• Rotator cuff works to
decelerate shoulder’s internal
rotation
• infraspinatus and teres minor
very susceptible to muscle
strain or tendinitis
38
Rotator Cuff Impingement
• impingement of
supraspinatus tendon
• 2 theories
– GENETIC: too narrow a space
between acromion and
humeral head
– OVERUSE: repeated
stretching of supraspinatus
weakens its ability to stabilize
the humerus leading to deltoid
pulling humerus up and
impingement of tissues
39
Swimmer’s Shoulder
• recovery
– near maximum tension in serratus anterior during
recovery to rotate scapula and facilitate overhead
arm movements
– fatigued serratus will not rotate scapula so rotator
cuff muscles impinged
40
Swimmer’s Shoulder
“Impingement Syndrome”
• @ hand entry
– shoulder forced into extreme abduction, flexion and internal rotation
– allows prox head of humerus to rub across the supraspinatus tendon
– can “impinge” the supraspinatus tendon between humerus and
coracoacromial ligament
– increased internal rotation when elbow is held in place and arm pushes
back
– head of humerus is thrust forward close to ligamentous structure of
shoulder joint where contact can occur
– increase likelihood of impingement
41
Swimmer’s Shoulder (cont.)
• at completion of arm pull
– shoulder adducted such that supraspinatus tendon is
stretched over the head of the humerus
– cuts off blood supply to tendon
42