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Biomechanics of the Upper Extremity

KIN 311 - Berry College - Dept. of Kinesiology
by

David Elmer

on 1 April 2016

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Transcript of Biomechanics of the Upper Extremity

Biomechanics of the Upper Extremity
shoulder
elbow
wrist
humerus
clavicle
scapula
radius
ulna
sternoclavicular joint
major axis for movements involving the clavicle and scapula
shoulder elevation and swimming
close-packed position is in maximal shoulder elevation
acromioclavicular joint
very different from person to person
5 distinct types have been identified
movement at this joint occurs during arm abduction
close packed - 90 deg. of humerus abduction
glenohumoral joint
the most freely moving joint in the body
due to the humerus head having a much greater surface area than the glenoid fossa
egg-shaped
pear-shaped
45%
55%
labrum adds stability by adding depth to the fossa
rotator cuff aids stability by pulling humeral head toward glenoid fossa
close-packed - abducted, laterally rotated humerus
movement generalities:
scapulohumeral rhythm -
0 - 30 deg. elevation - mostly humeral movement, little scapular movement
after 30 deg. elevation - increased scapular movement
scapular muscles -
stabilize scapula, establishing a rigid base
help position the glenohumeral joint for effective movement
glenohumeral muscles -
muscle action changes based on position of humerus
antagonist activation is essential to prevent dislocation of the joint
flexion/extension
abduction/adduction
internal/external rotation
major flexors - anterior deltoid, pectoralis major
(clavicular portion)
extension -
- when unresisted, mostly just gravity
- when resisted - sternocostal pectoralis, latissimus dorsi, and teres major
major abductors -
supraspinatus and middle deltoid
0 - 110 deg
90 + deg
requires neutralizers
adduction -
unresisted = gravity
resisted - latissimus dorsi, teres major, sternocostal pectoralis
internal rotation -
primarily subscapularis and teres major
external rotation -
greater mechanical advantage
primarily infraspinatus and teres minor
horizontal ab/adduction
adduction -
muscles that attach are anterior to the joint
abduction -
muscles to the posterior of the joint
loads:
glenohumeral joint bears the greatest loads
arm - 5% of body weight, but long moment arm
injuries:
DISLOCATIONS:
glenohumeral - extremely mobile, also very unstable
usually occurs with abducted and externally rotated humerus
8-13% of all sports-related injuries
anterior dislocations most common
acromioclavicular dislocations (and clavicle fractures) from falling on rigidly outstretched arm
ROTATOR CUFF IMPINGEMENT:
forceful overhead movements with abduction/flexion and medial rotation
inflammation/rupture of rotator cuff tendons or bursae
ROTATIONAL INJURIES:
torn labrum, rotator cuff muscles, and biceps brachii
repeated forceful rotation of the shoulder
rotator cuff damage may be linked to low vascularity
SUBSCAPULAR NEUROPATHY:
due to rapid stretching of subscapular nerve during shoulder abduction and external rotation
humeroulnar joint
humeroradial joint
proximal radioulnar joint
hinge joint, flexion/extension, close-packed at full extension
gliding joint, close-packed at 90 deg flexion and 5 deg supination
pivot joint, with close-packed position at 5 deg supination
flexion/extension
flexion:
brachialis -
equally effective in pronated and supinated positions
biceps brachii -
more effective in a supinated position
brachioradialis -
most effective in neutral position
extension:
triceps and anconeus
70-90% of force
~15% of force
pronation/supination
proximal, middle, and distal radioulnar joints
pivot joints
syndesmosis
major pronator - pronator quadratus
major supinator - supinator
biceps brachii helps supinate when elbow is flexed >90 deg
compressive forces can exceed 400 lbs.
elbow extensors must generate more force to produce the same torque as the flexors
triceps moment arm is largest when elbow is fully extended and small when elbow flexed past 90 deg.
SPRAINS and DISLOCATIONS:
hyperextension of elbow
falling on outstretched arm
forceful, twisting blow
lots of nerves and blood vessels running in/through elbow...
OVERUSE INJURIES:
lateral epicondylitis - "tennis elbow"
inflammation of tissue on lateral or medial side of humerus, respectively
medial epicondylitis - "little leaguer's elbow"
valgus torque possibly to blame
intercarpal joints
radiocarpal joint
condyloid
close-packed - wrist extension and radial deviation
WRIST STRAINS and SPRAINS:
fairly common
falls higher than 0.6m can easily fracture the wrist
most common fracture in people under 75
CARPAL TUNNEL SYNDROME:
acute or chronic trauma compresses the median nerve, which runs through the carpal tunnel
results from repetitive, prolonged hand movement and wrist extension
wrist movements:
hand movements:
thumb movements:
Full transcript