The Biomechanics of the
Human Upper Extremity
Dr Ayesha Basharat
Shoulder Girdle
Includes:
1. G-H joint
2. Subacromial space
3. S-T joint
4. A-C joint
5. S-C joint
Sternoclavicular Joint
 Provides major axis of
rotation for movement of
clavicle and scapula
 Freely permitted frontal
and transverse plane
motion.
 Close pack position is with
maximum shoulder
elevation
Sternoclavicular Joint
 Joint capsule
 Anterior &
posterior S-C
ligaments
 Intra-articular
disc
 Interclavicular
ligament
 Costoclavicular
ligament
Sternoclavicular Joint
Motions:
 Protraction/retraction
 Elevation/depression
 Axial rotation (spin)
Acromioclavicular Joint
 Irregular Diarthrodial joint
between the acromion process of
the scapula and the distal
clavicle.
 allows limited motions in all
three planes.
 Rotation occurs during arm elevation
 Close-packed position with
humerus abducted to 90 degrees
 In close- Packed position there is
maximum contact between the
articulating surfaces and stability is
also maximum.
Acromioclavicular Joint
 Joint capsule
 A-C ligaments
 Intra-articular disc
 Coracoclavicular
ligaments
Coracoclavicular Joint
 A syndesmosis with coracoid process of
scapula
 bound to the inferior clavicle by the
Coracoclavicular ligament.
 Permits little movement
Glenohumeral Joint
 Most freely moving joint in human body
 Glenoid Labrum composed of: fibrocartilage rim &
Joint capsule
Tendon of long head of biceps brachii
Glenohumeral ligaments
Rotator Cuff Muscles
 Most stable in close-packed position, when
the humerus is abducted and laterally rotated.
Glenohumeral Motion
Controlled by:
 Passive restraints
 Active restraints
Glenohumeral Motion
Passive Restraints:
 Bony geometry
 Labrum
 Capsuloligamentous
structures
 Negative intra-articular
pressure
Capsuloligamentous Structures
 SGHL
 MGHL
 IGHL complex
 anterior band
 posterior
band
 axillary
pouch
Restraints to External Rotation
Dependent on arm position:
 00 - SGHL, C-H &
subscapularis
 450 - SGHL & MGHL
 900 - anterior band
IGHLC
Restraints to Internal Rotation
Dependent on arm position:
 00 - posterior band
IGHLC
 450 - anterior &
posterior band IGHLC
 900 - anterior &
posterior band IGHLC
Restraints to Inferior Translation
Dependent on arm position:
 00 - SGHL & C-H
 900 - IGHLC
Scapulothoracic Joint
 Region between the anterior scapula and
thoracic wall.
 Functions of muscles attaching to scapula:
 Contract to stabilize shoulder region
 Facilitate movements of the upper
extremity through appropriate positioning
of the Glenohumeral joint.
Movements of the Shoulder Complex
 Humerus movement usually involves some
movement at all three shoulder joints
 Positioning further facilitated by motions of
spine
 Scapulohumeral Rhythm
Scapulohumeral Rhythm
 The ratio has considerable variation among individuals but
is commonly accepted to be 2:1 (2 of glenohumeral motion
to 1 of scapular rotation) overall motion.
 During the setting phase (0 to 30 abduction, 0 to 60
flexion), motion is primarily at the glenohumeral joint,
whereas the scapula seeks a stable position.
 During the mid-range of humeral motion, the scapula has
greater motion, approaching a 1:1 ratio with the humerus
 later in the range, the glenohumeral joint again dominates
the motion
Movements of the Shoulder Complex
 Muscles of the Scapula
 Muscles of the Glenohumeral Joint
 Flexion
 Extension
 Abduction
 Adduction
 Medial and Lateral Rotation of the Humerus
 Horizontal Adduction and Abduction at the
Glenohumeral Joint
Horizontal Adduction and Abduction at
the Glenohumeral Joint
 HORIZONTAL ADDUCTION: Anterior to joint:
 Pectoralis major (both heads), anterior deltoid,
Coracobrachialis
 Assisted by short head of biceps brachii
 HORIZONTAL ABDUCTION: Posterior to joint:
 Middle and posterior deltoid, infraspinatus, teres
minor
 Assisted by teres major, Latissimus dorsi
Loads on the Shoulder
 Shoulder joint has to bear most of the weight
amongst all other articulations of the shoulder girdle
 Shoulder has to provide direct mechanical support
 Large leverage
 More compressive forces on the shoulder joint
 Deltoid produces upward shear forces as compared
to rotator cuff which produces downward shear
forces.
Arm Abduction and Flexion
Muscle Action on the Shoulder
Girdle
Loads on the Shoulder
 Arm segment moment arm:
 Perpendicular distance between weight vector and
shoulder
 Large torques from extended moment arms
countered by shoulder muscles
 Load reduced by half with maximal elbow flexion
Common Shoulder Injuries
 Dislocations
 Rotator Cuff Damage
 Impingement Theory
 Subscapular Neuropathy
 Rotational Injuries
 Ectopic calcification
 Hardening of organic tissue through deposit
of calcium salts in areas away from the
normal sites
Subscapular Neuropathy
 The typical patient is a young overhead athlete who reports vague
posterior shoulder pain. Although, the athlete can have painless atropy
presenting as supraspinatus and/or infraspinatus weakness, depending
on the location of the suprascapular nerve.
 Because of the anatomy (see Functional Anatomy), more distal nerve
injuries are often relatively painless. In particular, nerve injuries at the
spinoglenoid notch that result in selective denervation of the
infraspinatus muscle may be painless condition..
 Based on anatomic considerations, athletes with more proximal lesions
of the suprascapular nerve that affect both the supraspinatus and
infraspinatus muscles are more likely to have pain and symptomlimited function.
Dislocations
 Loose structure of shoulder leads to extreme
mobility = less stability
 It may be Posterior, Anterior or inferior
dislocation
 Mechanism??////
 Contact sports
 Glenohumeral capsular laxity
 Strengthening of shoulder musculature
Elbow Articulations
 Humeroulnar Joint
 True elbow joint
 Strong bony configuration
 Hinge joint
 Humeroradial Joint
 Slides along capitulum
 Modified ball and socket joint
 Provides no ABD or ADD
 Proximal Radioulnar Joint
 Annular ligament
 Movements
 Interosseous membrane
Joint Capsule
 Anterior
 Posterior
 Medial
 Lateral
 Large, loose and weak
 Reinforced by other
ligaments
Loads on the Elbow
 Large loads generate by muscles that cross elbow
during forceful pitching/throwing
 Also in weight lifting, gymnastics
 Extensor moment arm shorter than flexor
moment arm
 Tricep attachment to ulna closer to elbow joint
center than those of the brachialis on ulna an
biceps on radius
 Moment arm also varies with position of elbow
Wrist and Hand Bones
 Wrist
 Scaphoid
 Lunate
 Triquetrium
 Pisiform
 Trapezium
 Trapezoid
 Capitate
 Hamate
Wrist and Hand Bones
 Hand
 Metacarpals
 Phalanges 2-5
 Proximal
 Middle
 Distal
 Phalange 1 (Thumb)
 Proximal
 Distal
Closer Look at the Carpal Tunnel
 Structures within Tunnel
 FDS
 FDP
 FPL
 Median Nerve
Movements of the Wrist
 Sagittal and frontal plane movements
 Rotary motion
 Flexion
 Extension and Hyperextension
 Radial Deviation
 Ulnar Deviation
Joint Structure of the Hand
 Carpometacarpal (CM)
 Metacarpophalangeal (MP)
 Interphalangeal (IP)
Common Injuries of the Wrist and Hand
 Sprains and strains fairly common, due to breaking a
fall on hyperextended wrist
 Certain injuries characteristic of sport type
 Metacarpal fractures and football
 Ulnar collateral ligament and hockey
 Wrist fracture and skate/snowboarding
 Wrist in non-dominant hand for golfers
 Carpal Tunnel Syndrome
 Swan neck deformity=== mallet finger
 Boutonniere deformity
Mallet finger
 In medicine, mallet finger, also baseball
finger,[1] dropped finger, dolphin finger, "Virgin
Finger", "Hannan Finger" and (more
generally) extensor tendon injury, is an injury of the
extensor digitorum tendon of the fingers at the distal
interphalangeal joint (DIP).[2] It results
fromhyperflexion of the extensor digitorum tendon, and
usually occurs when a ball (such as a softball,basketball,
or volleyball), while being caught, hits an outstretched
finger and jams it - creating a ruptured or stretched
extensor digitorum tendon.