Dr Ayesha Basharat

The Biomechanics of the Human Upper Extremity

Shoulder Girdle

1. G-H joint2. Subacromial space3. S-T joint4. A-C joint5. S-C joint

Includes:

Sternoclavicular JointProvides 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

Protraction/retraction Elevation/depression Axial rotation (spin)

Motions:

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 Coracoclavicul

ar ligaments

Coracoclavicular Joint

A syndesmosis with coracoid process of scapulabound to the inferior clavicle by the Coracoclavicular ligament.

Permits little movement

Glenohumeral JointMost freely moving joint in human bodyGlenoid Labrum composed of:

fibrocartilage rim &Joint capsuleTendon of long head of biceps brachiiGlenohumeral ligaments

Rotator Cuff MusclesMost stable in close-packed position, when the humerus is abducted and laterally rotated.

Glenohumeral Motion

Passive restraintsActive restraints

Controlled by:

Glenohumeral Motion

Bony geometry Labrum Capsuloligamen

tous structures Negative intra-

articular pressure

Passive Restraints:

Capsuloligamentous Structures

SGHL MGHL IGHL complex

anterior band

posterior band

axillary pouch

Restraints to External Rotation

00 - SGHL, C-H & subscapularis

450 - SGHL & MGHL

900 - anterior band IGHLC

Dependent on arm position:

Restraints to Internal Rotation

00 - posterior band IGHLC

450 - anterior & posterior band IGHLC

900 - anterior & posterior band IGHLC

Dependent on arm position:

Restraints to Inferior Translation

00 - SGHL & C-H

900 - IGHLC

Dependent on arm position:

Scapulothoracic JointRegion between the anterior scapula and thoracic wall.

Functions of muscles attaching to scapula:

Contract to stabilize shoulder regionFacilitate movements of the upper extremity through appropriate positioning of the Glenohumeral joint.

Movements of the Shoulder ComplexHumerus movement usually

involves some movement at all three shoulder joints

Positioning further facilitated by motions of spine

Scapulohumeral Rhythm

Scapulohumeral RhythmThe 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 ComplexMuscles of the ScapulaMuscles of the Glenohumeral Joint

FlexionExtensionAbductionAdduction

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, CoracobrachialisAssisted by short head of biceps brachii

HORIZONTAL ABDUCTION: Posterior to joint:Middle and posterior deltoid, infraspinatus,

teres minorAssisted by teres major, Latissimus dorsi

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 leverageMore compressive forces on the

shoulder jointDeltoid produces upward shear forces as

compared to rotator cuff which produces downward shear forces.

Loads on the Shoulder

Arm Abduction and Flexion

Muscle Action on the Shoulder Girdle

Loads on the ShoulderArm segment moment arm:

Perpendicular distance between weight vector and shoulder

Large torques from extended moment arms countered by shoulder musclesLoad reduced by half with maximal elbow flexion

Common Shoulder InjuriesDislocationsRotator Cuff Damage

Impingement TheorySubscapular NeuropathyRotational InjuriesEctopic calcification

Hardening of organic tissue through deposit of calcium salts in areas away from the normal sites

Subscapular NeuropathyThe 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 symptom-limited function.

DislocationsLoose structure of shoulder leads to

extreme mobility = less stabilityIt may be Posterior, Anterior or

inferior dislocationMechanism??////Contact sportsGlenohumeral capsular laxityStrengthening of shoulder

musculature

Elbow ArticulationsHumeroulnar Joint

True elbow jointStrong bony configurationHinge joint

Humeroradial JointSlides along capitulumModified ball and socket jointProvides no ABD or ADD

Proximal Radioulnar JointAnnular ligamentMovementsInterosseous membrane

Joint Capsule

AnteriorPosteriorMedial LateralLarge, loose and

weakReinforced by

other ligaments

Loads on the ElbowLarge loads generate by muscles that

cross elbow during forceful pitching/throwingAlso in weight lifting, gymnastics

Extensor moment arm shorter than flexor moment armTricep 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

WristScaphoidLunateTriquetriumPisiformTrapezium TrapezoidCapitateHamate

Wrist and Hand BonesHand

MetacarpalsPhalanges 2-5

ProximalMiddle Distal

Phalange 1 (Thumb) Proximal Distal

Closer Look at the Carpal Tunnel

Structures within TunnelFDSFDPFPLMedian Nerve

Movements of the WristSagittal and frontal plane movementsRotary motionFlexionExtension and HyperextensionRadial DeviationUlnar Deviation

Joint Structure of the HandCarpometacarpal (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 typeMetacarpal fractures and footballUlnar collateral ligament and hockeyWrist fracture and skate/snowboardingWrist 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.