Chapter 7:The Biomechanics of the Human Upper Extremity

Basic Biomechanics, 4th edition

Susan J. Hall

Presentation Created by

TK Koesterer, Ph.D., ATC

Humboldt State University

Objectives

• Explain how anatomical structure affects movement capabilities on upper extremity articulations.

• Identify factors influencing the relative mobility and stability of upper extremity movements

• Identify muscles that are active during specific upper extremity movements

• Describe the biomechanical contributions to common injuries of the upper extremity.

Structure of the Shoulder

• Most complex joint in body• Separate articulations:

– Sternoclavicular Joint– Acromioclavicular Joint– Coracoclavicular Joint– Glenohumeral Joint– Scapulothoracic Joint– Also: Bursae

Sternoclavicular Joint

• Provides major axis of rotation for movement of clavicle and scapula

• Freely permitted frontal and transverse plane motion.

• Allows some forward and backward sagittal plane rotation.

• Rotation

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

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:

– Joint capsule– Tendon of long head of biceps brachii– Glenohumeral ligaments

• Rotator Cuff• Rotator Cuff Muscles• Most stable in close-packed position, when the

humerus is abducted and laterally rotated.

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.

Bursae

• Small fibrous sacs that secrete synovial fluid internally to lessen friction between soft tissues around joints.

• Shoulder contains:– Subcoracoid bursa– Subscapularis bursa– Subacromial bursa

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

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

Muscles of the Scapula

• Functions:– 1) stabilize the scapula when shoulder

complex is loaded– 2) move and position the scapula to

facilitate movement at glenohumeral joint• Are:

– Levator scapula, rhomboids, serratus anterior, pectoralis minor, subclavius, and four parts to trapezius.

Muscles of Glenohumeral Joint

• Many muscles involved, some contribute more than others.

• Large ROM can complicate tension development with orientation of humerus.

• Tension development in one shoulder muscle is frequently accompanied by development of tension in an antagonist to prevent dislocation of the humeral head.

Flexion at Glenohumeral Joint

• Prime flexors:– Anterior deltoid– Pectoralis major: clavicular portion

• Assistant flexors:– Coracobrachialis– Biceps brachii: short head

Extension at Glenohumeral Joint

• Gravitational force is primary mover when shoulder extension isn’t resisted.– Control by eccentric contraction of flexors

• With resistance there is contraction of muscles posterior to the glenohumeral joint

• Assisted by:– Posterior deltoid– Biceps brachii: long head

Abduction at Glenohumeral Joint

• Major abductors of humerus:– Supraspinatus

• Initiates abduction• Active for first 110 degrees of abduction

– Middle deltoid• Active 90-180 degrees of abduction• Superior dislocating component

neutralized by infraspinatus, subscapularis, and teres minor

Adduction of Glenohumeral Joint

• Primary adductors:– Latissimus dorsi– Teres major– Sternocostal pectoralis

• Minor assistance:– Biceps brachii: short head– Triceps brachii: long head– Above 90 degrees- coracobrachialis and

subscapularis

Medial and Lateral Rotation of Humerus

• Due to action of:– Subscapularis

• Has greatest mechanical advantage for medial rotation

– Teres major• Assisted by:

– Primarily: pectoralis major– Also: anterior deltoid, latissimus dorsi and

short head of biceps brachii

Horizontal Adduction and Abduction at the

Glenohumeral Joint• Anterior to joint:

– Pectoralis major (both heads), anterior deltoid, coracobrachialis

– Assisted by short head of biceps brachi• Posterior to joint:

– Middle and posterior deltoid, infraspinatus, teres minor

– Assisted by teres major, latissimus dorsi

Loads on the Shoulder

• Arm segment moment arm:– Perpendicular distance between weight

vector and shoulder.• With elbow flexion, upper arm and

forearm/hand segments must be analyzed separately.

• 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

Rotational Injuries

• Tears of labrum– Mostly in anterior-superior region

• Tears of rotator cuff muscles– Primarily of supraspinatus

• Tears of biceps brachii tendon• Due to forceful rotational movements

– Also: calcification of soft tissues, degenerative changes in articular surfaces, bursitis

Structure of the Elbow

• Humeroulnar Joint

• Humeroradial Joint

• Proximal Radioulnar Joint

Segments at the Elbow

• Flexion and Extension– Muscles crossing anterior side of elbow are

the flexors:• Brachialis, biceps brachii, brachioradialis

– Muscles crossing posterior side of elbow are the extensors:• Triceps, anconeus muscle

Segments at the Elbow

• Pronation and Supination– Involves rotation of radius around ulna– Articulations:

• Proximal and distal radioulnar joints (both pivot joints)

• Middle radioulnar joint (syndesmosis)• Pronator quadratus• Supinator

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 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

Common Injuries to Elbow

• Sprains• Dislocations

– “nursemaid’s elbow” or “pulled elbow”• Overuse Injuries

– Lateral Epicondylitis = “tennis elbow”– Medial Epicondylitis = “Little Leaguer’s

Elbow”• Elbow injuries are more chronic than acute

Structure of the Wrist

• Radiocarpal joint– Reinforced by: volar radiocarpal, dorsal

radiocarpal, radial collateral and ulnar collateral ligaments

• Retinacula– Form protective passageways for tendons,

nerves and blood vessel to pass through

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)

Movements of the Hand

• CM Joints allow large ROM because similar to ball and socket joint– Digits 2-4 constrained by ligaments

• MP joints allow flexion, extension, abduction, adduction and circumduction for digits 2-5

• IP joints allow flexion and extension• Extrinsic Muscles• Intrinsic Muscles

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

Summary

• Shoulder is the most complex joint in the human body.

• Movements of the shoulder girdle contribute to optimal positioning of the glenohumeral joint for different humeral movements.

• Humeroulnar articulation controls flexion and extension at the elbow

• Pronation and supination of forearm occur at proximal and distal radioulnar joints.