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Chapter 7: The Biomechanics of the Human Upper Extremity

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1 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

2 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.

3 Structure of the Shoulder
Most complex joint in body Separate articulations: Sternoclavicular Joint Acromioclavicular Joint Coracoclavicular Joint Glenohumeral Joint Scapulothoracic Joint Also: Bursae

4 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

5 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

6 Coracoclavicular Joint
A syndesmosis with coracoid process of scapula bound to the inferior clavicle by the coracoclavicular ligament. Permits little movement

7 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.

8 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.

9 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

10 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

11 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

12 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.

13 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.

14 Flexion at Glenohumeral Joint
Prime flexors: Anterior deltoid Pectoralis major: clavicular portion Assistant flexors: Coracobrachialis Biceps brachii: short head

15 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

16 Abduction at Glenohumeral Joint
Major abductors of humerus: Supraspinatus Initiates abduction Active for first 110 degrees of abduction Middle deltoid Active degrees of abduction Superior dislocating component neutralized by infraspinatus, subscapularis, and teres minor

17 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

18 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

19 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

20 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

21 Common Shoulder Injuries
Dislocations Rotator Cuff Damage Impingement Theory Subscapular Neuropathy Rotational Injuries

22 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

23 Structure of the Elbow Humeroulnar Joint Humeroradial Joint
Proximal Radioulnar Joint

24 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

25 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

26 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

27 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

28 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

29 Movements of the Wrist Sagittal and frontal plane movements
Rotary motion Flexion Extension and Hyperextension Radial Deviation Ulnar Deviation

30 Joint Structure of the Hand
Carpometacarpal (CM) Metacarpophalangeal (MP) Interphalangeal (IP)

31 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

32 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

33 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.

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