The Biomechanics of the Human Upper Extremity

1. The Biomechanics of the Human Upper Extremity Dr Ayesha Basharat

3. Shoulder Girdle Includes: • G-H joint • Subacromial space • S-T joint • A-C joint • S-C joint

5. 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

6. Sternoclavicular Joint • Joint capsule • Anterior & posterior S-C ligaments • Intra-articular disc • Interclavicular ligament • Costoclavicular ligament

8. Sternoclavicular Joint • Protraction/retraction • Elevation/depression • Axial rotation (spin) Motions:

9. 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.

10. Acromioclavicular Joint • Joint capsule • A-C ligaments • Intra-articular disc • Coracoclavicular ligaments

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

13. 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.

14. Glenohumeral Motion • Passive restraints • Active restraints Controlled by:

15. Glenohumeral Motion • Bony geometry • Labrum • Capsuloligamentous structures • Negative intra-articular pressure Passive Restraints:

16. Capsuloligamentous Structures • SGHL • MGHL • IGHL complex • anterior band • posterior band • axillary pouch

17. Restraints to External Rotation • 00 - SGHL, C-H & subscapularis • 450 - SGHL & MGHL • 900 - anterior band IGHLC Dependent on arm position:

18. Restraints to Internal Rotation Dependent on arm position: • 00 - posterior band IGHLC • 450 - anterior & posterior band IGHLC • 900 - anterior & posterior band IGHLC

19. Restraints to Inferior Translation • 00 - SGHL & C-H • 900 - IGHLC Dependent on arm position:

20. 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.

21. 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

22. 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

24. 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

25. 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

26. 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.

27. Arm Abduction and Flexion

28. Muscle Action on the Shoulder Girdle

29. 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

30. 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

31. 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 symptom-limited function.

32. 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

33. Anterior dislocation

34. 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

35. Joint Capsule • Anterior • Posterior • Medial • Lateral • Large, loose and weak • Reinforced by other ligaments

36. 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

37. Wrist and Hand Bones • Wrist • Scaphoid • Lunate • Triquetrium • Pisiform • Trapezium • Trapezoid • Capitate • Hamate

38. Wrist and Hand Bones • Hand • Metacarpals • Phalanges 2-5 • Proximal • Middle • Distal • Phalange 1 (Thumb) • Proximal • Distal

39. Closer Look at the Carpal Tunnel • Structures within Tunnel • FDS • FDP • FPL • Median Nerve

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

41. Joint Structure of the Hand • Carpometacarpal (CM) • Metacarpophalangeal (MP) • Interphalangeal (IP)

42. 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

43. Swan neck deformity=== mallet finger • Boutonniere deformity

44. 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.