Biomechanics of wrist & Hand

Sagittal and frontal plane movements
Rotary motion
Flexion
Extension and Hyperextension
Radial Deviation
Ulnar Deviation

1. Biomechanics of wrist & Hand

2. Outline Introduction of hand Types of grasp Arches of the hand Functional position of the hand Joints of the hand Mechanism for finger flexion Mechanism for finger extension; the extensor mechanism Muscles that transmit force to the extensor mechanism How does the extensor mechanism work? Clinical appearance of peripheral nerve injuries in the hand Internet links related to the hand

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

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

5. Common Injuries of the Wrist and Hand Sprains and strains fairly common Metacarpal fractures and football Ulnar collateral ligament and hockey Wrist fracture and skate/snowboarding Wrist in non-dominant hand for golfers Carpal tunnel syndrome

6. Types of grasp Two types of grasp are differentiated according to the position and mobility of the thumb's CMC and MP joints. Power grasp Precision grasp

7. POWER GRASP (The adductor pollicis stabilizes an object against the palm; the hand's position is static.) cylindrical grip (fist grasp is a small diameter cylindrical grasp) spherical grip hook grip (MP extended with flattening of transverse arch; the person may or may include the thumb in this grasp) lateral prehension (this can be a power grip if the thumb is adducted, a precision grip if the thumb is abducted).

8. Prehension of hands

9. PRECISION ( Muscles are active that abduct or oppose the thumb; the hand's position is dynamic.) palmar prehension (pulp to pulp), includes 'chuck' or tripod grips tip-to-tip (with FDP active to maintain DIP flex) lateral prehension (pad-to-side; key grip)

10. Three arches balance stability and mobility in the hand. The proximal transverse arch is rigid, but the other two arches are flexible, and are maintained by activity in the hand's intrinsic muscles.

11. 1. PROXIMAL TRANSVERSE ARCH a stable bony arch that forms the posterior border of the carpal tunnel . The arch's integrity is maintained by a soft tissue "strut" formed by the flexor retinaculum or transverse carpal ligament (also called the volar carpal ligament). This ligamentous strut connects the scaphoid and trapezium on the arch's radial side with the hamate on its ulnar side, and forms the anterior border of the carpal tunnel.

12. 2. DISTAL TRANSVERSE ARCH It is also call metacarpal arch, because it is formed by the metacarpal heads; metacarpals 2 and 3 are stable while 4 and 5 are relatively mobile. You can observe the arch's combination of "radial" stability and "ulnar" mobility by loosely closing your fist, then squeezing more tightly, when you will observe movement in the more mobile fourth and fifth metacarpals.

13. 3. LONGITUDINAL ARCH Observe this arch's behavior as you loosely close your fist. The arches provide a balance between stability and mobility for grasping. For instance, we produce the so-called "chuck grasp" by using the more stable second and third metacarpals, instead of the more mobile fourth and fifth metacarpals. Therapeutic splints must support these three arches.

14. Functional position of the hand Wrist extended 20 degrees ulnarly deviated 10 degrees Digits 2 through 5 MP joints flexed 45degrees PIP joints flexed 30-45 degrees DIP joints flexed 10-20 degrees Thumb first CMC joint partially abducted and opposed MP joint flexed 10 degrees IP joint flexed 5 degrees

15. When therapists immobilize a patient's hand, they often position it this way. During a period of immobilization, the resting lengths of the hand's ligaments and muscles change. This hand position provides the best balance of resting length and force production so the hand can function when the patient mobilizes it again.

16. JOINT STRUCTURE AXIS MOTION CLOSE-PACKED POSITION Metacarpo-phalangeal (MP) biaxial (condylar) lateral A-P flexion/extension abduction/adduction first: extension 2nd-5th: flexion Proximal Interphalangeal (PIP) uniaxial lateral flexion/extension extension Distal Interphalangeal (DIP) uniaxial lateral flexion/extension extension Joints of the hand Joints of the hand

17. Mechanism for finger flexion FDP: flexor digitorum profundus (the deeper of the two) FDS: flexor digitorum superficialis (the more superficial muscle) Although the FDP is deep to the FDS over most of its course, it attaches to the skeleton more distally , because it passes through a 'split' in the FDS tendon.

18. Mechanism for finger extension We can extend the PIP and DIP joints without also extending the MP joints . But we can't extend the PIP joint without extending the DIP joint at the same time . Flexing only the DIP joint without also flexing the PIP joint is difficult . Full (active or passive) flexion of the PIP joint prevents active extension of the DIP joint.

19. Force Transmission • 80-90% through Radius & 10-20% - Ulna • Peak pressures are higher through Scaphoid fossa than lunate fossa • 50% of load applied through distal Carpus is transmitted through the Capitate to the scaphoid & lunate

20. Force Transmission Pattern of force transmittal depends on: • Wrist position • Capsuloligamentous integrity • Articular surface • Congruity

21. PERIPHERAL NERVE INJURIES IN THE HAND Median nerve: Often due to carpal tunnel syndrome. Wasting of thenar eminence Decreased thumb function, especially opposition. Thumb moves into plane of palm.

22. Ulnar nerve Damage to ulnar nerve can occur with trauma to elbow region. Ulnar neuropathy is a frequent complication of diabetes mellitus Wasting of web space and interosseous spaces . Affects strength of intrinsic muscles of hand, so person can't hold a piece of paper between extended but adducted fingers Affects adductor pollicis and ulnar head of FPB. A person who lacks strength in these muscles cannot grasp with the thumb unless he or she flexes the IP joint by substituting with the flexor pollicis longus.

23. Radial nerve injury Associated with gunshot or stab wounds, fracture of humerus , "Saturday night palsy ." person demonstrates a "dropped wrist," and cannot reposition thumb . lack of wrist extension may cause hand grip to be weak.

24. Thanks