hand biomechanics and basic functions

Mr Vaikunthan RajaratnamMBBS(Mal),AM(Mal),FRCS(Ed),FRCS(Glasg),FICS(USA),MBA(USA)

Dip Hand Surgery(Eur), Dip MEd(Dundee),MIDT Dist.(OUM)FHEA(UK),FFST(Ed),FAcadMEd(UK)

Senior Consultant Hand Surgeon

Hand Biomechanics and

Basic Functions

www.handsurgerymanual.com

vaikunthan@gmail.com

OER for this lecture

http://tinyurl.com/HandAnatomyFrom www.handsurgeryedu.com

Understanding Hand Surgery: A guide for junior doctors. (2008).

The hand extends from the fingertips to the pre & post-central gyri of the parietal lobe. It is an essential tool to interact with the environment. The presence of opposable thumbs has led the human race to build countless tools, from the pre-historic hunter-gatherers to a teenager ‘texting’ around the clock. It enables skilled workers to earn a living and is an instrument for written speech as well as non-verbal communication.

The signal change in human evolution was due to the upright gait.When man lifted his hands from the ground they were freed from the purpose of locomotion and were put into the service of

intelligence

Brain and Mind

• Cognition• Ego

•Memory• Senses & MotorTEMPORO PARIETEAL

LOBEHIPPOCAMPUS

PREFRONTAL CORTEX

DORSOLATERAL PREFRONTAL

CORTEX

Drivers for attention of the Brain

•Food•Fight •Flight and•Fornication

http://alieninthecaribbean.blogspot.sg/2011/10/2012-survival-kit-fear-and-fighting.html

The seat of learning • Area 4 the primary motor cortex, and

Area 6 immediately forward of Area 4• Area 6 the premotor area (PMA) +

signals of sensory components - guide the movements of the body

• Supplementary motor area (SMA), in the inner part of Area 6, -planning and execution of complex movements of both hands.

• This area together with the lower portion of the parietal lobe is where the mirror neuron system

Mirror neuron systems

• active during goal-directed action and while observing the same motor act

• meaning of a motor act (action understanding) is represented in this “mirror neuron system” (MNS).

• ability to observe and accurately imitate

• activated when an action is executed, observed, anticipated or imagined

• activated during kinaesthetic imagery

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Napier JR (1955) The form and function of the carpo-metacarpal joint of the thumb. J. Anat. 89, 362–369.

Prehensile function• thumb stability • full abduction or full adduction at CMC joint• articular surfaces congruent• Precision thumb fully abducted + stability by opposing another digit• Power thumb fully adducted

Young, R. W. (2003). Evolution of the human hand: the role of throwing and clubbing. Journal of Anatomy, 202(1), 165–174. https://doi.org/10.1046/j.1469-7580.2003.00144.x

anatomical reconstruction of the hand during human evolution - linked with tool behaviour

Throwing and Clubbing

Grasping a spheroid and precisely controlling itsrelease, required for accurate throwing, demands a gripthat differs from one that can firmly grasp a cylindricalclub-handle and absorb the reaction force of impactwithout release of the weapon

The balance of strength and robusticity has shifted radially,to the thumb, index and middle fingers

The flexor pollicis longus muscle, absent inchimpanzees, is the most powerful thumb muscle inhumans.

‘precision grip’ is a throwing grip‘power grip’ is a clubbing grip

Young, R. W. (2003). Evolution of the human hand: the role of throwing and clubbing. Journal of Anatomy, 202(1), 165–174.

Adaptations for throwing

•Grip the missile •Energy transmitted•Accurate release.

Requirements for throwing

• Fingertip grip• Mobile and long thumb • Opposable thumb pad to missile • Other finger pads to opposite side For accurate release:-• precise neural control• absorb the reactive propulsive thrust

‘… there are only two prehensileactions: these are called the precision grip and thepower grip’ (Napier, 1965).

• fingers rotate towards the central axis to meet the tip of the thumb

• Metacarpal hamate articulation - supination of the 4th & 5th MC

• heads 2nd & 3rd metacarpals - pronation of the proximal phalanges.

Stability 3rd metacarpal base – • dorsal styloid process preventing

hyperextension• Volar ligament - pisiform to the 3rd

metacarpal base

OER for this lecture

http://tinyurl.com/HandAnatomyFrom www.handsurgeryedu.com

vaikunthan@gmail.com