MS (ORTHO), PDCC (HAND)
Unless our assessment of disability from functional
loss is anatomically accurate the necessary anatomical reconstruction to lessen
this disability cannot be precisely planned.
The hand should be regarded not only as an intricate
mechanical device but as a sensory area almost as important as the face in
communication.
The intact hand provides four functions.
a.
Subjective
sensory perception of the surrounding environment.
b.
Objective
sensory contact
c.
Communication
with others by direction and demonstration
d.
Mechanical
grips
1.
Power
grip
2.
Pinch
grip
3.
Static
grip
The radial digital tripod formed by the thumb, index
and middle fingers is so essential in pinch grip and manipulation. The sensory
supply is from the median nerve, which also supplies its extrinsic motors and
intrinsics (Lumbricals and flexor pollicis brevis). The medial digital hook
formed by ring and little fingers is provided by the ulnar nerve with both sensation,
extrinsic motor power and the hypothenar intrinsic function necessary for the
final torque of the power grip.
The thumb is essential for both power and position
grips.
As the hand approaches the objects to be picked up,
the extensor tendons posture the hand and fingers in preparation for the grip.
The long flexors then clamp the fingers against the palm with the thumb usually
in adduction.
The strength of this power grip in proportional to
the range of flexion in the smallest joints, so that any cause of
interphalangeal joint stiffness leads to serious weakening of the power
grip. The final torque of this power
grip in grasping objects comes from thenar and hypothenar intrinsics and the
loss of this transverse arch movement is noted in ulnar nerve palsy.
The little finger in contrast to its name little, is
mechanically very important in power grip as it adds to the breadth of the palm
and increases strength of power grip. Hence, decision in amputation of little
finger should be emphasized with caution.
The pinch grip depends on the intrinsic muscles for
posturing, stability and strength as loss of action of first dossal interosseus
weakens the radial abduction of the index against the thumb and loss of action
of adductor pollicis will break the longitudinal arch of the thumb, allowing
collapse under pinch grip stresses.
The opposition of the thumb against the stable index
and middle fingers indicates the significance of an intact median nerve supply
to provide discriminative sensation to these areas of contact, along with
thenar muscle innervation for effective opposition and precision manipulation.
The ‘backbone is fixed unit of the hand’ as littler
describes it is provided by second and third metacarpal shafts wedged into the
fixed distal carpal arch and motivated at the wrist by the two powerful wrist
extensors and flexor carpi radialis.
Sensation however is as important as motor power in
determining the function of a hand or of its parts.
Areas of functional contiguity have a common nerve
supply i.e., the radial digital tripod is supplied by median nerve. So also the
index, mid finger tips and ring, little finger tips touch their corresponding
areas of nerve supply over palm when they make a fist for power grip. This
improves the efficiency of the grip and the function.
All surgical reconstructions in the hand should be
planned on the basis of the above functional anatomy emphasizing the corollary
“NO HAND NO FUNCTION, NO FUNCTION NO HAND” in this era of functional
restoration.
Reference:
Ř Surgery of Repair as applied
to Hand Injuries by B.K RANK, A. R. WAKEFIELD and T.T. HUESTON
Ř Greens operative HAND
Surgery
DR.
BHARATH. K. KADADI
MS (ORTHO), PDCC (HAND)
CONSULTANT HAND SURGEON
HOSMAT HOSPITAL
BANGALORE