Biomechanics of the hand and wrist

Question 1

biomechanics of
MCP joint

Answer 1

Ellipsoid joint
Flexion, extension, abduction, adduction
Passive immobilisation: IP joint in extension and MCP joint in flexion so that collateral ligaments are taut, less prone to creating joint stiffness due to loss of tissue compliance

Question 2

Biomechanics of Thumb CMCJ

Answer 2

saddle joint, abduction, extension and pronation, flexion and adduction

Question 3

Biomechanics of
Interphalangeal joint

Answer 3

Simple single axis hinge joint
Flexion and extension
Static stability: collateral and accessory collateral ligament, volar plates
Rotational stability: trochlea and groove

Question 4

Quadriga effect in flexor mechanism

Answer 4

if one trendon of FDP is shortened, DIP of other fingers will exhibit a degree of flexor lag

FDP insert into distal phalanx after traversing through chiasma of FDS

Question 5

Intrinsic plus position and Intrinsic minus hand

Answer 5

Intrinsic plus: the MCP joints are flexed at 60-70°, the IP joints are fully extended, and the thumb is in the fist projection. The wrist is held in extension at 10° less than maximal

Intrinsic minus: Intrinsic Minus Hand is a hand deformity characterized by MCP joint hyperextension with PIP joint and DIP joint flexion caused by an imbalance between strong extrinsics and deficient intrinsics.

Question 6

Froment test

Answer 6

In ulna nerve palsy, adductor pollicis is denervated, in attempt to hold a sheet of paper between adducted thumb and index finger, thumb is pronated sufficiently for FPL (AIN) to perform lateral pinch

Question 7

What is Carpal instability

Answer 7

defined as an injury where there is a loss of normal alignment of the carpal bones and/ or the radioulnar joint.

Question 8

Four major types of carpal instability

Answer 8

Dorsiflexed intercalated segment instability (DISI): the lunate is an intercalated segment between the distal row and the abnormally extended forearm;

Volarflexed intercalated segment instability (VISI): the lunate appears abnormally flexed

Ulnar translocation: the proximal row has an ulnar deviation to the radius;

Dorsal translocation: the carpus is subluxed in a dorsal directions secondary to a fracture.

Question 9

Principle of tendon transfer

Answer 9

• The joint must be passively mobile.
• The gain in function must be greater than the potential loss.
• The motor must be of sufficient power (generally one MRC grade will be lost)
  and excursion.
• Ideally there should also be:
• one motor per joint to be moved; * a straight line of pull;
• synergistic transfers;
• sensibility of the recipient part.