Biomechanics of the Hand SWAP 2006

Biomechanics of the Hand Swapnil Shah Dr. Markison March 6, 2006 Moment Arm Moment = Tension x Moment Arm Torque = Force x Lever Arm Mechanical Advantage = Distance moved by force/Distance moved by load Distance of force from axis/Distance of load from axis *Average Mechanical Advantage is 1:5 for each bone Moment Arm when force is not perpendicular to axis EFFICIENCY Measurable Variable Mass : Work Capacity Fiber Length : Excursion Potential Cross-Sec Area : Tension Potential Excursion Potential  Resting Fiber Length Required  Max Excursion in situ Available  Limited by soft tissue Discussion Points Thumb and Phalangeal Joints Extensor Mechanism: Relative Positioning Ratio of Moment Arm (FDP) largest at distal joint  Allows synchronized flexion Intrinsic Plus: Palmar Subluxation of MCP usage of intrinsic excursion and hyperextension of IP joint Intrinsic Paralysis: Grip Weakness, loss of opposition and cupping