Biomechanical analysis of static forces in the thumb during hand function

Area of Science:

• Biomechanics
• Anatomy
• Orthopedics

Background:

• Understanding thumb joint and soft tissue forces is critical for diagnosing and treating hand injuries.
• Previous 2D analyses were insufficient for accurately determining static thumb forces.
• A 3D biomechanical model is needed to quantify internal forces during thumb function.

Purpose of the Study:

• To calculate internal forces in thumb joints and soft tissues during various pinch and grasp activities.
• To extend previous 2D analyses with a more comprehensive 3D approach.
• To provide quantitative data on tendon, muscle, ligament, and joint contact forces.

Main Methods:

• A 3D biomechanical model was developed, assigning mechanical equivalents to the thumb's anatomical structures.
• Joint orientation and tendon locations were determined using biplanar roentgenograms from cadaver specimens.
• Forces were calculated based on applied loads to the thumb tip during simulated pinch and grasp tasks.

Main Results:

• Thumb extrinsic and intrinsic tendons experienced forces up to 30 kg during pinch and 50 kg during grasp.
• Joint compression forces averaged 3 kg (interphalangeal), 5.4 kg (metacarpophalangeal), and 12 kg (carpometacarpal) during simple pinch.
• Carpometacarpal joint compression forces could reach 120 kg during strong grasp.

Conclusions:

• 3D analysis provides a more accurate method for calculating thumb joint and soft tissue forces.
• Significant forces are generated within the thumb's structures during common activities like pinch and grasp.
• These findings are essential for clinical applications in hand surgery and rehabilitation.