Dynamic pinch tolerance of the phalanges and interphalangeal joints

Area of Science:

• Biomechanics
• Orthopedic Trauma
• Human Factors Engineering

Background:

• Pinch injuries from moving surfaces are a common concern, particularly in automotive applications.
• Understanding the force and displacement tolerances of digits is crucial for injury prevention and safety design.

Purpose of the Study:

• To quantify the force and displacement tolerances of human digits (fingers and thumb) subjected to dynamic pinch loading.
• To establish safety guidelines for moving surfaces to prevent digit injuries.

Main Methods:

• Dynamic pinch loading (54 mm/s) was applied to cadaveric digits using aluminum pinching surfaces simulating automotive components.
• Injury was detected via acoustic sensors, and the applied force and surface gap distance at injury were recorded.

Main Results:

• Force tolerance varied from 245 N (little finger distal phalanx) to 1,155 N (index finger middle phalanx).
• Injury gap distances ranged from 4.5 mm to 9.1 mm, with a general trend towards larger gaps for proximal structures.
• Observed injuries included fractures (tuft, transverse, longitudinal) and tendon damage.

Conclusions:

• A gap of approximately 35% of the digit's dorsal-palmar dimension represents a critical tolerance threshold for pinch injuries.
• Moving surfaces with similar geometry are unlikely to cause digit injury if the gap remains above this 35% threshold.