Stiffness of modified Type 1a linear external skeletal fixators.

Area of Science:

• Orthopedic biomechanics
• Biomaterials engineering
• Surgical device innovation

Background:

• External skeletal fixators (ESFs) are crucial in orthopedic trauma management.
• Type 1a ESF frames offer a basic unilateral construct.
• Enhancing ESF frame stiffness is vital for improved fracture healing and stability.

Purpose of the Study:

• To evaluate the biomechanical stiffness of modified Type 1a external skeletal fixator (ESF) frames.
• To assess stiffness under axial compression (AC), cranial-caudal bending (CCB), and medial-lateral bending (MLB).
• To determine if modifications increase unilateral frame stiffness without proportional complexity.

Main Methods:

• Construction of nine, eight-pin frames for each design: Type 1a, Type 1a-MOD (modified pin placement), Type 1a-INSIDE, and Type 1a-OUTSIDE (additional rods).
• Utilized IMEX SK clamps, 3.2 mm pins, and 9.5 mm carbon fibre rods with Delrin bone models.
• Subjected constructs to repetitive, non-destructive loading (AC, CCB, MLB) using a materials testing machine.

Main Results:

• Type 1a-MOD and Type 1a-OUTSIDE constructs demonstrated significantly greater stiffness in CCB and AC compared to the standard Type 1a frame.
• All modified constructs (1a-MOD, 1a-INSIDE, 1a-OUTSIDE) exhibited significantly higher stiffness in MLB than the Type 1a frame.
• Stiffness was quantified in N/mm derived from load-deformation curve analysis.

Conclusions:

• Modifications to the Type 1a ESF frame can significantly enhance construct stiffness.
• The 1a-MOD and 1a-OUTSIDE designs offer improved biomechanical performance, particularly in bending and compression.
• These enhanced ESF designs hold potential for more stable fracture fixation without substantial increases in complexity.