PAPER 28: ULTRASONIC WELDING OF BIOABSORBABLE PINS IN CANCELLOUS BONE FOR FRACTURE FIXATION

Abstract

Introduction: The SonicPin technology uses ultrasonic energy to weld polymer into bone (BoneWelding), thus forming a bond between implant and bone. The aim of this study was to determine the mechanical capabilities of the SonicPin in comparison to conventional techniques using generic mechanical load conditions.

Methods: Blocks of cancellous bone served as test specimens for generic tests. Two blocks respectively were fixed using either the SonicPin, a titanium cancellous bone screw (ASNIS) or a PLLA pin-screw system (Inion OTPS). The samples were then clamped into a test device and mechanically tested. Tests included pull-out, shear and 4-point-bending.

To examine the mechanical performance of the Son-icPin in a realistic fracture model 12 fresh frozen tibiae were osteotomized through the medial apex of the pla-fond, simulating a horizontal fracture of the medial malleolus. The tibiae were treated with either the Son-icPin or with 4.0-millimeter partially threaded titanium screws. Mechanical testing was performed by applying a compressive load 17 degrees from the long axis of the tibia to simulate supination-adduction loading.

Results: The bond between implant and bone exceeded the strength of the SonicPin itself. Using 2 SonicPins load levels were similar to those obtained with the cancellous screw or the PLLA fixation (p> 0,05).

Discussion: Ultrasonic welding of polymer into bone seems to be a promising technology to be used in orthopaedic surgery. Applying the SonicPin in fractures of the medial malleolus may be considered after slight modifications such as larger diameter or longer pins.