Mechanical behavior of screw versus Endobutton for coracoid bone-block fixation

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Shoulder reconstruction

Background:

• Arthroscopic coracoid bone-block fixation is an alternative to screw fixation.
• Complications associated with screw fixation necessitate evaluation of alternative methods.
• Limited comparative data exists on the mechanical properties of screw versus Endobutton fixation.

Purpose of the Study:

• To biomechanically assess and compare the fixation rigidity of screw versus Endobutton for coracoid bone-block.
• To test the hypothesis that Endobutton fixation exhibits lower rigidity than screw fixation.

Main Methods:

• Utilized 3D printed glenoid and coracoid models from patient CT scans.
• Implemented four fixation types: 1 or 2 malleolar screws, 1 or 2 Endobuttons.
• Performed lateromedial bone-block compression testing on a specialized bench, recording force and displacement.

Main Results:

• Screw fixation demonstrated significantly higher rigidity (158N/mm for 1 screw, 249N/mm for 2 screws) compared to Endobutton fixation (10N/mm for 1, 14N/mm for 2).
• Endobutton fixation resulted in greater bone-block displacement, particularly under superior or inferior forces.
• Using two Endobuttons reduced displacement compared to a single Endobutton, but overall rigidity remained substantially lower than with screws.

Conclusions:

• Screw fixation provides greater rigidity and stability for coracoid bone-block fixation.
• Endobutton fixation leads to increased bone-block mobilization, indicating potential mechanical vulnerability.
• While using two Endobuttons mitigates some displacement, screw fixation remains biomechanically superior until graft consolidation.