Screw Angulation and Insertion Sequence Increase Interfragmentary Compression When Using Plates for Midfoot...

Area of Science:

• Orthopaedic biomechanics
• Surgical fixation techniques
• Bone healing research

Background:

• Achieving interfragmentary compression and stability is crucial for bone healing in fracture fixation and arthrodesis.
• Variable-angle screw designs in orthopaedic plating offer versatility, but screw trajectory's impact on compression and contact area requires further investigation.
• This study explored whether screw orientation forces align with vector geometry principles.

Purpose of the Study:

• To investigate the effect of screw trajectory on interfragmentary compression and contact area in bone fixation.
• To determine if screw orientation follows basic principles of vector geometry.
• To provide biomechanical insights for optimizing plate fixation techniques.

Main Methods:

• Foam bone surrogate osteotomy models were used to quantify interfragmentary compression and contact area with plates allowing 15 or 30 degrees of screw angulation.
• Screws were inserted at various angles in the surrogate models.
• Cadaveric second-tarsometatarsal (TMT) arthrodesis constructs were utilized to validate mechanical findings from surrogate testing.

Main Results:

• Interfragmentary compression and contact area increased with screw angulation (0 to 30 degrees) in surrogate models (ANOVA P < .001).
• Angling screws in the second bone fragment after plate fixation to the first yielded the greatest compression.
• In cadaveric TMT constructs, 30-degree screw divergence significantly increased compression (~15-fold) and contact area (~4-fold) compared to 0-degree divergence (P < .001).

Conclusions:

• Divergent screw placement in plate fixation improves interfragmentary compression and contact area, especially when angled into the second bone fragment after securing the plate to the first.
• The observed mechanical effects align with fundamental principles of vector geometry.
• Strategic screw angulation enhances fixation quality and stability, offering practical guidance for surgeons.