Optimal screw diameter for interference fixation in a bone tunnel: a porcine model

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Materials Science

Background:

• Securing tendon grafts in bone tunnels is crucial for successful reconstructive surgery.
• Interference screws are commonly used, but optimal dimensions for fixation strength are debated.

Purpose of the Study:

• To determine the optimal diameter of metal interference screws for securing tendon grafts in bone tunnels.
• To evaluate the effect of screw diameter on construct failure load and mode.

Main Methods:

• Porcine flexor tendon grafts (8 mm) were inserted into porcine distal femur bone tunnels (8 mm).
• Grafts were secured using 7 mm, 8 mm, or 9 mm diameter metal interference screws.
• Constructs were tested to failure using a universal material testing machine, recording load and failure mode.

Main Results:

• No significant difference in failure load between 7 mm and 8 mm screws.
• 9 mm screws exhibited significantly lower failure loads compared to both 7 mm and 8 mm screws.
• 9 mm screws led to 100% graft cutout failure; 7 mm screws primarily caused slippage; 8 mm screws showed mixed failure modes.

Conclusions:

• Interference screw diameters equal to or 1 mm less than the bone tunnel/tendon diameter provide superior fixation.
• Using a screw 1 mm larger than the tunnel diameter compromises fixation integrity and alters failure mechanisms.