Locking Hole Inserts: Effect of Insertion Torque on Fatigue Performance and Insert Loosening in Locking Plates

Area of Science:

• Orthopedic biomechanics
• Implant material science
• Surgical innovation

Background:

• Bone fracture fixation relies on implants like locking plates.
• Plate fatigue life is critical for successful healing, especially in cases of delayed union.
• Locking hole inserts (LHIs) are a potential modification to enhance implant performance.

Purpose of the Study:

• To investigate the impact of locking hole inserts (LHIs) on the fatigue life of locking plates.
• To determine how varying insertion torque of LHIs affects plate fatigue performance.

Main Methods:

• Cyclic four-point bending tests were performed on 3.5-mm and 4.5-mm locking plates.
• Plates were tested with and without LHIs, with LHIs subjected to specific insertion torques (1.70 Nm and 3.96 Nm).
• The primary outcome measured was the number of cycles to plate failure.

Main Results:

• 3.5-mm plates with 1.70 Nm LHI insertion torque showed a 52% increase in fatigue life compared to controls (P=0.01).
• Increasing LHI insertion torque to 3.96 Nm resulted in a further 36% increase in fatigue life for 3.5-mm plates (P=0.02), and a 106% increase vs. controls (P=0.001).
• 4.5-mm plates with 3.96 Nm LHI insertion torque demonstrated a 48% increase in fatigue life (P=0.001).

Conclusions:

• Locking hole inserts (LHIs) significantly extend the fatigue life of locking plates.
• The use of LHIs is recommended in situations with potential for delayed fracture healing, particularly over bony gaps.
• Findings are specific to Smith & Nephew implants and highlight the biomechanical advantage of LHIs.