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Head-locking durability of fixed and variable angle locking screws under repetitive loading.

Mark Lenz1,2, Dieter Wahl1, Ivan Zderic1

  • 1AO Research Institute Davos, Clavadelerstrasse 8, CH-7270 Davos, Switzerland.

Journal of Orthopaedic Research : Official Publication of the Orthopaedic Research Society
|November 19, 2015
PubMed
Summary
This summary is machine-generated.

Polyaxial and fixed angle locking screws demonstrate durable head-locking mechanisms. Cyclic loading did not compromise screw stability, indicating reliable performance in fracture fixation.

Keywords:
fixed angle lockinglocking durabilitypolyaxial lockingscrew removal torquevariable angle locking

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Area of Science:

  • Orthopaedic biomechanics
  • Materials science in medical devices
  • Surgical fixation technologies

Background:

  • Polyaxial locking screws are increasingly used in fracture fixation.
  • The durability of their head-locking mechanism is critical for clinical success.

Purpose of the Study:

  • To evaluate the durability of the head-locking mechanism in variable angle (VA) and fixed angle (FA) locking screws.
  • To compare the removal torque of stainless steel and titanium locking screws before and after cyclic loading.

Main Methods:

  • Investigated removal torque of 2.4 mm stainless steel and titanium FA and VA locking screws.
  • Screws were subjected to cyclic loading (5 Hz, 25 N, up to 10,000 cycles) at various insertion angles.
  • Removal torque was measured before and after cyclic testing.

Main Results:

  • All screw types showed a decrease in removal torque after cyclic loading, but remained above 16% of initial values.
  • No instances of head loosening were observed in any group after cyclic testing.
  • Variable angle screws inserted at 15° showed lower removal torque compared to 0° and fixed angle screws.

Conclusions:

  • Both stainless steel and titanium 2.4 mm fixed and variable angle locking screws offer a stable and durable head-locking mechanism.
  • The locking mechanism remains effective even after significant cyclic loading, suggesting long-term stability in vivo.
  • Clinical application of these locking screws is supported by their demonstrated mechanical robustness.