Locking design affects the jamming of screws in locking plates
Sabrina Sandriesser1, Markus Rupp2, Markus Greinwald3
1Institute of Biomechanics, Trauma Centre Murnau, Murnau, Germany; Institute of Biomechanics, Paracelsus Medical University Salzburg, Salzburg, Austria.
Injury
|June 23, 2018
Summary
Screw seizing in locking plates is a clinical issue. The Thread & Conus locking mechanism reduces screw seizing compared to Thread Only designs, especially after cyclic loading and over-insertion.
Area of Science:
- Orthopedic surgery
- Biomaterials engineering
- Implant biomechanics
Background:
- Screw seizing is a common problem during the removal of locking compression plates (LCP) after fracture healing.
- This complication can hinder implant removal and potentially affect patient outcomes.
Purpose of the Study:
- To evaluate the impact of two distinct locking mechanisms on the incidence and severity of screw seizing in LCP systems.
- To compare the removal torque of screws subjected to different insertion torques and cyclic loading conditions.
Main Methods:
- Investigated 3.5-mm angular stable screws with two locking mechanisms: Thread & Conus and Thread Only.
- Screws were inserted at manufacturer-recommended torque or 150% increased torque (simulating over-insertion).
- Removal torques were measured directly after insertion and after a 100,000-cycle dynamic loading protocol.
Main Results:
- Screw seizing was confirmed by removal torques exceeding insertion torques across all conditions.
- The Thread Only design exhibited significantly more pronounced screw seizing (+37%) than the Thread & Conus design (+14%).
- Cyclic dynamic loading consistently increased screw seizing for both designs (P<0.0001).
Conclusions:
- Over-tightening and cyclic loading are significant contributors to screw seizing in locking plate implants.
- The Thread & Conus locking mechanism demonstrates a reduced tendency for screw seizing compared to the traditional Thread Only design.
- Clinical data supports the biomechanical findings, indicating the Thread & Conus design offers improved outcomes regarding screw removal.
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