Locking Plates Advantages & Indications DJ 4213 1-11

Objectives Describe locking plates and how they differ in design from other bone plates Identify the advantages of locking plates over other plates Become familiar with the indications for use of locking plates DJ 4213

Locking Plates are an evolution. . . . . . of plate fixation DJ 4213

Plate Evolution DCP LC-DCP LCP Dynamic Compression Plate Limited Contact Dynamic Compression Plate LCP Locking Compression Plate DJ 4213

How is a Locking Plate Different? Conventional plates & screws depend on friction between the screw thread & bone for stability Locking plates & screws create fixed angles that do not rely on screw purchase in bone Conventional Screw & Plate Locked Screw & Plate DJ 4213

Conventional vs Locking Plates Again we see the initial stress in the bone due to tightening. When the bone is loaded along its axis, the bone around the screw is compressed on the load side of the fracture. As the load is increased, and the angle between the screw and the plate starts to change, the resultant loading vector on the screw changes from pure compression to a compressive and a tensile component. It is this additional tensile component which, when the elastic limit of the bone is exceeded, will cause toggling and eventual collapse across the fracture gap. The lock plate does not exhibit this behavior as the angles of the screws are fixed and there is no pre-load DJ 4213 5

When do Locking Plates Work Best? When conventional screw purchase may be poor: Osteopenic bone Metaphyseal areas Periprosthetic fractures Failed fixation/nonunion Screw strippage DJ 4213

Plate Design Looks familiar: Same basic construct of plates and screws Anatomically shaped Same stainless steel and titanium materials DJ 4213

Plate Design: Combination Hole “Figure of eight” hole design Locking screws Conventional cortex & cancellous screws DJ 4213

Locking Screw Design Threaded underside of head Larger core diameter: To thread (lock) into plate hole Larger core diameter: Increases strength Dissipates load over larger area of bone Smaller thread pitch: Threads not used to generate screw thread purchase in bone 4.5mm Cortex screw has a 3.2mm core diameter 4.0mm Locking screw has a 3.4mm core diameter 5.0mm Locking screw has a 4.4mm core diameter 3.5mm Cortex screw has a 2.5mm core diameter 3.5mm Locking screw has a 2.9mm core diameter Locking Screw Cortex Screw DJ 4213

Locking Screw Design Core design: Solid and cannulated Cannulated screws are inserted over guide wires for precise placement DJ 4213

Screw Head Designs Threaded head: Conical head: Locks screw to plate Conical head: Can be used before, or instead of, locking screws Partially threaded -- lags two fragments together Fully threaded -- pulls bone to plate Spherical head cortex screw: Conventional use DJ 4213

Locking Plates and Screws How do locking screws affect the surgical technique? DJ 4213

Conventional Plate Fixation Loss of Reduction Pre Reduced Fracture DJ 4213 8

Conventional Plate Fixation DJ 4213

Locking Plates & Screws No Bone Alignment to the Plate Non Reduced Fracture DJ 4213

Locking Plates & Screws No Fracture Malalignment Pre Reduced Fracture DJ 4213

Variable Angle Plates New in locking plate technology Allows screws to be angled around central axis of plate hole to match anatomy First seen in distal radius plates DJ 4213

Variable Angle Plates Now part of new Forefoot-Midfoot System Will be seen in large & small fragment periarticular plates DJ 4213

Variable Angle Plates VA holes require special drill guides & VA Locking Screws Spherical rather than straight head Be careful – look similar Variable Angle locking screw Standard locking screw DJ 4213

Locking Plates and Screws Technique Requirements: Reduction essential first Lag before you lock DJ 4213

Original AO Principles Anatomic reduction Stable fixation Preservation of blood supply Early motion Do the AO Principles still apply? DJ 4213

Locking Plates & Screws AO Principles 1) Anatomic Reduction: Locked plate design allows lag screw and compression plating techniques 2) Stable Internal Fixation: Locking screws increase stability in osteoporotic and metaphyseal bone DJ 4213

Locking Plates & Screws 3) Preservation of Blood Supply: Limited contact stabilizes fracture without plate-to-bone compression Tapered tip allows submuscular (percutaneous) plate insertion, decreasing tissue destruction DJ 4213

Locking Plates & Screws 4) Early Active Pain Free Mobilization: A more stable construct = earlier return to ADL (Activities of Daily Living) DJ 4213

Summary Now you should be able to: Describe how locking plates are designed and function differently than conventional plates Identify the advantages of locking plates for certain fractures Know the indications for using locking plates: Poor quality bone Metaphyseal fractures Periprosthetic fractures Failed fixation (nonunion) Screw strippage DJ 4213

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