Download as PDF, PPTX
Uploaded byZahid Askar
Biomechanics of locking plates
Locking plates work by converting axial loads into compressive stresses at the screw-bone interface. This increases fixation strength and prevents hardware failure, especially in osteoporotic bone. Locking plates provide stability for early motion while protecting blood supply, aiding fracture healing. Key advantages over conventional plates are increased axial and angular stability with less dependence on bone quality. Proper technique requires initial fracture reduction before plate fixation with a combination of locking and conventional screws. Over-rigid constructs with too many screws can impair healing and cause nonunion.
More Related Content
Similar to Biomechanics of locking plates
Biomechanics of locking plates
- 2. Biomechanics of Locking Plates ZahidAskar FCPS(Ortho), FRCS (Tr & Ortho) Prof & Chair Deptt of Orthopaedics & Trauma Khyber Medical College, Peshawer
- 3. Pre-requisites for agood fixation system • Minimal operative dissection • Minimal periosteal contact • Resist physiological loads to allow fracture union • Provide sufficient stability to permit early limb motion,
- 4. The forces thatmust be overcome by any method of fracture fixation. AXIAL BENDING TORSIONAL
- 5. Axial force iscountered in DCP by A x B B A = (the normal force provided by screw torque) B = (the coefficient of friction between the plate and bone)In osteoporosis or comminuted fractures, the A xB < axial load which would could lead to hardware failure
- 6. Limitations of ConventionalPlates • Failure in Osteopenic Bone------ Geriatrics • Periosteal Avascularity --- ------- Tissue necrosis underneath the plate • Percutaneous Plate ??? In the majority of fractures, conventional plating will do well
- 7.
- 8. Basic Principles ofLocking Plate •Bone compression
- 9. WORK AS AUNIT !!!!
- 10.
- 12.
- 13. Locking Screws vsCortical Screws Creates Fixed Angle Generates Friction/Compression 4.4mm Core Dia. 3.5mm Core Dia. 5.0 mm Locking Screw 4.5 mm Cortical Screw
- 14. Mechanics/biomechanics of plate/screwfixation Plate fixation with conventional screws Plate fixation with locking head screws
- 15. • A lockedplate converts an axial load shear force into a compressive stress at the screw bone interface • The strength of fixation is equal to the sum of the entire screw bone interface of all the screws as opposed to a single screw as in unlocked screws
- 16. Techniqual Advantage • Axialand angular stability • Not preloaded • Cannot be over-tightened • Higher resistance against bending loads • Monocortical insertion is possible • No primary loss of reduction • No or less screw loosening, no or less secondary loss of reduction
- 17. Biological Advantages • Reducedcompression of the periosteum • Protects blood supply to the bone • Callus formation/bone healing under the plate bone after plating with a DCP bone after plating with a LCP
- 18. Type of lockingplates
- 19. Types of LockingScrews • Fixed Angle Locking Plate • Variable Angle
- 23. Indications for Locking •Biological Fixation • Spanning Comminution (bridging) • Percutaneous Techniques • Metaphyseal / Bicondylar Articular Fractures • Short Articular Segment • Periprosthetic Fractures • Osteoporosis
- 24. Short Segment FixationIn Osteoporotic Bone
- 25. Short Segment Fixationwith Conventional Fixation
- 26. Number of Screws •More locking screws will make the fixation very rigid • YOU DO NOT NEED TO FILL ALL HOLES • Conventional and locking screws can be combined 1:2
- 27.
- 28. Stiffness of theconstruct
- 29. Two many screwsdecreases strain Non-union
- 30. To decrease thestiffness and increase the flexibility …….. • Far Cortex Locking screws
- 33.
- 34. Order of Attack 1.Reduce the fracture first 2. For reduction, if you need put to conventional screws - they should be put before the Locking Screws 3. Then fix it with Locking Screws. 4. For Articular Fractures, the articular portion of the fracture is reduced first . 5. Reduce the shaft to the articular block
- 36. Lag screws canbe used to help reduce fragments and construct stability improved w/ locking screws
- 37.
- 38.
- 39.
- 40.
- 41.
- 42.
- 43.
- 44.
- 45. • Too manyscrews • Wrong bone • Wrong fracture
- 46. Problems ---- toomany screws
- 48.
- 49. Problems • Plate bending; •Plate fracture; • Plate pull-off; and • Locking screw failure • Difficult to remove • NON-UNION
- 50. Summary • Locking isa principle • Mostly for Osteoporotic bones • Beware of too rigid fixations • Need Reduction • Good for multifragmentary fracture and MIPO • Biomechanics should be understood