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Implant screw plate

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Implant screw plate

  1. 1. PLATES AND SCREWS: An Overview Presented by : Dr. REM KUMAR RAI
  3. 3. SCREW: INTRODUCTION  An elementary machine to change the small applied rotational force into a large compression force  Function  Holds the plate or other prosthesis to the bone  Fixes the # fragments ( Position screw)  Achieves compression between the # fragments (Lag screw)
  4. 4. Screw: Parts  4 functional parts  Head  Shaft  Thread  Tip shank
  5. 5. Head: Function  1. Means for applying torque with a screwdriver  2. Acts as a stop (the undersurface) i.e. countersunk
  6. 6. Head: Recess Types  1. Slotted  2. Cruciate  3. Philips  4. Hex/ Allen  5.Torx (eg Stardrive of Synthes)
  7. 7. Head: Countersink  Undersurface of head  Conical  Hemispherical  Morse-cone (steep): locking plates
  8. 8. Screw: Shaft/ Shank  Smooth link  Almost not present in standard cortex screw  Present in cortical SHAFT SCREW or cancellous screw
  9. 9. Screw: Run out  Transition between shaft and thread  Site of most stress riser  Screw break  Incorrectly centered hole  Hole not perpendicular to the plate
  10. 10. Screw: Thread  Inclined plane encircling the root  Single thread  May have two or more sets of threads  V-thread profile: more stress at sharp corner  Buttress thread profile: less stress at the rounded corner
  11. 11. Screw: Core Diameter  Narrowest diameter across the base of threads  Also the weakest part  Smaller root  shear off  Torsional strength varies with the cube of its root diameter
  12. 12. Screw: Pitch and Lead  Distance between the adjacent threads  Cortex screw : small pitch 1.75mm  Cancellous screw: large pitch  Pitch also determines the lead  Lead :distance advanced in a complete turn  Equals pitch in single threaded screw  Greater M.A. if smaller lead
  13. 13. Screw: Thread Diameter  Diameter across the maximum thread width  Affects the pull out strength  Cancellous have larger thread diameter
  14. 14. Screw: Tip Designs  1. Self-tapping tip:  Flute  Cuts threads in the bone over which screw advances  Cutting flutes chisel into the bone and direct the cut chips away from the root
  15. 15. Screw: 2.Non self tapping  Lacks flutes  Rounded tip  Must be pre-cut in the pilot hole by tap  Pre-tapped threads help to achieve greater effective torque and thus higher inter- fragmental compression  Better purchase
  16. 16. Screw: 3.Corkscrew tip  Thread forming tips  In Cancellous screws which form own threads by compressing the thin walled trabecular bone  Inadequate for cortical bone
  17. 17. Screw: 4.Trochar Tip  Like self tapping  Displaces the bone as it advances  Malleolar screw  Schanz screws  Locking bolts for IMIL
  18. 18. Screw: 5.Self drilling self tapping  Like a drill bit  In locked internal fixator plate hole  Pre-drilling not required  Good purchase in osteoporotic and metaphyseal area
  19. 19. Locking Screws vs Cortical 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
  20. 20.  Bending stiffness proportional to the core diameter  Pull out strength is proportional to the size of the thread  Cannulated screws have less bending stiffness
  21. 21. Machine and Wood Screws  Wood  Used in wood  Large threads , usually tapered  Pilot hole is small  Elastic force from deformation of wood  Machine  Used in metals  Pilot hole matches the size of the screw core  Tapped  Elastic force from deformation of the screw itself
  22. 22.  Tensile strength is directly proportional to the squared core diameter d2  Pull out strength is depends on the outer diameter  Shear strength is directly proportional to the cubed core diameter d3.
  23. 23. AO/ASIF Screws: Types  Cortical  Fully threaded  Shaft screw  1.5:phalanx *drill bit 1.1 mm  2.7: mc and phalanx *bit:2.0  3.5: Radius/ Ulna/ Fibula/ Clavicle*bit:2.5  4.5: Humerus/Tibia/ femur *bit:3.2  2:phalanx
  24. 24.  Cancellous  Fully threaded  Cannulated or Non- cannulated  Partially threaded  16mm or 32 mm  Cannulated or Non-cannulated  4.0, drill bit 2.5mm humeral condyle  6.5 drill bit 3.2mm tibial and femoral condyle
  25. 25.  Cannulated screws  3.0  4.0  4.5  6.5  7.0  7.3
  26. 26.  Locking screws synthes  2.4mm  3.5mm  4.0mm  5.0mm  7.3mm
  27. 27. AO/ASIF Screws • Cancellous screws: – a wood type – core diameter is less – the large threads – Higher pitch – Greater surface are for purchase – Untaped pilot hole – Pilot hole equals the core diameter – lag effect option with partially threaded screws – theoretically allows better fixation in soft cancellous bone.
  28. 28. AO/ASIF Screws • Cortical screws: – a machine type – Smaller threads – Lower pitch – Large core diameter – Smaller pitch higher holding power – greater surface area of exposed thread for any given length – better hold in cortical bone
  29. 29. Special Screws  Herbert Screw  Dynamic Hip Screw  Malleolar Screw  Locking bolt  Interference screw  Suture anchor  Acutrak screw  Pedicle screw
  30. 30. Herbert Screw  Specialized to achieve interfragmentary compression  Headless  Threads at both ends  Pitch differential between the leading and trailing threads  Compression by the difference in thread pitch  Coarser pitch moves a greater distance with each turn than does the finer pitch
  31. 31. Clinical application:Lag Screw  Used to compress fracture fragments  Use to hold plates on bone  Threads only engage far cortex  Can be achieve with: - Partially threaded screw - Fully threaded with over drilling near cortex
  32. 32. Clinical Application: Positional Screw
  33. 33. Lag Screw PartiallyThreaded cancellous screw Threads must be completely across the fracture to achieve compression and purchase far cortex if possible
  34. 34. PLATES Introduction :  Bone plates are like internal splints holding together the fractured ends of a bone.
  35. 35. Mechanical functions of plate 1. Transmit forces from one end to another, bypassing and thus protecting the area of fractures. 2. Holds the fracture ends together in alignment throughout the healing process.
  36. 36. Names of plates. 1. Shape (Semitubular, 1/3rd tubular) 2. Width of plate (Small, Narrow, Broad) 3. Shape of screw holes. (Round, Oval) 4. Surface contact characteristics. (LC, PC) 5. Intended site of application (Condylar Plate) 6. According to the function
  37. 37. Type of plate – Functional  Regardless of their length, thickness, geometry, configuration and types of hole, all plates may be classified in to 4 groups according to their function. 1. Neutralization plate. 2. Compression plates. 3. Buttress plate. 4. Tension band plates.
  38. 38. Standard Plates  Narrow DCP-4.5 mm  Broad DCP – 4.5 mm,3.5 mm DCP  LC-DCP 3.5 & 4.5mm  Reconstruction plate 3.5 & 4.5mm  1/3 tubular plate 2.7, 3.5 & 4.5 mm
  39. 39. Special Plates  T Plates  T&L Buttress plates  LateralTibial head buttress plates  Condylar buttress plate  Narrow lenthening plates  Broad Lengthening plate  Spoon plate  Clover leaf plate
  40. 40. NEUTRALIZATION PLATE • Acts as a ""bridge”” protection • No compression at the fracture site • neutralization plate is to protect the screw fixation of • a short oblique fracture • a butterfly fragment • a mildly comminuted fracture of a long bone • fixation of a segmental bone defect in combination with bone grafting.
  41. 41. The Neutralization Plate  Lag screws:  compression and initial stability  Plate:  protects the screws from bending and torsional loads
  43. 43. COMPRESSION PLATE • produces a locking force across a fracture site • Newton's Third Law (action and reaction are equal opposite) • plate is attached to a bone fragment then pulled across the fracture site by a device, producing tension in the plate • direction of the compression force is parallel to the plate
  44. 44. COMPRESSION Static: does not change with time Dynamic: periodic partial loading & unloading due to functional activity 1. Tension Band wiring 2. Tension Band Plating
  45. 45. BONE UNDER COMPRESSION • Superior stability – Utilization of physiological forces • Improved milieu for bone healing • Early mobilization
  46. 46. DCP (Dynamic Compression Plate): Principle : - a self compression plate due to the special geometry of screw holes which allow the axial compression.
  47. 47. Dynamic compression principle: screw head slides down the inclined plate hole as it is tightened, with the head forcing the bone-screw to move towards the fracture, thereby compressing the fracture
  48. 48. • Screw hole and the spherical gliding principle. • Axial compression result from the an interplay between screw hole geometry and eccentric placement of the screw in the screw hole.
  49. 49. The shape of the holes of the dynamic compression plate allows inclination of the screws in a transverse direction of +7° and in a longitudinal direction of 25°.
  50. 50. Advantage of DCP : 1. Inclined insertion 25°longitudinal and 7° sideways 2. Placement of a screw in neutral position without the danger of distraction of fragments 3. Insertion of a lag screw for the compression 4. Usage of two lag screws in the main fragments for axial compression 5. Compression of several fragments individually in comminuted fractures 6. Application as a buttress plate in articular area
  51. 51. Shortcomings of DCP : 1. Flat under surface. 2. Inclination upto 25° 3. Plate hole distribution (extended middle segment)
  52. 52. The structure of a limited- contact dynamic compression plate 1.Structured undersurface 2.Undercut screw holes 3.Trapezoid cross section LC-DCP
  53. 53. In the DCP (A), the area at the plate holes is less stiff than the area between them so while bending, the plate tends to bend only in the areas of the hole. The LC-DCP(B) has an even stiffness without the risk of buckling at the screw holes.
  54. 54.  The LC-DCP offers additional advantage  Improve blood circulation by minimizing plate- bone contact  More evenly distribution of stiffness through the plate  Allows small bone bridge beneath the plate
  55. 55.  The trapezoid cross section of the plate results in a smaller contact area between plate and bone.  The plate holes are uniformaly spaced, which permits easy positioning of the plate.  Undercuts plate holes; undercut at each end of the plate hole allows 40 tilting of screws both ways along the long axis of the plate. Lag screw fixation of short oblique fractures is thereby possible.
  56. 56. Sizes of DCP Name of plate Small Narrow Broad Width 11 mm 13.5 mm 17.5mm Profile 4 mm 5.4 mm 5.4 mm Screw 2.7 , 3.5 cortex screw and 4 mm cancellous screw 4.5 mm cortex screw & 6.5mm canellous screw 4.5 mm cortex screw & 6.5mm canellous screw Sizes of LCDCP Name of plate Small Narrow Broad Width 11 mm 13.5 mm 17.5mm Profile 4 mm 5.4 mm 5.4 mm Screw 2.7 , 3.5 and 4 mm cancellous screw 4.5 mm & 6.5mm canellous screw 4.5 mm & 6.5mm canellous screw Name of plate Small Narrow Broad Width 11 mm 13.5 mm 17.5mm Profile 4 mm 5.0 mm 5.0 mm Screw 4 mm locking screw 5 mm locking screw 5 mm locking screw Sizes of LCP
  57. 57. BUTTRESS PLATE • is to strengthen (buttress) a weakened area of cortex • The plate prevents the bone from collapsing during the healing process. • A buttress plate applied a force to the bone which is perpendicular (normal) to the flat surface of the plate.
  58. 58. • The fixation to the bone should begin in the middle of the plate, i.e. closest to the fracture site on the shaft. The screws should then be applied in an orderly fashion, one after the other, towards both ends of the plate. BUTTRESS PLATE
  59. 59. Bridge Plating : Bridge Plating for comminuted fracture -instead of individually fixing each fragment -minimal disruption to blood supply -reduction is performed indirectly - compression is only sometimes possible
  60. 60. Wave Plating : Wave Plating for non union
  61. 61. ADDITIONAL PRINCIPLES OF PLATE FIXATION  The engineering principle of the tension band is widely used in fracture fixation. It applies to the conversion of tensile forces to compression forces on the convex side of an eccentrically loaded bone.
  62. 62. Reconstruction Plates :  Can be bent and twisted in two dimensions.  Decrease stiffness than DCP.  Should not be bent more than 15°.  Used were the exact and complex contouring is required. eg. Pelvis, Distal Humerus, Clavicle.
  63. 63. Reconstruction plates are thicker than third tubular plates but not quite as thick as dynamic compression plates. Designed with deep notches between the holes, they can be contoured in 3 planes to fit complex surfaces, as around the pelvis and acetabulum. Reconstruction plates are provided in straight and slightly thicker and stiffer precurved lengths. As with tubular plates, they have oval screw holes, allowing potential for limited compression.
  64. 64. One Third Tubular Plates :  Plates have the form of one third of the circumference of a cylinder.  Low rigidity (1mm thick).  Oval holes – Axial compression can be achieved.  Uses – Lateral malleolus, distal ulna, metatarsals.
  65. 65. limited stability. The thin design allows for easy shaping and is primarily used on the lateral malleolus and distal ulna. The oval holes allow for limited fracture compression with eccentric screw placement.
  66. 66. LOCKING COMPRESSION PLATE (LCP) Principle :  Angular-stability whereas stability of conventional plates is friction between the plate and bone  Screw locking principle  Provides the relative stability  Healing by callus formation (Secondary Healing)
  67. 67. LCP: internal external fixator
  68. 68. Stability under load By locking the screws to the plate, the axial force is transmitted over the length of the plate secondary loss of the intraoperative reduction is reduced Blood supply to the bone No additional compression after locking Periosteal blood supply will be preserved
  69. 69. Unicortical Fixation Conventional Plating SmallSmall LoadLoad SmallSmall LoadLoad Screws have single point of fixation Screws have two points of fixation Locked Plating
  70. 70. Principle of internal fixation using LCP : 1. 1st reduced the # as anatomical as possible 2. Cortical screw should be used 1st in a fracture fragment 3. If the locking screw have been put, use of the cortical screw in the same fragment without loosening and retightening of the locking screw is not recommended 4. If locking screw is used first avoid spinning of plate 5. Unicortical screws causes no loss of stability
  71. 71. 6. Osteoporotic bones bicortical screws should be used. 7. In the comminuted # screw holes close to the fracture should be used to reduce stain. 8. In the fracture with small or no gap the immediate screw holes should be left unfilled to reduced the strain.
  72. 72. Indications : 1. Osteoporotic # 2. Periprosthetic # 3. Multifragmentry # 4. Delayed change from external fixation to internal fixation. Advantages : 1. Angular stability 2. Axial stability 3. Plate contouring not required 4. Less damage to the blood supply of bone 5. Decrease infection because of submuscular technique 6. Less soft tissue damage
  73. 73. HOW MANY SCREWS ?  Hands-on experience suggests that, in the humerus, screws grip seven cortices on each side of the fracture ; in the radius and the ulna, five; in the tibia, six, and in the femur, seven. Bones No. of Cortices No. of Holes Type of Plate Forearm 5 to 6 Cortex 6 holes Small 3.5 Humerus 7 to 8 Cortex 8 holes Narrow 4.5 Tibia 7 to 8 Cortex 7 holes Narrow 4.5 Femur 7 to 8 Cortex 8 holes Narrow 4.5 Clavicle 5 to 6 Cortex 6 holes` Small 3.5
  74. 74. HOW CLOSE TO THE FRACTURE SITE?  A screw, as a result, should not be placed closer than one centimeter from the fracture line.
  75. 75. Timing of Plate Removal, Recommendations for removal of plates in the lower limb :  Bone / Fracture  Time after implantation in months  Malleolar fractures  8-12  The tibial pilon  12-18  The tibial shaft  12-18  The tibial head  12-18
  76. 76.  The femoral condyles  12-24  The femoral shaft: Single plate, Double Plate  24-36  From month 18, in 2 steps ( Interval 06 months)  Pertrochanteric and femoral neck fractures Upper extremity  12-18  Optional  Shaft of radius / ulna  24-28  Distal radius  8-12  Metacarpals  4-6
  77. 77. DIFFERENT AO SCREWS LARGE STANDARD SCREWS. 4.5 mm Cortex Screw 6.5 mm Cancellous Screw Malleolar Screw 4.5 CANNULATED SCREW SYSTEM 6.5 Cannulated Screw 4.0 mm Cannulated Screw 3.5 Cannulated Screw SMALL FRAGMENT SCREW 3.5 mm Cortical Screw 4.0 Canceleous Screw -Partially Threaded. -Fully Threaded MINI SCREW 2.7 mm Cortex Screw 2.0 mm Cortex Screw 1.5 mm Cortex Screw
  78. 78. Screw Core diam eter Threa d diame ter Pitch Drill bit for glidin g hole Drill bit for thread hole Tap diame ter Large Standa rd Screws 7mm Cancello us Screw 4.5m m 7mm 2.75m m 4.5m m 7mm 6.5mm cancello us screw 3.5m m 6.5m m 2.7mm 3.2m m 4.5m m 6.5m m 4.5mm cancello us screw 4.5m m 3.1m m 1.75m m 3.2m m 4.5m m 4.5mm cortical 3mm 4.5 mm 1.75m m 4.5m m 3.2m m 4.5m m
  79. 79. Small Fragme nt Screws 3.5mm cancello us screw 2.5m m 3.5m m 1.25m m 2.7m m 3.5m m 4mm Cancello us screw 1.9m m 4mm 1.75m m 2.5m m 4mm 3.5mm Cortex Screw 2.4m m 3.5m m 1.25m m 3.5m m 2.5m m 3.5m m Mini Fragme nt Screws 2.7mm Cortex Screw 1.9m m 2.7m m 1mm 2.7m m 2mm 2.7m m 2mm Cortex Screw 1.3m m 2mm 0.6mm 2mm 1.5m m 2mm 1.5mm Cortex Screw 1mm 1.5m m 0.5mm 1.5m m 1.1m m 1.5m m