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Suzhou Xinrong Best Medical Instrument Co., Ltd.

[Province: Jiangsu ]

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Non - Locking 4 Holes Orthopedic Trauma Implants For HA3.5 / HA4 Screws

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Non - Locking 4 Holes Orthopedic Trauma Implants For HA3.5 / HA4 Screws

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trauma implants Common plates orthopedic implants -in XRBEST 4117

Screws

Definitions
- pitch
  - distance between threads
- lead
  - distance advanced with one revolution
- screw working distance (length)
  - defined as the length of bone traversed by the screw
- outer diameter
- root (inner) diameter
- pullout strength
  - maximized by
    - large inner-outer diameter difference
    - fine pitch
  - pedicle screw pullout most affected by degree of osteoporosis
Types of screws
- cortical screws
- cancellous screws
- locking screws

Plate Properties

Overview & definitions
- a load-bearing device that is most effective when placed on the tension side
- plate working distance
  - the length between the 2 screws closest to the fracture on each end of the fracture.
  - decreasing the working distance increases the stiffness of the fixation construct
Material Properties
- bending rigidity proportional to thickness to the 3rd power
- titanium has Young's modulus of elasticity that most closely approximates cortical bone
Biomechanics
- absolute stability
  - constructs heal with primary (Haversian) healing
  - must eliminate micromotion with lag screw fixation
  - must be low strain at fracture site with high fixation stiffness
- relative stability
  - constructs heal with enchondral healing
  - strain rates must be <10%, or fibrous union will predominate

Plate Variations

Concave plates
- placing a concave bend on a plate is useful in transverse fractures to ensure compressive forces occur on both the far and near cortices of the fracture
Compression plate
- compression plates work by placing a cortical screw eccentrically into an oval hole in the plate
Locking plates
- advantages of locking plates
  - locked plate/screw constructs compared to non-locked plate/screw constructs result in less angulation in comminuted metaphyseal fractures
- indications for locking plate technology
  - indirect fracture reduction
  - diaphyseal/metaphyseal fractures in osteoporotic bone
  - bridging severely comminuted fractures
  - plating of fractures where anatomical constraints prevent plating on the tension side of the bone (e.g. short segment fixation).
- locking plate screw biomechanics
  - bicortical locking screws have significantly more resistance to all applied forces, with resistance to torsion increased the most (versus unicortical)
  - unicortical locking screws have less torsion fixation strength than non-locking bicortical constructs
- percutaneous locking plates
  - application has less soft-tissue stripping but higher chance malunion
- hybrid locked plates
  - utilize locking and nonlocking screws in order to assist with fracture reduction (nonlocking screws) as well as provide a fixed angle construct (locking screws).
- locking plate construct stability increases with:
  - bicortical locking screws
  - increased number of screws
  - screw divergence from screw hole < 5 degrees
  - longer plate
Bridging plates
- provides relative stability, relative length and alignment
- preserves the blood supply to the fracture fragments as the fracture site is undisturbed during the operative procedure
  - this theoretically improves secondary bone healing
- allows some motion at fracture site; relative stability leads to callus formation

Intramedullary nails

Overview
- a load-sharing device
Material Properties
- stiffness
  - torsional rigidity
    - defined as amount of torque needed to produce torsional (rotational) deformation
    - proportional to the radius to the 4th power
    - depends on
      - shear modulus
      - polar moment of inertia
    - increased by reaming
    - decreased by slotting of nail
  - bending rigidity
    - proportional to the radius to the 4th power for a nail
    - depends on
      - material properties
        Young modulus of elasticity of material
      - structural properties
        area moment of inertia
        length
Radius of curvature
- intramedullary nail radius of curvature is greater (straighter) than the radius of curvature of the femur
Interlocking options
- dynamic locking-->axially and rotationally stable fractures
- static locking-->axially and rotationally unstable fractures
- secondary dynamization for nonunion
  - remove proximal interlocking screw or move proximal interlocking screw from the static to dynamic slot

External fixators

Factors that increase stability of conventional external fixators
- contact of ends of fracture
- larger diameter pins (most important)
- additional pins
- decreased bone to rod distance
- pins in different planes
- increasing size or stacking rods
- rods in different planes
- increased spacing between pins
Factors that increase stability of circular (Ilizarov) external fixators
- larger diameter wires
- decreased ring diameter
- olive wires
- extra wires
- wires cross perpendicular to each other
- increased wire tension
- placement of two central rings close to fracture
- increased number of rings

Total Hip Implants

Material Properties
- rigidity depends on length and radius of femoral stem
Biomechanics
- place femoral component in neutral or slight valgus to reduce moment arm and stress on cement
- increasing femoral offset does the following
  - advantages
    - moves abductor moment away from center of rotation
    - increase abductor moment arm
    - reduces abductor force required for normal gait
  - disadvantages
    - increased strain on implant
    - increases strain on medial cement mantle