Bone Deficiency in Primary Total Knee Arthroplasty - PowerPoint PPT Presentation

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Bone Deficiency in Primary Total Knee Arthroplasty

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Introduction numerous etiologies exist for presence of bone defects at time of TKA axial ... premature radiolucent lines at augmentation-bone interface ... – PowerPoint PPT presentation

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Title: Bone Deficiency in Primary Total Knee Arthroplasty


1
Bone Deficiency in Primary Total Knee Arthroplasty
  • Douglas Dennis, M.D.
  • Reviewed by K. Ikram, D.O.
  • Jan. 11, 2000

2
Introduction
  • numerous etiologies exist for presence of bone
    defects at time of TKA
  • axial malalignment
  • trauma
  • previous osteotomy
  • prior TKA
  • defects must be localized and classified as
    central or peripheral

3
  • varus deformities charac. assoc. with posteromed.
    defects
  • valgus assoc. with central lateral defect
  • post.lat. defects present following HTO
  • bone defects most frequently occur in prox. tibia

4
  • Goals of reconstruction of bone defects
  • preservation of host bone
  • restoration of anatomic jt. line
  • axial alignment
  • ligamentous stability
  • flex-ext. space symmetry and balance
  • secure implant fixation

5
  • various surgical options available for handling
    such defects including
  • thicker osseous resection
  • shifting the component away from the defect
  • filling the defect with methylmethacrylate (with
    or without screw augmentation)
  • modular prosthetic augmentation

6
  • use of custom-designed components
  • bone graft (auto vs. allograft)
  • purpose of this report is to review the various
    treatment options including indications and
    clinical results of each tx. method.

7
Increased Bone Resection
  • thicker tibial resection to base of defect should
    be reserved for shall defects
  • lt 5 mm medially or lt 10 mm laterally
  • numerous studies show reduction in strength with
    more distal resection
  • lessens osseous support of tibial comp.
  • also may lead use of smaller tibial comp., has
    dec. surface area, leading to inc. unit loading
  • should be limited to pts. of advanced age in
    which revision TKA is unlikely.

8
Component Shifting
  • shifting tibial component medial or lat. away
    from defect may eliminate or reduce the size of
    the defect
  • if shift medially, create a relative
    lateralization of tibial tubercle which may
    result in pat.-fem. instab.
  • a smaller tibial comp. often required again
    diminishing surface area therefore inc. unit load

9
Cement and Screws
  • filling defects with cement alone is simple and
    efficient but premature radiolucent lines often
    develop
  • large mass of cement creates risk of thermal
    necrosis and often difficult to pressurize
  • net shrinkage of 2 as cement polymerizes
  • both math. and biomech. analyses show inf.
    implant support when using this technique
  • Lotke reported success in 58/59 pts at 7 yr f/u
    if bone defect lt 20 mm involved lt 50 of tib.
    condyle

10
  • addition of screws to reinforce strength of
    cement in tx. deficiencies of mod. defects of
    5-10 mm thickness.
  • has same disadv. of cement alone (difficulty of
    pressurization, shrinkage, etc.)
  • Ritter reported on 47 cases and observed no
    prosthetic loosening or failures at 6 yrs f/u.

11
Modular Prosthetic Augmentation
  • early designs were angular in shape and limited
    to tibial component
  • current designs include angular hemi-plateau and
    full plateaus wedges and rectangulat block shapes
    with variable thicknesses
  • also, distal and post. fem. comp. augmentations
    available.
  • repairing defects with these prosthetics allow
    immediate support with satisfactory load transfer

12
  • no risk of disease transmission, malunion,
    nonunion, or resorption.
  • however, size and shape are limited so difficult
    to use with large, irreg. defects.
  • due to modular attachment, potential for debris
    generation and osteolysis is created.

13
  • controversy regarding choice of ang. wedge vs.
    rectangular block augmentations persists
  • angular wedges preserve more host bone
  • rect. augmentations are more biomech. stable
    owing to reduced shear loads at bone-aug.
    interface

14
  • defect bed is often sclerotic and should be
    predrilled to enhance cement pressurization and
    interdigitization into host bone.
  • failure to pre-drill often leads to premature
    radiolucent lines at augmentation-bone interface
  • in cases of large defects, defects with osseous
    fragmenation, or marked obesity, use a diaphyseal
    engaging stem to protect and offload the osseous
    defect and reconstruction.

15
Custom Components
  • similar advantages to the use of modular
    augmentations
  • however, a new modular interface is not created
    so dec. risk of debris-induced osteolysis
  • numerous disadvantages
  • manufacturing delays
  • high costs
  • often poorly fits

16
  • indications limited to pts who have bone defects
    that cannot be managed effectively with modular
    augmentation and are not good candidates for bone
    grafting.

17
Bone Graft
  • offers advantage of bone stock restoration for
    further revisions and ability to contour bone
    graft to fit defect without resection of host
    bone.
  • cost effective, especially if autologous
  • provides more physiologic load transfer if union
    occurs
  • disadvantages include malunion, nonunion, late
    collapse, and disease transmission.

18
  • meticulous surgice technique required for optimum
    results
  • minimum resection of sclerotic bone to create a
    healthy cancellous interface enhance union
  • geometric shaping of host defect and bone graft
    enhance mech. interlock, graft stability, and
    surface contact area available for healing.
  • rigid fixation of bone graft is mandatory to
    assure graft union

19
  • as with prosthetic augmentation, if underlying
    host bed is weakened, addition of
    diaphyseal-engaging stem is warranted to reduce
    loads on graft during incorporation.
  • excellent short term results noted with success
    rates gt 90.

20
Summary
  • numerous options exist for management of minor
    bone defects assoc. with primary TKA
  • biomech. studies show filling defects with cement
    results in inf. load transfer under eccentric
    loading conditions
  • rectangular augmentations may be superior to
    angular wedges owing to reduction in shear
    stresses at fixation interface

21
  • bone graft favored for cavitary defects, massive
    bone loss, and in younger pts in whom additional
    revision surgery is likely
  • prosthetic augmentations favored in peripheral
    defects of moderate size in more elderly pts.
  • preoperative planning is key when dealing with
    any kind of bony defects.

22
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