Impaction Bone Grafting for Defects in Revision Total Knee Arthroplasty

P ITFALLS

• Use of wire mesh for uncontained femoral defects is difficult and time consuming, and other reconstructive options may be more suitable.

 

Impaction Bone Grafting for Defects

 

Indications

• Contained femoral metaphyseal and epiphyseal defects

• Contained proximal tibial metaphyseal and epiphyseal defects

• Uncontained proximal tibial and distal femoral defects, in combination with wire mesh

  Controversies

  • Alternative methods of biologic restoration using bulk allograft may be considered. Metallic augments and metaphyseal cones allow immediate weight bearing, providing immediate strength and eliminating the need for biologic incorporation.

   

  Examination/Imaging

• Standing anteroposterior, lateral, and sunrise radiographs should be used to evaluate all painful total knee arthroplasties.

  • In Figure 1, anteroposterior (Fig. 1A) and lateral (Fig. 1B) radiographs show a failed revision total knee arthroplasty with subsidence of the tibial component, polyethylene wear, and osteolysis beneath the tibial tray and posterior femur.

    Treatment Options

    • Alternative treatment options include:

      • Cement

      • Reinforced cement

      • Metallic augments

      • Metaphyseal porous metal cones

      • Structural allograft

     

  • It is well recognized that standard radiographs routinely underestimate the extent of osteolysis.

• Special-sequence magnetic resonance imaging or computed tomography scans may be useful imaging studies to further delineate preoperatively the extent of periarticular bone loss.

   

   

   

  A B

  FIGURE 1

   

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  Impaction Bone Grafting for Defects

   

  Surgical Anatomy

  • If wire mesh is to be utilized to buttress uncontained defects of the proximal medial tibia, subperiosteal release of the superficial medial collateral ligament and medial soft tissue sleeve is performed and wire mesh is anchored into the proximal tibia with unicortical screws.

  • For uncontained defects of the posterior femoral condyles, the posterior capsule and gastrocnemius tendons are stripped off the posterior femur.

    Positioning

  • The patient is positioned on the operating table in the standard supine position.

  • The limb is prepped and draped according to the preference of the surgeon.

  • Leg positioners may be utilized to help stabilize the knee in varying degrees of flexion.

    Exposure

  • In general, given the complexity of many revision total knee arthroplasties in the presence of massive bone loss, an extensile medial parapatellar arthrotomy is utilized.

  • Proximal releases such as a quadriceps snip or a tibial tubercle osteotomy can be utilized depending on the quality of bone and location of the defect. A lateral retinacular release may be necessary during the surgical approach to help gain exposure and mobilize the patella.

  • Protecting the patellar tendon attachment on the tibial tubercle is of utmost importance, particularly if there is massive osteolysis in the proximal tibia that compromises the cortical integrity of the anterior tibia.

    Procedure

    Step 1: Allograft Material

  • Fresh frozen cancellous allograft chips should be ordered in advance.

  • Morsels should preferentially be between 0.5 and

  1.0 cm to maintain their integrity long enough to act as an osteoconductive substrate for new bone formation.

  • Morsels less than 0.5 cm tend to be resorbed quickly.

   

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  P EARLS

  • Customized cannulated broaches can be useful for impacting bone graft into the metaphyseal regions. Tapered stems can be customized and utilized for these purposes as well.

     

  • It is unclear whether stems are best cemented or left cementless. If cementless stems are utilized, they should be diaphyseal engaging. For the most part, for large areas of cancellous impaction allografting, it is preferred to utilize cemented stems.

     

  • Defects may typically range in size requiring between 30 cc’s to 150 cc’s of allograft per each hemicondyle.

   

  Impaction Bone Grafting for Defects

   

  • Morsels greater than 1 cm in diameter tend to act like bulk allograft inasmuch as they incorporate slowly and collapse during revascularization.

    • The fresh frozen morselized cancellous graft is first thawed before impacting it into the defect.

    • Avoid crushing morsels during impaction.

      Step 2: Contained Defects

    • After exposure is obtained, complete and thorough synovectomy should be performed.

    • Components are carefully removed.

    • The areas of osteolysis are cleared of adherent fibrous tissue from the underlying endosteal or cancellous bone surfaces.

    • Rongeurs and curettes can be used for the initial stage.

    • Next, 6-mm burrs can be used to decorticate the endostium to expose bleeding surfaces, which will enhance eventual bony ingrowth.

    • Once the zone of defect is established, fresh frozen cancellous morsels are gently impacted into place.

  • To avoid collapse of the morselized bone into the tibial or femoral canals, reaming of the canals can be performed prior to impaction grafting. The reamer or trial stem can be left in place while the bone graft is impacted (Fig. 2). The morsels are loosely tamped into place around the provisional stem.

  • Particularly on the femoral side, the impacted morsels may disassociate from the impacted surfaces and fall into the canals (Fig. 3). A thin coating of polymethylmethacrylate can be applied to the exposed surfaces of cancellous allograft to keep it in place. Alternatively, the allograft can be supported with wire mesh after subperiosteal release of the posterior capsule.

• Once an adequate platform is achieved, trialing and ultimately final implantation can be performed.

  Step 3: Uncontained Defects

• Figure 4 shows an uncontained defect of the medial tibial plateau and deficiency of the posterior femoral condyles.

• Uncontained defects of the proximal medial tibia can be treated with wire mesh attached to the intact cortices with unicortical screws. The alternative is

to rely on the soft tissue sleeve as the source of containment.

 

 

 

 

 

Impaction Bone Grafting for Defects

 

 

 

 

 

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FIGURE 2

 

FIGURE 3

 

FIGURE 4

 

 

 

 

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FIGURE 5

 

Impaction Bone Grafting for Defects

 

• If wire mesh is utilized, a sheet of mesh can be cut to the appropriate size.

• In Figure 5, wire mesh is precut and anchored to the medial tibial metaphysis with unicortical screws.

• Care should be taken to avoid abutment of the wire mesh on the tibial tray. There should be separation by either morselized bone or cement.

• Morsels are impacted into place with the wire mesh buttressing the graft medially (Fig. 6).

• Cement is pressurized into the prepared morselized bed, and components are impacted into place (Fig. 7). Accurate component rotation and axial alignment is absolutely imperative and cannot be compromised.

   

   

   

  FIGURE 6

   

  Complications

  • As in all revision knee replacements, complications can occur, but these have been reported with limited frequency. They include infection, periprosthetic fracture, aseptic loosening, collapse of the bone graft, failure of incorporation, and junctional nonunion.

   

   

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  Impaction Bone Grafting for Defects

   

  FIGURE 7

   

   

   

  Postoperative Care and Expected Outcomes

  • A period of protected weight bearing may be necessary, although the constructs, particularly with cement-bearing stems, have reasonable strength and should be able to accommodate immediate weight bearing. Range of motion is allowed in the typical fashion of revision total knee arthroplasty.

  • Figure 8 shows the outcome after total knee replacement with impaction grafting. Wire mesh had been used for containment on both the medial tibia and posterior femur.