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Structural Allograft

 - structural bone grafts for hip arthroplasty:
        - structural bone grafts and cemented prosthesis may be indicated when there is less than 50% of acetabular contact; 
        - as pointed out by Hasegawa et al 1996, when there was more than 67% of acetabular coverage in dysplastic hips, there were no revisions at 13 years;
        - it has been recommended that w/ 60% to 70% coverage, structural bone grafts are not necessary;
        - if structural bone grafts support more than 50 per cent of the cup, then is should be protected with a reconstruction ring;
        - operative technique for superior structural bone grafting:
               - frozen allograft preparation;
               - acetabular floor is cleared of scar and soft tissue;
               - frozen allograft is thawed and shaped to fit the acetabular defect; (distal femur is often allograft of choice);
               - frozen allograft is thawed, cultures are taken, and graft is placed in 50% Betadine (povidone-iodine) solution; 
               - allograft is rinsed with a mixture of one-third 3% hydrogen peroxide and two-thirds saline solution and then is rinsed with bacitracin; 
        - minor column graft: (see Regenerex)
               - by definition minor column allograft (shelf graft) will support less than 50% of the cup;
               - size and shape of the graft are determined with a trial cup in place;
               - cut surface of allograft is not placed in contact with host soft tissue in order to minimize resorption.
               - graft is fixed with two 4.5-mm cancellous-bone screws;
               - cup can be inserted either with or without cement; 
        - major column graft: (by definition supports greater than 50% of cup surface);
               - graft is shaped to fit the acetabular defect; (distal femur is often allograft of choice); 
               - femoral head grafts should either be from males or premenopausal female donors;
        - distal femoral bulk graft:
               - distal aspect of a femur is sculpted to duplicate an acetabulum;
               - distal femoral allograft with the attached metaphysis was cut into the shape of the number 7;
               - condyles are reamed to accept an acetabular cup;
               - anterior femoral groove and a portion of the metaphysis were positioned outside of the acetabulum, and positioned against the ilium;
               - metaphysis side provides bone for internal fixation to the ilium;
               - remainder of the femoral condyle is placed inside the acetabulum to buttress the ilium; 
               - after screw fixation, reaming is carried out in the usual manner until anterior and posterior columns are encountered; 
               - bulk allograft should be butressed within the host acetabular defect rather than applied on the lateral wall of the ilium;
               - align the graft trabeculae along the wt bearing axis;
               - attempt to butress the graft with the posterolateral portion of the acetabulum;
               - cancellous surface of graft is not positioned against host soft tissue because this allows more rapid resorption than subchondral bone surface;
               - cancellous surface should face the cup;
               - drill small holes in the ilium where it abuts the shelf graft inorder to encourage union and remodeling;
               - contouring is carried out inorder to maximize contact between host and allograft surfaces; 
               - refs: The Use of Structural Distal Femoral Allografts for Acetabular Reconstruction. Average Ten-Year Follow-Up. Cementless Total Hip Arthroplasty with Autologous Bone Grafting for Hip Dysplasia

        - fixation:
               - if pelvic discontinuity exists, then posterior column plating is performed prior to fixation;
               - depending on the size of the graft use at least two 4.5 or 6.5 cancellous lag screws placed over washers;
               - screws need to be placed parallel to each other and along the wt bearing forces;
               - screw threads should be in the host bone and not in the graft;
               - screw placement should not interfere with component placement;
               - use of a acetabular reconstruction ring and cement may be key elements of long term success found in some series;
               - if more than 50% of the socket is involved, the cup will have to be cemented; 
        - reaming: 
               - following application of the graft, reaming is performed in the usual manner; 
        - results of structural grafting:
               - historically, non-contained defects of the acetabular column which involve more than 50% of the acetabulum have had mixed results;
               - when graft coverage is less than 30%, results are markedly improved;
               - many are pesimistic about the fate of massive allografts applied to the acetabulum w/o cement;
               - main mode of failure of bone grafts (esp allografts) occurs as a result of collapse and graft resorption; 
        - complications of bulk grafts:
               - clinical failure:
               - structural acetabular allografts may fail in 50% of cases at 10 years;
               - failure of autogenous graft to unite w/ host bone;
               - success of graft fixation is directly related to amount of contact area;
               - w/ autogenous femoral head grafts, success of graft fixation appears to diminish significantly when contact area is less than 50%;
               - at 16 years, less than 20% of these grafts will be rigidly fixed;
               - in contrast, when contact area is more than 70% there is a high success rate of graft fixation;
               - hence, the hip revisions that require bulk grafts for fixation (ie lack of contact), will be at the highest risk of graft failure;
               - resorption of the graft (determined by comparing recent radiographs with radiographs taken immediately postop);

Management of massive acetabular defects in revision total hip arthroplasty.
Revision of the Acetabular Component of a Total Hip Arthroplasty with a Massive Structural Allograft. Study with a Minimum Five-Year Follow-Up.
Use of structural allografts in acetabular revision surgery.
Principles of bone grafting in revision total hip arthroplasty: Acetabular technique.
The fate of acetabular allografts after bipolar revision arthroplasty of the hip. A radiographic review. 
Telescopic Mating Technique for Bulk Allograft Reconstruction