- 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