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Bone defects related to revision knee arthroplasty can be managed with implant supplements, larger implants (mega prostheses), or bone grafts. The factors that determine which method is applicable are related to the size and location of the defect and certain patient characteristics.
BONE DEFECTS
Contained Femoral and Tibial Defects
Defects of the femur and tibia can be managed by morselized bone graft for larger defects in the relatively highdemand patient, or by cement or cement and screws for smaller defects in the low-demand patient.1-3
Uncontained Tibial Defects
Uncontained defects on the tibial side mat are noncircumferential and <2 cm can be managed by implant supplements (full, hemi, or step wedges).1.4 Circumferential tibial defects <45 mm can be treated with a combination of polyethylene (up to 30 mm) and 2 step wedges (15 mm). On the femoral side, implant supplements are limited to circumferential or noncircumferential defects <16 mm.
When bone defects are beyond implant supplements, the surgeon must choose between structural allografts (allograft prosthetic composite) and mega prostheses. Mega prostheses are technically easier, have a faster healing time, are not as adversely affected by chemotherapy or irradiation as allografts, and have no donor or storage problems. Disadvantages include ligament and extensor mechanism reattachment, violation of the host canal by a cemented or porous-coated stem, failure to restore bone stock, and a rotating hinge may be required for stability.5,6 All of these factors make revision difficult. The allograft prosthetic composite offers the advantages of ligament and extensor mechanism reattachment, no violation of host canal by a cemented or porous coated stem, and facilitation of future revisions by restoration of bone stock. Allografts are technically demanding, may transmit disease, and require a longer healing time with the possibilities of nonunion and resorption.7
Mega prostheses are indicated for patients with a guarded prognosis, those at risk for stress fractures, nonunion, and infection (eg, patients undergoing chemotiierapy or irradiation), or patients who would benefit from a shorter and easier rehabilitation. The allograft prosthetic composite is indicated...