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Twelve knees in ten patients had revision total knee replacement with insertion of an allograft for a large tibial defect. The knees were retrospectively evaluated at an average of thirty-two months (range, twenty-five to fifty-one months) by clinical examination, radiography, planar bone scintigraphy, and single-photon-emission computed tomography. The average age of the patients was sixty-two years (range, fifty-four to seventy-nine years). A constrained total-condylar prosthesis was used for all revisions. A contained tibial defect was present in five knees, and seven knees had an uncontained defect that was treated with a massive composite structural allograft, five of which were secured with internal fixation. The knee scores improved from an average of 51 points before operation to an average of 87 points post-operatively. Seven knees had a score of 85 points or more and were considered to have an excellent clinical result. Two knees had a good result, with scores of 77 and 72 points. One knee had another revision because of painful non-union of a medial structural graft, and the result in that knee was considered a failure. The average range of motion improved from 84 degrees to 105 degrees. There were no deep infections, and no graft showed evidence of fracture or collapse. Radiographs demonstrated complete incorporation of the graft in eleven of the twelve knees at an average of twenty-three months after operation. Single-photon-emission computed-tomography scans showed uniform activity in the area of the graft in four of the five knees that were studied.