Cementless fixation for primary segmental bone tumor endoprostheses

To combat the high incidence of aseptic loosening for young patients and fo r patients with failed implants after resection for bone tumors, intramedul lary cementless fixation of massive tumor implants was investigated, These implants consist of a hydroxyapatite coated titanium stem. To date, 47 of t hese prostheses have been inserted for the treatment of primary bone tumors . Radiographs indicate that the stems are osseointegrated. Radiolucent line s have not been seen between the implant and the bone. Bone remodeling chan ges have been observed. In several cases in which the implant was not seate d properly on the transaction site, bone grew to the shoulder of the implan t. Bone remodeling was particularly evident in stems that were coated over their entire surface. In these cases, the implant induced local bone resorp tion so that the bone around the midstem region became thinner, with resorp tion of cortical bone on the periosteal surface and maintenance of bone an the endosteal surface adjacent to the stem. This effect was attributed to s tress shielding, and a three-dimensional finite element model using loading data obtained from a telemetry study indicated that, where the stem was bo nded to the bone over the entire surface, stresses in the outer cortex beca me reduced. In the finite element model, reducing the region of hydroxyapat ite coating to approximately 1/3 of the stem length reduced the extent of t he low-stress area in the outer cortex. Subsequently, prostheses have been coated with hydroxyapatite over only approximately 1/3 of their stem, This method of fixing the massive endoprosthesis to the bone is thought to be su ccessful in the short-term and offers an alternative to cemented fixation.