A Biomechanical Evaluation of Press-Fit Stem Constructs for Tumor Endoprosthetic Reconstruction of the Distal Femur Peter C. Ferguson, MD, FRCSC,*§ Rad Zdero, PhD, y Emil H. Schemitsch, MD, FRCSC, z§ Benjamin M. Deheshi, MD, FRCSC,*§ Robert S. Bell, MD, FRCSC,*§ and Jay S. Wunder, MD, FRCSC*§ Abstract: This study was designed to assess the biomechanical parameters of the older Kotz Modular Femur Tibia Reconstruction (Stryker Inc, Mahwah, NJ) stem and the newer Restoration and the unfluted Global Modular Replacement System (Stryker Inc, Mahwah, NJ) uncemented stems for use with tumor endoprostheses as well as to assess the optimal reaming technique for insertion of these stems. Fresh-frozen adult femora or composite distal femora were implanted with the uncemented stems. Separate experiments were performed to compare reaming technique and bone resection level. All constructs were mechanically tested for axial compression, lateral bending, and torsional stiffness and torque to failure. Results showed that the biomechanical performance of all the stems were similar with respect to each parameter. Cylindrical reaming was associated with a significantly higher torque to failure than flexible reaming in the diaphysis (P = .006). Newer uncemented stems provide adequate initial biomechanical stability for implantation in the distal femur. Keywords: tumor endoprosthesis, uncemented stem, biomechanical analysis, loosening, Femur. © 2011 Elsevier Inc. All rights reserved. Advances in chemotherapy over the past 30 years have resulted in significant improvements in survival for osteosarcoma [1] and Ewing sarcoma [2], 2 of the more common primary bone cancers. As a result of this improved survival, endoprosthetic replacement has become the standard reconstruction technique in most musculoskeletal oncology centers after resection of lower extremity bone sarcomas. This technique provides functional outcomes that are clearly superior to the more traditional extremity amputation, which was used widely before the advent of modern chemotherapy. The current expectation is that patients undergoing endo- prosthetic replacement for bone sarcomas will have a relatively normal lifespan and therefore will need extended prosthetic longevity. There continue to be proponents of both cemented and cementless fixation of tumor endoprostheses. Although cemented fixation has the advantage of immediate stability, most early long-term studies of cemented endoprostheses, particularly when used around the knee, show a high rate of aseptic loosening [3-6]. This may result in the necessity for repeated revisions, thereby minimizing the longevity of the prosthesis. This phenomenon may be of historic relevance only, however, as a more recent study by Schwartz et al [7] has suggested that the aseptic loosening rate of cemented prostheses may be improving. Most studies of cementless tumor endo- prostheses have demonstrated a very low aseptic loosening rate [8-13]. A well-ingrown cementless stem is likely to provide the patient with a durable and reliable long-term reconstruction. The Kotz Modular Femur Tibia Reconstruction system (KMFTR; Stryker Inc, Mahwah, NJ) has been a widely used uncemented tumor prosthesis system. We previ- ously demonstrated an extremely low rate of aseptic loosening with this system [8]. One proposed reason for the low aseptic loosening rate in this study is that the stem was inserted after flexible reaming rather than rigid From the *University Musculoskeletal Oncology Unit, Division of Orthopaedic Surgery, Mount Sinai Hospital, Toronto, ON, Canada; yMartin Orthopaedic Biomechanics Lab, St Michael's Hospital, Toronto, ON, Canada; zDivision of Orthopaedic Surgery, St Michael's Hospital, Toronto, ON, Canada; and §Division of Orthopaedic Surgery, Department of Surgery, University of Toronto, Toronto, ON, Canada. Submitted January 22, 2010; accepted December 5, 2010. The Conflict of Interest statement associated with this article can be found at doi:10.1016/j.arth.2010.12.005. Reprint requests: Peter C. Ferguson, MD, FRCSC, Mount Sinai Hospital, 600 University Ave., Suite 476G, Toronto, ON, Canada, M5G 1X5. © 2011 Elsevier Inc. All rights reserved. 0883-5403/2608-0040$36.00/0 doi:10.1016/j.arth.2010.12.005 1373 The Journal of Arthroplasty Vol. 26 No. 8 2011