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Long-Term Results of Segmental Prosthesis Fixation by Extracortical Bone-Bridging and Ingrowth
Edmund Y.S. Chao, PhD1; Bruno Fuchs, MD1; Charles M. Rowland, MS1; Duane M. Ilstrup, MS1; Douglas J. Pritchard, MD1; Franklin H. Sim, MD1
1 Departments of Orthopedic Surgery (E.Y.S.C., B.F., D.J.P., and F.H.S.) and Health Sciences Research (C.M.R. and D.M.I.), Mayo Clinic, 200 First Street S.W., Rochester, MN 55905. E-mail address for F.H. Sim: sim.franklin@mayo.edu
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In support of their research or preparation of this manuscript, one or more of the authors received a grant from the National Institutes of Health (NIH-NIC Grant CA 23751). None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at the Departments of Orthopedic Surgery and Health Sciences Research, Mayo Clinic, Rochester, Minnesota

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2004 May 01;86(5):948-955
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Background: The technique of extracortical bone-bridging and ingrowth fixation with a porous coating over the shoulder region of the implant and augmentation by autogenous bone-grafting was introduced to improve the longevity of implant fixation. The potential advantages of this technique are that new-bone formation across the bone-prosthesis junction may share stress and may prevent osteolysis by sealing off this critical region against the infiltration of wear particles. The objectives of this study were to examine the prevalence of stem-loosening with use of the extracortical bone-bridging and ingrowth technique, the amount of bone formation over the porous-coated region of this prosthesis, and the characteristics of bone formation over the porous-coated region and adjacent bone.

Methods: Forty-three patients who had prosthetic reconstruction with the extracortical bone-bridging and ingrowth technique from 1976 to 1990 were included in this retrospective study. The mean length of follow-up was 9.7 years (range, two to twenty-one years). All but one patient were managed with autogenous bone graft; five, with allograft and autograft; and one, with allograft only. Extracortical bone formation was measured over a 2-cm length of the porous-coated region of the prosthesis in four zones (the medial and lateral aspects on anteroposterior radiographs and the anterior and posterior aspects on lateral radiographs) and was reported as the percentage of the total length (8 cm) covered by extracortical bone with a thickness of >1 mm. The Spearman rank coefficient was used to assess the correlation between pairs of continuous variables.

Results: The final average percentage of the porous-coated region that was covered by extracortical bone formation was 76% ± 34% for all patients and anatomical sites of reconstruction. Use of bone cement was associated with less bone formation (p = 0.04), and this value remained lower at the final measurement (p = 0.06). One stem had aseptic loosening, but no sign of osteolysis was found. The radiographic appearance of the bone formation had stabilized at two years of follow-up. All patients with allograft augmentation had greater bone formation. The amount of extracortical bone formation did not differ in relation to the type of porous coating, anatomical sites, pathological disorder, sex or age of the patient, or length of reconstruction.

Conclusions: As shown by the low prevalence of stem-loosening (two of fifty-six stems or one of forty-three patients), the use of the extracortical bone-bridging and ingrowth fixation technique is associated with improved stem fixation in segmental bone-replacement prostheses applied for limb salvage. In the demanding biomechanical environment and with the risk of stress and particle-related bone resorption, the extracortical bone-bridging and ingrowth fixation is an attractive method to provide long-lasting implant fixation.

Level of Evidence: Therapeutic study, Level IV (case series [no, or historical, control group]). See Instructions to Authors for a complete description of levels of evidence.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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