The Healing Potential Of Intracorporeally And In Situ Devitalized Distal Femur By Microwave In A Dog Model And Its Mechanical Properties In Vitro

Background and Objective: For the patients with primary malignant bone andsoft tissue tumors, amputation is the only choice before1970s; while even so,the overall survival of10-20%for patients is frustrating. Over the past three orfour decades, the introductions of chemotherapy have increased survivaldramatically to approximately65-75%for patients without clinically evidentmetastatic disease at presentation. Meanwhile, patients are looking forward to abetter functional outcome. Nowadays, limb-salvage surgery has been wellrecognized as a standard treatment and alternative to amputation for thosepatients. In general, limb-salvage surgery involves en bloc resection of bonetumor with a safe margin, followed by reconstruction of the resultant bonedefect. Presently, various limb-sparing techniques have been developed,including tumor prosthesis, allograft, autograft, and graft-prosthesis composite.However, each of these methods has its short-and long-term disadvantages, such as nonunion, mechanical failures and poor limb function (limb lengthdiscrepancy). The technique of intracorporeal devitalization of tumor-bearingbone segment in situ by microwave ablation after separating it from surroundingnormal tissues with a safe margin is a promising biological method forlimb-salvage treatment, which might avoid some shortcomings encountered byabove-mentioned conventional methods. After in situ ablation, the biologicaloutcome of resultant devitalized tumor-bearing bone segment is poorlyunderstood. Clinical specimens might be useful for studying its healing potentialand process. However, the specimens retrieved without serious complicationsare rare and may have much greater heterogeneity, and these complicationsmight have altered the normal repair process. Therefore, in this study, firstly weplan to establish an animal model with its distal femur being devitalized in situby microwave ablation. Then, using different detection methods, we study andanalyze its healing potential and process at different time intervals. Furthermore,in an in vitro study, we also intend to detect the initial changes of mechanicalproperties of bone specimens after devitalized by microwave ablation in vitro.Methods: Firstly, we applied the microwave ablation to devitalize thedistal femur of dogs in situ. With a monopole microwave antenna, we couldproduce a necrotic area of nearly20mm in length. Then, many detectionmethods such as radiography, technetium-99m-methylene diphosphonate(99mTc-MDP) bone scintigraphy, microangiography, tetracycline fluorescencedouble labeling, histopathological examination, and functional evaluation wereperformed at2weeks,1,2,3,6,9, and12months postoperatively to assess thehealing process. As for in vitro mechanical study, devitalized bone segments,structurally either intact or reconstructed with bone cement in a defect, wereused for compression and three-point bending test to assess their mechanical properties.Results: In this study, we successfully established an animal model with itsdistal femur being devitalized by microwave in situ. At the end of the follow-up,the revascularization percentage and new bone mineral apposition rate wereclose to the normal level, and the functional outcome was excellent and good in20dogs (83.33%) and poor in four dogs (16.67%) that developed fracture.However, the results of radiography, bone scintigraphy, and histopathologicalexamination indicated that the devitalized bone segment had not finished in12months postoperatively. As for the in vitro mechanical test, there was nosignificant statistical difference in maximum compression and bending loadbetween the structurally intact control and microwave group, neither was theresignificant statistical difference between the reconstructed control andmicrowave group (P＞0.05).Conclusion: Our in vivo study showed that intracorporeally and in situdevitalized bone segment by microwave had a great revitalization potential. Invitro study revealed that the initial mechanical strength of the devitalized bonesegment might not be affected by microwave ablation. Therefore, our resultssuggest that intracorporeal devitalization of tumor-bearing bone segment in situis a useful method for limb-salvage treatment, both in biological and mechanicalterms.