The Healing Process of Intracorporeally and In Situ Devitalized Distal Femur by Microwave in a Dog Model and Its Mechanical Properties In Vitro

Background: Limb-salvage surgery has been well recognized as a standard treatment and alternative to amputation for patients with malignant bone tumors. Various limb-sparing techniques have been developed including tumor prosthesis, allograft, autograft and graft-prosthesis composite. However, each of these methods has short- and long-term disadvantages such as nonunion, mechanical failures and poor limb function. The technique of intracorporeal devitalization of tumor-bearing bone segment in situ by microwave-induced hyperthermia after separating it from surrounding normal tissues with a safe margin is a promising limb-salvage method, which may avoid some shortcomings encountered by the above-mentioned conventional techniques. The purpose of this study is to assess the healing process and revitalization potential of the devitalized bone segment by this method in a dog model. In addition, the immediate effect of microwave on the biomechanical properties of bone tissue was also explored in an in vitro experiment. Methods: We applied the microwave-induced hyperthermia to devitalize the distal femurs of dogs in situ. Using a monopole microwave antenna, we could produce a necrotic bone of nearly 20 mm in length in distal femur. Radiography, bone scintigraphy, microangiography, histology and functional evaluation were performed at 2 weeks and 1, 2, 3, 6, 9 and 12 months postoperatively to assess the healing process. In a biomechanical study, two kinds of bone specimens, 3 and 6 cm in length, were used for compression and three-point bending test respectively immediately after extracorporeall

The stiffness values of bone specimens in the microwave-treated and control groups.

<p>The stiffness values of bone specimens in the microwave-treated and control groups.</p

Revascularization percentage of devitalized bone segment at each time interval.

<p>At 2 weeks, there was no neovascularization in the cortical bone. At 1 month, the revascularization percentage was 3.78±1.99%, After then, the % revascularization increased rapidly to 18.65±4.44%, 43.12±5.89% and 68.66±13.20% at 2, 3 and 6 months respectively. While at 9 and 12 months, the percentage rose slowly up to 84.21±5.31% and 93.25±1.78% respectively.</p

Histological analysis about the healing process of intracorporeally devitalized bone segment.

<p>(<b>A–F</b>) Haematoxylin and eosin staining. (<b>A</b>) Necrotic cortex with empty osseous lacunae (arrow) at 2 weeks. (<b>B</b>) Coagulative necrotic tissues (asterisk) and acellular trabeculae (arrow) in bone marrow cavity at 2 weeks. (<b>C</b>) Initial infiltration of fibrovascular tissues (arrow) into the dead bone at 2 months after surgery. (<b>D</b>) Partial substitution of dead trabeculae by new woven bone (arrow) at 3 months. (<b>E</b>) Newly formed trabecuale (asterisk) at 9 months. (<b>F</b>) Remnants of dead trabeculae (asterisk) surrounded by amounts of fibrovascular tissues at 12 months. Scale bars: 100 µm.</p

Temperature changes over time at 5, 10, 15 and 20 mm away from the antenna.

<p>The temperatures at drill holes 5 mm and 10 mm away from the microwave antenna rose to >70°C at the time interval of 6 minutes and continued to be between 70 and 100°C thereafter. The temperatures at drill holes 15 and 20 mm away from the microwave antenna were kept below 70°C all the time.</p

Radiological analysis of intracorporeally and in situ devitalized bone segment.

<p>(<b>A</b>) Plain radiograph showed periosteal callus formation covering the entire cortical surface of the devitalized bone segment at 3 months. (<b>B</b>) Partial sclerosis still remained within the microwave-treated bone segment at 12 months.</p