Study On The Microwave Therapy For The Post-operation With Titanium Alloy Implants

Due to the high incidence of traumatic bone disease, the postoperative recovery of patients has become a research focus. In the last few years, orthopaedic metal internal fixation has been developed rapidly, which was of wide application in clinic. However, patients always suffer from complications, such as postoperative radiation pain, heterotopic ossification, joint degeneration and so on. It is known that reasonable application of physical treatment might promote healing of fractures and the motor function recovery. But one of the contraindications for microwave treatment listed in the literature is surgically implanted metal plates in the treatment field. With the development of medical metallic materials, implants of titanium alloy are widely used clinically. Conventional theory in physiotherapy indicated that microwave exposure causes heat damage to the tissues adjacent to metal implants. However, for its inherent characteristics of low electrical and thermal conductivity, application of titanium alloy is challenging the theory. The current studied aimed to experimentally test the feasibility of microwave treatment on the lamb with titanium alloy implants in vitro and in vivo and to provide the evidence to the microwave theory. The study was constituted by 3 parts.Part I The Influence of Metal Material in the Treatment Field on Microwave Thermal Effect in vitroObjective Microwave belongs to the ultra high frequency electromagnetic wave. Its radiation area can form strong electromagnetic fields. The metal exposure on the microwave irradiation would be heat since the eddy current, hysteresis and some other reasons, which might cause heat injure adjacent to the metal. Previously, it is reported that there might be relationship between properties of materials and temperature rise of metal in the field. The present research studied the temperature changes of medical metal under medical microwave irradiation. The aim of the research was to reveal the influence of metal material on microwave thermal effect.Methods Five kinds of implants made of titanium, titanium alloy, copper, nickel, austenitif stainless steel were embedded at a 1 cm depth of tissue-equivalent agar-phantom. The phantom was placed vertical to 2450 MHz microwave applicator. Temperature rise of phantom adjacent to the titanium alloy were measured under exposure to powers-gradient microwave radiation from 20 W to 60 W. A scatter diagram and the trend line fitting analyses were conducted to examine the characteristics and trends of temperature rise and electrical conductivity.Results The peak temperature of titanium ally were 0.4 ± 0.12 ℃, 0.5 ± 0.11 ℃ and 1.7 ± 0.12 ℃ at 20 W-, 40 W-, and 60 W- microwave irradiation respectively, which was the lowest temperature rise in five kinds of metals. The highest temperature rises were found in phantom adjacent to copper, which were of 0.5 ± 0.13 ℃, 3.7 ± 0.12 ℃ and 3.8 ± 0.14 ℃ at three powers of microwave irradiation. Under 20 W microwave irradiation, linear regression demonstrated no relation between temperature rise and electrical conductivity( R=-0.32,P= 0.364;R=-0.27,P= 0.452, at 15 min and 30 min respectively). However, there were positive correlation between temperature rise and electrical conductivity under 40 W( R= 0.55,P= 0.057;R= 0.66,P= 0.038, at 15 min and 30 min, respectively). Temperature rise and electrical conductivity were highly linearly correlated at 60 W( R= 0.68,P= 0.032;R= 0.74,P= 0.015, at 15 min and 30 min respectively).Conclusion Under the 2450 MHz microwave irradiation, metal temperature rise related to metal material, and temperature of titanium alloy with lowest electrical conductivity changed smallest in five metals. Microwave might become a physical therapy after titanium alloy implantation.Part II The influence of a single microwave radiation on tissues adjacent to titanium alloy: an animal experimental experimentObjective In the above part of research, it was found titanium alloy brought lowest effects to uniformity of the thermal field by microwave irradiation in five kinds of metals. Since the limitation of study in vitro, a further research on animals about the influence of microwave to the limbs with titanium alloy has been taken.Methods New Zealand white rabbits were implanted with titanium alloy internal fixation plates. Femurs were exposed to 20, 40, 60, or 80 W of microwave radiation for 30 min(microwave applicator at 2450 MHz), and temperatures of the implants and muscles adjacent to implants were recorded. To evaluate thermal damage, nerves were electro diagnostically assessed immediately after radiation, and histological studies performed on nerve and muscle sections.Results As expected, implant temperature was highest in the exposure field. Compared to the control limbs, temperatures of limbs with titanium alloy implants increased significantly at 60 and 80 W(6.1 ± 0.5 °C vs. 9.2 ± 0.3 °C at 60 W; 7.0 ± 0.9 °C vs. 14.8 ± 0.7 °C at 80 W), with a significant decline in the nerve conduction velocity(declined by 29.0 % at 60 W and 60.6 % at 80 W vs. control limbs) and acute thermal injuries in nerves and muscles adjacent to implants. However, temperature remained unchanged and no adverse effects were observed in nerves and muscles at 20 and 40 W.Conclusion Hence, temperature remained unchanged and no adverse effects were observed in nerves and muscles at 20 and 40 W, but 60 and 80 W did. We believe that a lower powes(20 – 40 W) of continuous wave microwave irradiation is safe for limbs with titanium alloy implants.Part III The short course of treatment effect and safety of small power of microwave on fracture with titanium alloy internal fixationObjective: In the above part we found that 20 – 40 W continuous wave microwave irradiation was safe for limbs with titanium alloy implants for one time treatment. The aim of this part of the study was to evaluate the security and therapeutic effects of low powers microwave on healing of a fracture with titanium alloy internal fixation.Methods Using scroll saw, a 3.0 mm bone defect was created in the middle of thigh bone in 12 New Zealand white rabbits. Titanium alloy internal fixation systems were implanted in rabbits. Rabbits in treatment group began to received microwave treatment(2,450 MHz, 25 W, 10 min per day) 3 days after operation. Normalized radiographic density of the fracture gap was measured on the 10 th day and 30 th day of the microwave treatment. All of the animals were killed after 30 days microwave treatment, and then histological and histomorphometric examinations were performed on the harvested muscles, nerves and bone tissues. The expression of caspase-3,-9 was analyzed by realtime-PCR and Western blot.Results No abnormal morphological changes were investigated in nerve and bone around the implants of microwave treatment group. But some reversible damages were observed occasionally in muscles, including swelling myocytes with light microscopy and mitochondrial swelling with transmission electron microscopy. The expression of caspase-3,-9 didn’t rise significantly(both P > 0.05). Radiographic assessments showed that fracture healing was accelerated especially on the 10 th day of the microwave treatment(P < 0.05). The differences in the mean histological grade of callus between implanted control group and microwave treated group were statistically significant(P = 0.0302 at 10 th day and P = 0.0413 at 30 th day, respectively) Histomorphometric examinations also revealed an improvement in the healing bones.Conclusion Low power microwave(2450 MHz, 25 W, 10 min/d, 30 d) treatment brings no heat damage for the fracture with titanium alloy internal fixation, and improves the fractures healing in rabbits. Our results suggest that, in the healing of fracture with titanium alloy internal fixation, a low power of microwave treatment may be a promising method.