Microwave radiation is defined as that with a frequency of 300 MHz-300GHz, which lies on the electromagnetic spectrum between radiofrequency (RF) and infrared radiation. In general, microwaves could be focused to produce physiological heating in deep body, for example, increased temperature over 40°C [
1], increased blood flow [
2,
3], decreased pain [
4], and alterations in the physical properties of fibrous tissues [
5,
6]. The clinical application of microwaves improved range of motion in joints, and accelerated the resolution of hematoma and fracture healing [
7]. Microwave treatment is also used in the cure and rehabilitation of injuries and chronic inflammation of bone [
6,
8‐
12], joint [
13,
14], muscle and tendon [
15,
16]. Frequencies historically used in the rehabilitation were 2450[
17], 915 [
6,
18‐
22], 434 (with surface cooling) [
6,
20] and 27.12 MHz [
23]. The efficacy of an electromagnetic wave device depends on the target site and temperature.
Surgically implanted metal plates, screws, and pins in the treatment field are an absolute contraindication for microwave application [
8]. It is thought that electromagnetic radiation generated by microwave diathermy can be reflected, refracted or transmitted at the interface between tissues and metal implants [
8,
24], resulting in rapid elevation in temperature and tissue damage locally [
25‐
29]. However, some doctors believed that this contraindication appeared to be based on “common sense” and consensus rather than evidence-based practice, in vivo. Titanium implants are widely used clinically since titanium ion is non-magnetic [
30,
31]. It has a lower magnetic permeability and electric conductivity than common magnetic materials, and consequently less absorption of radio frequency (RF) [
32]. The findings from studies in vitro indicated that the temperature changes of titanium and titanium alloys in RF electromagnetic field were lower compared with other metallic implants [
27,
33]. In fact, the safety of shortwave diathermy has been proven in clinical case reports. Seiger [
34] applied pulsed shortwave diathermy (27.12 MHz, 800 pps, 400 microseconds (48 W), 20 min) over a patient’s ankle with orthopedic metal implants, resulting in improved ankle range of motion (ROM). No complaints of discomfort, pain, or burning sensation occurred. Another report similarly suggested no negative effects during the short-term follow-up [
35]. However, muscle temperature in the thigh was not monitored during the treatment. Although the patients’ complaints determined the temperature increase to some degree, a huge difference existed between thermal pain threshold and hyperthermia-induced injury [
6,
36]. As temperature measurement entailed an invasive approach, we designed an animal experiment to observe the transient temperature changes adjacent to the implants. Additionally, previous research involving RF electromagnetic field derived from mobile phones rarely indicated any risk associated with implants, though frequencies of 900[
29], 1800 [
28] and 2450 MHz [
37,
38] enhanced specific absorption rates (SAR). Therefore, the current study was based on the assumption that no dramatic temperature increases occurred in tissues around titanium alloy implants with a common therapeutic dose of microwave radiation (20-60w) used in rehabilitation.
Evidence supporting temperature changes in the tissues adjacent to the implants under microwave therapy is limited. In the current research, we modeled the worst possible cases of the most common implants under microwave irradiation in the rehabilitation of bone and muscle injuries. We implanted a titanium alloy into the femur of rabbit. We employed the highest frequency of 2450 MHz microwave generators at a treatment dose gradient of 20 w to 60 w, which are clinically used in rehabilitation. Temperature changes of muscles adjacent to the implants were recorded during the microwave exposure. Our objective was to determine the influence of microwave exposure on the temperature in tissues adjacent to a titanium alloy and the safety profile of microwave therapy.