Surgical site infection related to orthopaedic implants is one of the serious complications. In the previous works, we developed a novel thermal spraying technology combined silver with hydroxyapatite (HA) in order to resolve such problems, and reported the property and antibacterial effect of them in vitro. However, no previous reports have investigated in vivo. Therefore, we monitored serum silver level in rats to clarify in vivo kinetics of silver released from the coating.

HA loaded with 3 wt % of silver oxide (HA-Ag) and plain HA powder were sprayed on surface of titanium disks (20 mm diameter × 1 mm thick) by the flame spraying, which is a kind of thermal spraying method with acetylene torch. All these test pieces were obtained from Japan Medical Materials Corporation (JMM, Osaka, Japan). Both samples were implanted singly into the back subcutaneous pockets of male Sprague-Dawley rats (150–200 g). Rats were housed individually and given ad libitum access to food and water. After 24 h, 48 h, 7 d, 14 d and 28 d, the rats were sacrificed, and then the blood was drawn from common iliac vein. All procedures were operated under anesthesia. These blood samples were spun down and serum silver levels were measured by an inductively coupled plasma mass spectrometry.

The average serum silver level in HA-Ag group had increased to more than 40 ppb until 48 h after implantation, and then decreased rapidly to normal level. There were significant differences (p < 0.05) between HA-Ag and HA group, at each measurement period.

This is the first report to elucidate the serum silver level in rats implanted HA-Ag coatings. To date, reported coating technologies have included direct-loading antibacterial agents or heavy metals including silver with prosthesis base. The combine technology HA with silver would be effective in not only antibacterial but also osteoconductive respect. Our experimental results highlight the following 2 features: the serum silver levels peaked relatively early, and the levels reduced immediately to normal level after the peak. Therefore, we speculate that the released silver would not be accumulated generally, which not contribute long-term toxicity, and the coating would be suitable for prevention of early surgical site infections.

This study provides novel and important information on in vivo release- property for HA-Ag coating, and suggests this coating is effective against not late but rather early infection related to orthopaedic implants.

Bacterial infections related to orthopaedic implants is one of the serious types of complications. Recently, there has been a greater interest in antibacterial biomaterials. However, antibacterial evaluations of each material are inconsistant, so intercomparison of the antibacterial performance is difficult. This study focused on the Japanese Industrial Standards test (JIS Z2801), which is used for antibacterial evaluation of commodities. The study investigated a suitable evaluation method for in vitro antibacterial activity of biamaterials. In 2007, JIS Z2801 test was approved as international standard ISO 22196.

Hydroxyapatite (HA) powder containing 3 wt % of silver oxide (Ag) was sprayed on the surface of titanium disks with the thermal spraying method, using an acetylene torch. This coating has been proved to generate strong antibacterial activity in previous studies. The antibacterial activity was examined with the JIS Z 2801 test and modified JIS Z2801 test. The bacterial strains used in JIS Z2801 test were Escherichia coli (E.coli), Staphylococcus aureus (S.aureus). Bacterial culture medium was instilled onto the surface of the test disks (about 106 cells/ml) and covered with polystyrene films. After cultivation in 1/500 Nutrient Broth for 24 h at 35°C, the bacteria was washed out with the broth. The numbers of viable bacteria in the broth were counted with the agar plate culture method. Additionally, Modified JIS Z2801 test was performed. Modified points were added to the bacterial strain of biofilm-forming methicillin-resistant S.aureus (BF-MRSA), using Fetal Bovine Serum (FBS) as a culture medium, and cultivated at 37°C.

In the JIS Z2801 test, Antibacterial activity values of the HA-Ag disk were composed against E.coli 4.1 and S.aureus 5.0. In the modified JIS Z2801 test, antibacterial activity values against E.coli, S.aureus and BF-MRSA were 8.2, 5.5, and 7.1. When this value is greater than 2.0, it shows there is antibacterial activity. The titanium disk coated with HA-Ag showed antibacterial activity in both tests.

The JIS Z2801 test is designed to evaluate comodities in poor nutritional environment. However, the environment in the body is eutrophic. It is easy to make bacterial growth. For this reason, it is necessary to consider evaluating for biomaterials with suitable method considered in vivo. In this study, to examine the condition like that found in the body, we cultivated FBS at 37°C. In addition, the antibacterial activity against BF-MRSA was examined to consider the bacterial infection related to orthopaedic implants. The modified JIS Z2801 test showed that it is a suitable evaluation method for in vitro antibacterial activity of biomaterials.

In the case of a complete dislocated hip or a severe deformity of the proximal femur, total hip arthroplasty (THA) can still be combined with a proximal femoral osteotomy for shortening femur or correcting the deformity if needed. Subtrochanteric femoral shortening and a corrective osteotomy are considered to be an integral part of THA for such cases. A precise osteotomy is mandatory to achieve good results. Although, the freehand excision of V-shaped subtrochanteric osteotomy used to be performed frequently, this procedure was also subject to some pitfalls, such as poor coaptation of the osteotomy surface. A new device was thus developed to perform a V-shaped osteotomy in an identical central axis between the distal and proximal femur. The purpose of this study was to evaluate the efficacy of the device by comparing the perioperative results with those of a free-hand subtrochanteric osteotomy.

From 1999 to 2002, THA combined with a double-chevron subtrochanteric osteotomy was performed by free hand (free hand group). From 2003 to 2007, THA combined with a double-chevron subtrochanteric osteotomy was performed using a new device (device group). The free hand group included 27 hips in 21 patients. The mean age of the patients (23 females and 3 males) at the time of the operation was 58 years. Fourteen were completely dislocated hips and 13 followed various proximal femoral osteotomies. The device group included 102 hips in 79 patients. The mean age of thepatients (70 females and 9 males) at the time of the operation was 62 years. Seventy two were completely dislocated hips and 26 followed various proximal femoral osteotomies. Four parameters were used to evaluate the efficacy of the device:

operation time,

The mean operation time, total blood loss, and C-reactive protein in the device group all significantly decreased in comparison to the free hand group. The decreases ranged from; 132 to 96 minutes (p< 0.01), 1346 to 999 g (p< 0.01), 4.9 to 3.0 mg/dl (p< 0.05), respectively. Two types of complications were observed at the osteotomy site. Pseudoarthrosis at the osteotomy site was observed one case in each group and both of these cases underwent a stem revision (4% in the freehand group and 1% in the device group). A femoral shaft split was observed in 3 cases in the freehand group (11%) and 3 cases in the device group (3%) and all 6 cases were treated conservatively. There were no instances of nerve palsy, infections, or thromboembolic events resulting from these procedures.

The above described new device allowed for the easy and accurate performance of a subtrochanteric V-shaped osteotomy with THA for either a completely dislocated hip or a severely deformed proximal femur.