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The incidence of arthroscopic surgery has increased over the past two decades, and arthroscopic shaver systems have become a widely used orthopedic instrument. However, most razors are generally not sharp enough, easy to wear, and so on. The purpose of this article is to investigate the structural characteristics of the new double serrated blade of the BJKMC (Bojin◊ Kinetic Medical) arthroscopic razor. Provides an overview of the product design and validation process. The BJKMC arthroscopic razor features a tube-in-tube design, consisting of a stainless steel outer sleeve and a rotating hollow inner tube. The outer shell and inner shell have corresponding suction and cutting ports, and there are notches on the inner and outer shells. To justify the design, it was compared to a Dyonics◊ Incisor◊ Plus insert. Appearance, tool hardness, metal tube roughness, tool wall thickness, tooth profile, angle, overall structure, critical dimensions, etc. were checked and compared. working surface and a harder and thinner tip. Therefore, BJKMC products can work satisfactorily in surgery.
A joint in the human body is a form of indirect connection between bones. They are a complex and stable structure that plays an important role in our daily life. Some diseases alter the load distribution in the joint, resulting in functional limitation and loss of function1. Traditional orthopedic surgery is difficult to accurately treat minimally invasive, and the recovery period after treatment is long. Arthroscopic surgery is a minimally invasive procedure that requires only a small incision, causes less trauma and scarring, has a faster recovery time, and fewer complications. With the development of medical devices, minimally invasive surgical techniques have gradually become a routine procedure for orthopedic diagnosis and treatment. Shortly after the first arthroscopic knee surgery, it was officially adopted as a surgical technique by Kenji Takagi and Masaki Watanabe in Japan2,3. Arthroscopy and endoprosthetics are two of the most important advances in orthopedics4. Today, minimally invasive arthroscopic surgery is used to treat a variety of conditions and injuries, including osteoarthritis, meniscal injuries, anterior and posterior cruciate ligament injuries, synovitis, intra-articular fractures, patellar subluxation, cartilage and loose body lesions.
The incidence of arthroscopic surgery has increased over the past two decades, and arthroscopic shaver systems have become a widely used orthopedic instrument. Currently, surgeons have a variety of options available to surgeons, including cruciate ligament reconstruction, meniscus repair, osteochondral grafting, hip arthroscopy, and facet joint arthroscopy, depending on the preference of the surgeon1. As arthroscopic surgical procedures expand to more joints, physicians can examine synovial joints and surgically treat patients in previously unimaginable ways. At the same time, other tools were developed. They usually consist of a control unit, a handpiece with a powerful motor and a cutting tool. The dissection instrument allows for simultaneous and continuous suction and debridement6.
Due to the complexity of arthroscopic surgery, multiple instruments are often required. The main surgical instruments used in arthroscopic surgery include arthroscopes, probe scissors, punches, forceps, arthroscopic knives, meniscus blades and razors, electrosurgical instruments, lasers, radio frequency instruments and other instruments 7.
The razor is an important tool in surgery. There are two main principles of arthroscopic surgery pliers. The first is to remove remnants of degenerated cartilage, including loose bodies and floating articular cartilage, by suctioning and flushing the joint with copious saline to remove intra-articular lesions and inflammatory mediators. The other is to remove the articular cartilage separated from the subchondral bone and repair the worn cartilage defect. The torn meniscus is excised and a worn and broken meniscus is formed. Razors are also used to remove some or all of the inflammatory synovial tissue, such as hyperplasia and thickening1.
Most minimally invasive scalpels have a cutting section with a hollow outer cannula and a hollow inner tube. They rarely have 8 serrated teeth for a cutting edge. Different blade tips provide different levels of cutting power to the razor. Conventional arthroscopic razor teeth fall into three categories (Figure 1): (a) smooth inner and outer tubes; (b) smooth outer tubes and serrated inner tubes; (c) serrated (which may be a razor blade)) inner and outer tubes. 9. Their sharpness to soft tissues increases. The average peak force and cutting efficiency of a saw of the same specification is better than a 10 flat bar.
However, there are a number of problems with currently available arthroscopic shavers. First, the blade is not sharp enough, and it is easy to block when cutting soft tissue. Second, a razor can only cut through soft synovial tissue—the physician must use a burr to polish the bone. Therefore, the blades need to be changed frequently during operation, which increases the operating time. Cut damage and razor wear are also common problems. Precision machining and accuracy control really formed a single evaluation index.
The first problem is that the razor blade is not smooth enough due to the excessive gap between the inner and outer blades. The solution to the second problem can be to increase the angle of the razor blade and increase the strength of the material of construction.
The new BJKMC arthroscopic razor with double serrated blade can solve the problems of blunt cutting edges, easy clogging and rapid tool wear. To test the practicality of the new BJKMC razor design, it was compared with Dyonics◊’s counterpart, the Incisor◊ Plus Blade.
The new arthroscopic razor features a tube-in-tube design, including a stainless steel outer sleeve and a rotating hollow inner tube with matching suction and cutting ports on the outer sleeve and inner tube. The inner and outer casings are notched. During operation, the power system causes the inner tube to rotate, and the outer tube bites with teeth, interacting with the cutting. The completed tissue incision and loose bodies are removed from the joint through a hollow inner tube. To improve cutting performance and efficiency, a concave tooth structure was chosen. Laser welding is used for composite parts. The structure of a conventional double tooth shaving head is shown in Figure 2.
In general design, the outer diameter of the anterior end of the arthroscopic shaver is slightly smaller than the posterior end. The razor should not be forced into the joint space, because both the tip and the edge of the cutting window are washed out and damage the articular surface. In addition, the width of the shaver window should be large enough. The wider the window, the more organized the shaver cuts and sucks, and the better it prevents clogging of the window.
Discuss the effect of tooth profile on cutting force. The 3D model of the razor was created using SolidWorks software (SolidWorks 2016, SolidWorks Corp., Massachusetts, USA). The outer shell models with different tooth profiles were imported into the finite element program (ANSYS Workbench 16.0, ANSYS Inc., USA) for meshing and stress analysis. Mechanical properties (modulus of elasticity and Poisson’s ratio) of materials are given in Table. 1. The mesh density used for soft tissues was 0.05 mm, and we refined 11 planer faces in contact with soft tissues (Fig. 3a). The entire model has 40,522 nodes and 45,449 meshes. In the boundary condition settings, we fully constrain the 6 degrees of freedom given to the 4 sides of the soft tissues and the razor blade is rotated 20° around the x-axis (Fig. 3b).
An analysis of three razor models (Fig. 4) showed that the point of maximum stress occurs at a structural abrupt change, which is consistent with the mechanical properties. The razor is a disposable tool4 and there is little risk of blade breakage during single use. Therefore, we mainly focus on its cutting ability. The maximum equivalent stress acting on soft tissue may reflect this characteristic. Under the same operating conditions, when the maximum equivalent stress is the largest, it is preliminarily considered that its cutting properties are the best. In terms of soft tissue stress, the 60° tooth profile razor produced the maximum soft tissue shear stress (39.213 MPa).
Shaver and soft tissue stress distribution when razor sheaths with different tooth profiles cut soft tissues: (a) 50° tooth profile, (b) 60° tooth profile, (c) 70° tooth profile.
To justify the design of the new BJKMC blade, it was compared with an equivalent Dyonics◊ Incisor◊ Plus blade (Fig. 5) that has the same performance. Three identical types of each product were used in all experiments. All used razors are new and undamaged.
Factors that affect razor performance include the hardness and thickness of the blade, the roughness of the metal tube, and the profile and angle of the tooth. To measure the contours and angles of the teeth, a contour projector with a resolution of 0.001 mm was chosen (Starrett 400 series, Fig. 6). In experiments, shaving heads were placed on a workbench. Measure the tooth profile and angle relative to the crosshairs on the projection screen and use a micrometer as the difference between the two lines to determine the measurement. The actual tooth profile size is obtained by dividing it by the magnification of the chosen objective. To measure a tooth angle, align the fixed points on either side of the measured angle with the sub-line intersection on the hatched screen and use the angle cursors in the table to take readings.
By repeating this experiment, the main dimensions of the working length (inner and outer tubes), anterior and posterior outer diameters, window length and width, and tooth height were measured.
Check the surface roughness with a pinpointer. The tip of the tool is moved horizontally above the sample, perpendicular to the direction of the processed grain. The average roughness Ra is obtained directly from the instrument. On fig. 7 shows an instrument with a needle (Mitutoyo SJ-310).
The hardness of razor blades is measured according to the Vickers hardness test ISO 6507-1:20055. The diamond indenter is pressed into the surface of the sample for a given period of time under a certain test force. Then the diagonal length of the indentation was measured after the removal of the indenter. Vickers hardness is proportional to the ratio of the test force to the surface area of the impression.
The wall thickness of the shaving head is measured by inserting a cylindrical ball head with an accuracy of 0.01 mm and a measurement range of approximately 0-200 mm. The wall thickness is defined as the difference between the outer and inner diameters of the tool. The experimental procedure for measuring the thickness is shown in Fig. 8.
The structural performance of the BJKMC razor was compared with that of a Dyonics◊ razor of the same specification. The performance data for each part of the product is measured and compared. Based on the dimensional data, the cutting capabilities of both products are predictable. Both products have excellent structural properties, a comparative analysis of electrical conductivity from all sides is still required.
According to the angle experiment, the results are shown in Table 2 and Table 3. The mean and standard deviation of the profile angle data for the two products were not statistically different.
A comparison of some key parameters of the two products is shown in Figure 9. In terms of inner and outer tube width and length, Dyonics◊ inner and outer tube windows are slightly longer and wider than those of BJKMC. This means the Dyonics◊ can have more room to cut and the tubing is less likely to clog. The two products did not differ statistically in other respects.
The parts of the BJKMC razor are connected by laser welding. Therefore, there is no external pressure on the weld. The part to be welded is not subject to thermal stress or thermal deformation. The welding part is narrow, the penetration is large, the mechanical strength of the welding part is high, the vibration is strong, the impact resistance is high. Laser-welded components are highly reliable in assembly14,15.
Surface roughness is a measure of the texture of a surface. The high-frequency and short-wave components of the measured surface, which determine the interaction between the object and its environment, are considered. The outer sleeve of the inner knife and the inner surface of the inner tube are the main working surfaces of the razor. Reducing the roughness of the two surfaces can effectively reduce the wear on the razor and improve its performance.
The surface roughness of the outer shell, as well as the inner and outer surfaces of the inner blade of two metal tubes, was obtained experimentally. Their average values are shown in Figure 10. The inner surface of the outer sheath and the outer surface of the inner knife are the main working surfaces. The roughness of the inner surface of the scabbard and the outer surface of the BJKMC inner knife is lower than similar Dyonics◊ products (same specification). This means that BJKMC products can have satisfactory results in terms of cutting performance.
According to the blade hardness test, the experimental data of two groups of razor blades are shown in Figure 11. Most arthroscopic razors are made of austenitic stainless steel due to the high strength, toughness and ductility required for razor blades. However, BJKMC shaving heads are made from 1RK91 martensitic stainless steel. Martensitic stainless steels have higher strength and toughness than austenitic stainless steels17. The chemical elements in BJKMC products meet the requirements of S46910 (ASTM-F899 Surgical Instruments) during the forging process. The material has been tested for cytotoxicity and is widely used in medical devices.
It can be seen from the results of the finite element analysis that the stress concentration of the razor is mainly concentrated on the tooth profile. IRK91 is a high-strength supermartensitic stainless steel with high toughness and good tensile strength at both room temperature and elevated temperature. The tensile strength at room temperature can reach more than 2000 MPa, and the maximum stress value according to the finite element analysis is about 130 MPa, which is far from the fracture limit of the material. We believe that the risk of blade fracture is very small.
The thickness of the blade directly affects the cutting ability of the razor. The thinner the wall thickness, the better the cutting performance. The new BJKMC razor minimizes the wall thickness of two opposing rotating bars, and the head has a thinner wall than its counterparts from Dyonics◊. Thinner knives can increase the cutting power of the tip.
The data in Table 4 shows that the wall thickness of the BJKMC razor measured by the compression-rotation wall thickness measurement method is smaller than that of the Dyonics◊ razor of the same specification.
According to comparative experiments, the new BJKMC arthroscopic razor showed no obvious design differences from the similar Dyonics◊ model. Compared to Dyonics◊ Incisor◊ Plus inserts in terms of material properties, BJKMC double tooth inserts have a smoother working surface and a harder and thinner tip. Therefore, BJKMC products can work satisfactorily in surgery. This study was designed prospectively and specific performance needs to be tested in subsequent experiments.
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This study did not receive specific funding from any funding agencies in the public, commercial, or non-profit sectors.
School of Medical Devices and Food Engineering, Shanghai University of Technology, No. 516, Yungong Road, Shanghai, People’s Republic of China, 2000 93