Design and experimental force analysis of a novel elliptical vibration assisted orthopedic oscillating saw

https://doi.org/10.1016/j.medengphy.2018.02.005Get rights and content

Highlights

  • We designed a novel elliptical vibration assisted orthopedic oscillating saw to achieve a low cutting force under the condition of deepening cut depth and reducing cutting speed.

  • A kinematical analysis was performed on the elliptical vibration assisted orthopedic oscillating saw.

  • Elliptical vibration assisted sawing exhibited a smaller principle force and thrust force than conventional sawing.

  • The cutting forces are significantly reduced by increasing vibration frequency and vibration amplitude, and decreasing the sawing speed in current design.

Abstract

Orthopedic oscillating saws (OOSs) are widely used for plane processing in orthopedic surgery such as knee and hip replacement. However, sawing has been associated with bone breakthrough and necrosis problems. In this paper, a novel elliptical vibration assisted OOS was designed to achieve a low cutting force under the condition of deepening cut depth and reducing cutting speed, based on the analysis of brittle fractures of the bone and elliptical vibration assisted cutting kinematics. The elliptical vibration was generated using two parallel stacked piezoelectric actuators assembled with the fixture. In order to reduce the large cutting forces due to the large cutting depth, a series of experiments was also conducted to investigate the influence of processing parameters on cutting forces. It was demonstrated that cutting forces are significantly reduced by increasing the vibration frequency and vibration amplitude, and decreasing the sawing speed in the current design. The new design could minimize the cutting forces during sawing and allow surgeons to have better control over the sawing process.

Introduction

Orthopedic procedures such as osteotomies, and hip and knee joint replacements involve plane processing owing to the demand of implant assembly and fixation, for example, the surface to fixture interaction of the femoral component during total knee replacement. Orthopedic powered saws have been designed and widely used for plane processing since 1890s [1]. There are three main requirements for bone sawing: high efficiency, low temperature, and low cutting force. Considering the operation time of such a surgery, the high cutting efficiency is the most crucial factor for bone resection devices. One method to improve the cutting efficiency is to increase the cutting speed. OOS typically runs at 8000 to 20,000 oscillations per minute with relatively small oscillation angle (3° to 5°) [2]. However, the localized heat generation caused by the friction between the saw blade and bone increases with oscillation speed. High temperature, exceeding 47°C, will cause cellular damage and even cell necrosis [3], [4].

Increasing cutting depth with relatively low cutting speed has recently been suggested as a new method of enhancing cutting efficiency. Sugita and Mitsuishi [5], [6] proposed an orthogonal bone cutting method based on crack propagation characteristics at a large cutting depth that can enhance the cutting efficiency and precision. James et al. [7] designed an OOS with orbital blade motion for improving cutting efficiency and reducing temperature. Temperature was reduced owing to the short heat transfer time and large bone chips carrying more heat from the freshly sawed surface. The basic idea of orbital blade motion is similar to Sugita and Mitsuishi's method [5]. However, a large cutting depth, employed to perform high-efficiency excision and crack propagation, will generate a large cutting force, which may induce unnecessary damage, resulting in trauma and also making it difficult to be employed in manual surgery. Elliptical vibration assisted cutting (EVC), well known in high precision machining, has a high potential for reducing cutting forces [8], [9], [10], [11]. Furthermore, EVC could basically implement Sugita and Mitsuishi's orthogonal bone cutting method because the elliptical trajectory of the cutting tool is similar to the orthogonal method. However, EVC was often used for small cutting depths within 10 µm [12], [13], [14], [15]. The effect of EVC in a large cutting depth for bone sawing is still unclear, and there are few studies applying EVC in bone sawing. Hence, it is necessary to explore a design that combines EVC with bone sawing and to conduct a systematical analysis on the cutting forces during elliptical vibration assisted bone sawing with a large cutting depth.

In this study, a novel elliptical vibration assisted OOS was designed to carry out sawing with a relatively large cut depth in manual surgery, based on analyzing the bone crack propagation characteristics and kinematics of elliptical vibration assisted sawing. In order to understand the influence of processing parameters on cutting forces, systematical experimental analysis of forces in elliptical assisted sawing was performed on sawbones.

Section snippets

Principle of the elliptical vibration assisted sawing

Osseous tissue mainly can be divided into two groups: the cancellous bone and the cortical bone, with the latter being the hardest and anisotropic kind. The cortical bone has been found to have brittle properties when using a large cutting depth during orthogonal bone cutting, as shown in Fig. 1(a). When the cutting depth is in the range of 0–30 µm, a chip is generated continuously, as shown in Fig. 1(b). In Fig. 1(c), the chip presented as a discontinuous type. The brittle property of the

Experimental setup

In order to investigate the effect of the elliptical vibration assisted OOS, especially the cutting force during sawing, an elliptical vibration assisted OOS system has been designed and prepared as shown in Fig. 6(a) and (b). The sawing experiments were carried out on a precision servo system. The conventional oscillation was provided by an oscillator designed based on a crank-rocker mechanism, which is able to control the oscillation frequency (fo) from 0 to 50 Hz. The oscillation angle was

Results and discussion

The novel elliptical vibration assisted OOS has been designed to implement sawing at a relatively large cut depth, on the basis of analyzing the bone crack propagation characteristics and the kinematics of elliptical vibration assisted sawing. In order to control cutting forces in the actual surgery, experiments were implemented aiming to investigate the influence of vibration parameters and sawing parameters on cutting forces of elliptical vibration assisted OOS at a large cutting depth. The

Conclusions

In this paper, a novel elliptical vibration assisted orthopedic oscillating sawing system has been designed based on the crack propagation characteristics of the bone and elliptical assisted cutting mechanics. It is experimentally shown that low frequency elliptical vibration assisted sawing can be used for cutting bone, with advantages over the conventional sawing at a large cutting depth. A systematic experimental analysis has also been implemented in order to investigate the influence of

Competing interests

None declared.

Funding

No funding.

Acknowledgment

The authors thank Mr. Terashima and Mr. Hanami from TOKO Co., Ltd. for advice and discussion in the experiment.

References (22)

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