1. Introduction

At present, computer assisted orthopedic surgery (CAOS) has become the hot topic of research in the computer field. It has been widely used in the precise surgery path, position targeting in surgery, minimally invasive surgery, non-invasive diagnosis and treatment, surgery simulation, remote surgery and etc.

Orthopedic surgery is one of the most common surgeries, but some patients’ post-operation effect is not satisfying. For example, in surgeries for long bone fracture, usually doctors will use intramedullary nails to fix the fractured bones, but the reposition of fractured bones and locking of the intramedullary nails are still big challenges for most of the doctors and even for clinical experts with sufficient experiences.

In surgeries for bone fracture, before fixation the primary work is the reposition of fractured bones. In traditional clinical surgery, doctors usually use auxiliary devices with limited degree of freedom to complete the reposition of fractured bones, and most of the devices have only the linear degree of freedom, so the effect of reposition is not satisfactory. Sometimes it needs two doctors to pull the two ends of the fractured bone, which largely relies on the clinical experience of doctors and requires great labor intensity.

The CAOS can markedly improve the precision, efficiency and stability. This article introduces a China-developed computer assisted orthopedic surgery system based on X-ray image navigation: HIT-RAOS. Its main function is to assist doctors to complete reposition of fractured bones and the locking of intramedullary nails.

2. Computer Robot System Design

The computer robot system consists of patient side, computer control system and doctor side.

The patient side is composed by operating bed, robot for reposition, precise X-ray apparatus, robot for navigation and auxiliary device.

The computer control system includes service control, control cabinet and image processing system.

The doctor side is formed by robot manipulator with force feedback, monitor and multi-media tools.

(1) Operating Bed

The operating bed is composed of base, bracket, thigh plate and calf plate, and according to the characteristic of human body is divided into two parts: left and right.

The operating bed has seven degrees of freedom including three degrees of freedom driven (X, Y and Z direction) by stepping motor, and four degrees of freedom without driven force such as the overturning of bed, the folding-down of the thigh plate, expansion of thigh plate and folding-down of the calf plate.

(2) Precise X-ray Apparatus

The image navigation technology is one of the crucial technologies of the system, i.e., conducting the operation and track control through visual feedback.

(3) Reposition Robot

Reposition robot system is to simulate the hand tact of traditional Chinese herbalist doctors to conduct the traction and reposition of fractured bones. Therefore the robot system is required to have the degree of freedom needed and the loading capacity, as well as high safety and reliability. Clinical investigation shows that the traction force for thigh bone is about 700N, so the loading capacity of the robot should be above 700N, and the robot need to have 6 degrees of freedom.

(4) Navigation Robot

After confirming the relative position of image space and operation space and posture, according to the mapping relation between the highly precise C-arm and the navigation robot in the coordinate system, doctors can conclude the position of robot relative to operation space and provide navigation.

The robot also has high precision and the repetitive position precision is within 0.03 mm. At the same time, the mobile precision of linear movement should be ensured on a satisfactory level.

(5) Remote Operation System

Frequent usage of X-ray apparatus and over-exposure to the X-ray will cause severe damage to medical staff and patients.

One of the most attractive characteristics of HIT-RAOS is that it adopts remote operating system. Doctors can remotely control the robot to complete the operation without worrying about the radiation of X-ray.

3. Registration and Surgery Planning System

After the reposition, doctors use specialized tools to insert the intramedullary nail into the marrow cavity and then use screw to lock the hole of the intramedullary nail with the bone.

Doctors will complete the surgery plan on the graphic interface and confirm the direction of traction force. They can calculate the hole position relative to navigation robot and orientation data on the processed X-ray image. The work of doctors becomes simple: just selecting steel-ball point of demarcating kit on the graphic planning interface and drawing lines on the interface.

4. Conclusion

This article systematically introduces HIT-RAOS. Chinese researchers have already successfully established this system and prove through experiments on human specimens that it can assist doctors to conduct orthopedic surgery, such as reposition and the locking of intramedullary nails.