CHAPTER 66 Current Controversies

Robotics for Total Hip Arthroplasty

M.A. Hafez, B. Jaramaz, A.M. DiGioia, III

Robotic surgical techniques have become a reality, and their clinical applications are expanding in many surgical specialties. In addition to orthopedics, robotic techniques have been clinically used in cardiothoracic surgery, urology, gastrointestinal surgery, oncology, pediatric surgery, gynecology, and others. Some authors (Hashizume)¹ envisaged that robotic techniques could be applied to almost all surgical procedures in the future. The number of surgical robots in use and under development is significant. Pott and colleagues² identified 159 surgical robots with different mechanisms and functions. These can be classified according to their tasks, mechanism of action, degree of freedom, and level of activity. For the purpose of simplicity, orthopedic robots can be categorized as industrial (large), hand-held, or bone-mounted robots.

There are distinct differences between orthopedic robots and other surgical robots. The dominant type of surgical robot is the master-slave mechanism that translates the surgeon’s hand motions to the robotic arms that manipulate surgical instruments, for example, the DaVinci robot (Intuitive Surgical, Sunnyvale, CA). The main functions of surgical robots are the elimination of tremors and the scaling of motion (refining and/or reinforcing), thus improving accuracy and precision. Conversely, orthopedic robots act directly on bone, performing mechanical actions such as milling, drilling, and cutting. The average cost of a surgical robot may exceed $1,000,000, and its maintenance cost may reach $100,000 per year.^3,⁴ In orthopedics, Honl and colleagues⁵ estimated the additional cost of using ROBODOC (Integrated Surgical Systems Sacromento, CA) in total hip arthroplasty (THA) to be $700 per case, which did not include the cost of additional operating room time.

In orthopedics the use of computer-enabled technology is not confined to robotics. Computer-assisted orthopedic surgery (CAOS) has become an active field of research, development, and clinical testing that involves the use of a number of tools and actions such as preoperative planning, simulation, robotic surgery, intraoperative guidance, telesurgery, and training. Hafez and colleagues ⁶ grouped CAOS devices on the basis of their functionality and clinical use into six categories (robotics, navigation, hybrid, templating, simulators, and telesurgery), which are then subgrouped on a technical basis. Robotics and navigation have already been used in many different clinical applications. The main difference between robotic and navigation systems is the mode of action: robotic systems involve a robotic device that can perform a part or all of the surgical procedure. In orthopedics, robotics began to be used first in the early 1990s, when ROBODOC was used for femoral canal preparation (milling) in total hip arthroplasty (THA).^6a Few other robotic systems have been developed for orthopedic use and tested clinically, most notably CASPAR,⁷ and Acrobot.⁸ Robotic systems typically require preoperative CT scans and intraoperative registration to correlate the patient anatomy to preoperative images. They also need rigid fixation of the limb and the robot. On the other hand, navigation systems are passive and act as information systems guiding the surgeon and providing the information necessary to control and perform the procedure.

Although computer-assisted techniques started first in neurosurgery, orthopedics is now leading the way, with total knee arthroplasty being the most common procedure aided by these technologies. The clinical applications have also expanded in various subspecialties, particularly arthroplasty, trauma, and spinal surgery. However, the use of computer-assisted technologies in general is still under debate owing to the cost, complexity, and long operative time associated with the use of such systems. Current navigation techniques require the insertion of tracking targets into bone, and robotics require rigid fixation of the limb, thus adding invasiveness and risk. All of these considerations contribute to the cautious environment in the adoption of these new technologies. Comprehensive cost-effectiveness analysis may be required before these emerging technologies are widely accepted.

RATIONALE AND INDICATIONS

The development and application of a wide range of computer-assisted techniques in orthopedics could be attributed to the nature of the skeletal system. Because of their relative rigidity, bony structures maintain the same shape before, during, and after surgery, which enables the use of preoperative images, precise surgical planning, and registration. Orthopedic surgical procedures are reconstructive in nature and involve mechanical actions such as cutting, drilling, reaming, and fixation. The demand for a high degree of accuracy and reproducibility, which is not always met by conventional techniques, has paved the way for CAOS applications.

THA is one of the most important orthopedic procedures of the last century. In the United States alone, more than 170,000 THA procedures are performed every year, and the rate is steadily increasing. It is a demanding procedure, and technical errors can affect the function and the survival of the implants. Technical errors and outliers still occur and may jeopardize survival and function. Malalignment of implants is the major contributing factor for dislocations.^9,¹⁰ In addition, malalignment of the acetabular component increases the occurrence of impingement and dislocation, which in turn reduces the range of motion and increases the risk of wear and failure.

LIMITATIONS OF THE CURRENT TECHNIQUES IN TOTAL HIP ARTHROPLASTY

Current surgical techniques lack quantitative preoperative planning and sensitive tools to measure intraoperative surgical performance and patients’ outcomes. Current techniques cannot link preoperative plans with the execution of the surgical task or link the surgical performance to postoperative outcome.¹⁰ Conventional tools do not provide real-time feedback or accurate information during surgery.

Most surgeons still rely on freehand techniques or mechanical guides to align THA implants (the acetabular cup in particular). Yet these techniques have limited accuracy. Saxler and colleagues ⁹ assessed the accuracy of freehand cup positioning in 105 THA procedures using a CT-based navigation system as a measurement tool. Only 27 of 105 THAs were positioned within the safe zone as defined by Lewinnek and colleagues.¹¹ The intraoperative motion of the pelvis is also a possible cause for acetabular cup malalignment.⁹

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