History of Computer-Assisted Knee Surgery and Evolution of Basic Concepts

Although a large volume of important work that became the foundation for computer-assisted knee surgery was being carried out throughout the 20th century, the initial clinical applications for knee surgery began in the 1980s.¹⁰⁹ In 1986, Kaiura, from the University of Washington presented a thesis on robotic-assisted total knee arthroplasty (TKA).^39,⁶² This work led to the design of one of the first computer robotic assistive systems for TKA, described by Matsen and colleagues⁸⁶ in 1993.¹³⁷ In the early 1990s, Kienzle and associates⁶⁵ and Stulberg¹³⁴ also described a computer-assisted robotic total knee replacement system. The desired position of the femoral and tibial cutting blocks was determined on a three-dimensional model derived from a computed tomography (CT) scan obtained preoperatively. The robot was secured to the operating table and to the bones and then positioned a drill to make holes for the pins over which the femoral and tibial cutting blocks were placed. The surgeon then performed the cuts with a standard oscillating saw. The accuracy of block placement with this system was within 1 mm and 1 degree. This work also introduced a method for determining the center of the femoral head by means of a kinematic registration technique. This technique was subsequently incorporated into all current navigation systems. Dynamic reference frames that were tracked by a camera were placed on the femur and the hip was put through a range of motion. The center of the sphere described during the circumduction maneuver represented the center of the femoral head.

By the early 1990s, the principles on which current computer-assisted total knee replacement systems are based had been established and validated, and important steps had been taken to identify how critical anatomic landmarks for knee surgery could be accurately acquired. It was, however, apparent to those working on these projects at that time, especially orthopedic surgeons, that robotic-based computer-assisted systems were too cumbersome, complex, and potentially too unsafe to be of substantial use to an active knee replacement surgeon in the foreseeable future.

Surgical navigation systems, however, appeared then to offer an attractive alternative to a field such as knee surgery, which could benefit from the accuracy provided by computer-assisted techniques without having to deal with the drawbacks and complexity of robots. These systems allowed intraoperative tracking of the position of the surgical tools and the bones to which they were attached. The surgeon, not a robot, could control all phases of the procedure.

The rapid evolution of surgical navigation systems to support the performance of knee surgery was made possible by the availability, in the early 1990s, of optical and electromagnetic tracking systems (Fig. 116-1). Optical tracking systems have played a special role in the development of surgical navigation systems for knee surgery because of their accuracy and reliability. These tracking systems, also referred to as optical localizers, have charge-coupled devices (CCDs, or cameras) mounted on a rigid frame. These cameras measure the position and orientation of multiple tracking markers, also called trackers, or rigid bodies. Each tracker incorporates a set of light-emitting diodes (LEDs), or reflective spheres, mounted in precise relative positions. These trackers can be affixed to bones, tools, and implants. The optical tracker is therefore able to monitor the precise position of these objects at any point during the surgical procedure.

Figure 116-1 A, Typical image-free computer-assisted hardware system consisting of an optical tracker with charged-coupled devices (CCDs—the cameras), computer monitor, control unit and processor, and foot control system for communication between the surgeon and the system. B, Active trackers (also called rigid bodies or fiducials) attached to bicortical screws rigidly fixed to the femur and tibia.

During the first half of the 1990s, a great deal of basic research was performed to develop surgical navigation systems using these optical tracking systems.¹⁰⁹ The first clinical applications incorporating these efforts began in 1995 in the field of spine surgery. Although these applications were based on the acquisition of anatomic information by means of preoperative imaging techniques, they were the basis for the development in the late 1990s of the image-free systems currently most widely used in knee surgery.

Four types of surgical navigation models are used in computer-assisted orthopedic surgery: (1) preoperative image–based (e.g., CT scans)^68,⁷⁵; (2) intraoperative image–based (e.g., fluoroscopy)^84,⁸⁵; (3) image-free; and (4) individual templating.^37,^75,^93,^112,¹³⁰ The anatomic information on which the surgical plan is made is acquired differently in each model. Although each model has its advantages and drawbacks, the image-free method for acquiring critical anatomic information has proved to be most amenable to the methods used currently to perform knee surgery. This method was first used clinically in 1993 to place grafts during anterior cruciate ligament (ACL) surgery.¹⁰⁹ Image-free navigation was subsequently applied to TKA surgery by Leitner and colleagues.⁸⁰ The first image-free computer-assisted TKA was performed in Grenoble, France, by Picard and associates in 1997.¹⁰⁷ The system used became the first commercially available image-free navigation system for knee reconstructive surgery (the OrthoPilot).¹⁰⁶ It identified critical anatomic landmarks using both kinematic (e.g., femoral circumduction, as described by Kienzle and coworkers in 1989⁶⁵) and surface registration techniques. Krackow and colleagues⁷⁴ subsequently developed surgical navigation systems based on these concepts. There are now a large number of image-free navigation systems available for use with almost every total knee system.

Although the foundations for the CAS systems currently being used in knee surgery began to be developed a century ago, actual systems available for clinical use have been available for less than 10 years. The rapid emergence of these systems suggests that current models will undergo substantial evolution and modification in the next few years.

Rationale For Use

Successful surgical reconstruction of the knee requires proper patient selection, appropriate perioperative management, correct implant selection, and accurate surgical technique. The consequences of performing a knee reconstruction inaccurately have been well documented for TKA, unicondylar arthroplasty, ACL reconstruction, and high tibial osteotomy.*

Although mechanical instrumentation has significantly increased the accuracy and reliability with which knee reconstructions are performed, errors in implant and limb alignment continue to occur, even when the procedures are performed by experienced surgeons. Moreover, the accuracy with which these procedures are performed is dependent on the knowledge and experience of the surgeon and the frequency with which the surgeon performs the procedure. CAS techniques have been developed to address the inherent limitations of mechanical instrumentation. The goals of integrating CAS with knee reconstruction techniques are to increase the accuracy of these procedures and reduce the proportion of alignment outliers that occur when these procedures are performed.

A surgeon can only use computer-assisted navigation safely and effectively if he or she is familiar with and comfortable with the procedure’s goals and the surgical techniques necessary to achieve those goals. Numerous reports have confirmed that when surgeons experienced in the manual performance of the knee reconstruction procedure use CAS techniques, average implant and limb alignment is improved and the incidence of outliers is reduced.^* Moreover, a recent study has indicated that when experienced surgeons and coworkers use techniques to perform knee reconstructive procedures, their ability to perform these procedures manually improves.¹⁴⁵

Errors can occur at numerous points during the performance of a knee reconstruction. Placement of the cutting blocks or ligament alignment jigs may be inaccurate. Attachment of these tools to bone may produce an error in their placement. The actual performance of the cut or drilling of the hole may be inaccurate (e.g., the saw blade may deflect). The final insertion of the implant may be inaccurate. Mechanical instrumentation does not provide a method for checking the accuracy of each of these steps of a knee reconstructive procedure. Another goal of integrating CAS with knee reconstruction is to provide the surgeon with a means to measure the accuracy with which each step of the procedure is performed.

Knee reconstructive procedures attempt to align limbs and implants correctly. They also seek to restore appropriate kinematic relationships and ligamentous stability to the knee.

Mechanical instrumentation cannot measure the precision with which knee kinematics and ligament stability are restored. CAS techniques make it possible to determine the presurgical kinematic relationships and ligamentous stability of the knee and help guide the surgeon to restore desired kinematic relationships and ligamentous balance.

Finally, CAS provides a unique and unprecedented opportunity to train residents and orthopedic surgeons to perform knee reconstruction procedures accurately.^95,^140,¹⁴⁸ CAS as a training tool has now been used more frequently. Applications have been developed and are now being used to allow surgeons to carry out self-assessment evaluation of their surgical skills for performing TKA and ACL surgery. Applications are also being developed to test the skills of surgeons and residents to learn various knee reconstruction procedures. Possibly, the most compelling rationale for applying CAS to knee reconstruction will prove to be the potential to revolutionize how surgeons develop and evaluate their surgical skills.