February 01, 2012
4 min read

CAOS: The direction and future of robotics and navigation explored

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Anthony M. DiGioia III
Anthony M. DiGioia III, Editor
S. David Stulberg
S. David Stulberg

It has been almost 15 years since the first image-free navigated total knee replacement (TKR) was performed in Grenoble, France. The procedure represented the culmination of years of basic investigations carried out around the world necessary for the performance of computer-assisted orthopedic surgery (CAOS) and ushered in an era of vigorous development, application and evaluation of this technology. The purpose of this article is to summarize the impact that CAOS has had on the way we carry out our surgical procedures, consider what we have learned from applying this technology and to describe current and probable future developments in this field.

CAOS embodies a broad spectrum of preoperative imaging technologies and intraoperative surgical tools and measuring devices that couple preoperative planning with surgical execution. In principal, a precise patient-specific preoperative plan can be generated and accurately applied in the operating room using computer-assisted surgical tools. The underlying principle of CAOS is that the more accurately performed the operation, the better the clinical outcome.

Consistent findings

Although computer-based technologies are being applied in a variety of orthopedic specialties, the most interest and activity has been in the field of adult knee and hip reconstruction. Numerous publications reflect this interest. Meta-analyses have been carried out and provide generally consistent observations with regard to the impact of using CAOS in total knee arthroplasty (TKA) surgery:

  1. The incidence of limb mechanical alignment outliers of greater than 3· is substantially reduced when navigation, rather than conventional techniques, is used;
  2. The risk of greater than 3° misalignment for frontal plane femoral and tibial component alignment is less with navigation than conventional techniques;
  3. Surgical time is greater when CAOS techniques are used; and
  4. There is no evidence, at this time, that these improvements in limb and implant alignment result in improved clinical outcomes or prolonged arthroplasty longevity.

Although the need for accurate implant positioning, especially acetabular component alignment, is considered critical to the successful outcome of a total hip arthroplasty (THA) and though numerous reports have pointed out that accurate and consistent implant positioning is difficult to achieve with conventional total hip instrumentation, the use of navigation in THA has been applied less frequently than in TKA. Nevertheless, a review of the articles published on the use of CAOS in THA has found that cup positioning is more consistent when navigation is used. This reduction in outliers has not yet been shown to result in improved clinical outcomes or improved hip stability. Although the use of navigation in THA can also allow measured restoration of leg length, joint offset and version, there is, as yet, no consistent evidence that this potential benefit can be more consistently achieved with CAOS than with conventional instruments. As is true when navigation is used in TKA, the operative times are increased when computer-assisted techniques are used in THA.

In spite of the enormous amount of work devoted to this field and the intense interest the technology has generated, its use in the daily practice of orthopedic surgery has remained extremely limited. CAOS techniques are currently used in less than 5% of total hip and knee procedures. There are a number of reasons for this failure of navigation to be widely adopted:

  1. The computer-assisted tools that have been available in the past 15 years are expensive and cumbersome;
  2. They frequently introduce surgical steps that are not a routine part of the orthopedic procedure, making the procedures more challenging for surgeons and their operating room staffs;
  3. The use of the tools is associated with increased operative time;
  4. The alignment goals often sought by the hip and knee navigation programs have been called into question. It has been suggested, for example, that re-establishing a mechanical axis of zero in all patients undergoing TKR surgery may be inappropriate and that factors, in addition to limb and implant alignment, may have an important impact on the surgical results; and
  5. There is virtually no evidence that the use of CAOS techniques leads to improved clinical outcomes.

Future requirements

Discuss in OrthoMind
Discuss in OrthoMind

However, there remains a strong interest in improving the accuracy and reliability of orthopedic procedures. There exists an ongoing willingness on the part of the orthopedic community to consider technologies that will lead to increased surgical accuracy and reliability. The experience with what might be characterized as first generation CAOS technologies has helped define the requirements for future computer-assisted surgery developments. These requirements are that the technology be accurate and safe, associated with a relatively short learning curve, adaptable to familiar instrumentation, easy for surgeons and staff to use, and efficient.

In particular, the cost of the technology must be clinically justifiable. Surgeons and hospitals are likely to be incentivized to consider computer-based surgical technologies if the costs offset the cost of current non-CAOS technologies. For example, does the computer-based technology improve operating room efficiency or reduce the need for instruments or implant inventories.

A number of new CAOS technologies, some based upon the principles and techniques of navigation, are being introduced and evaluated. A new generation of robots to prepare for the insertion of knee and hip implants is being introduced. Unlike earlier robots, current systems act like constraining devices and provide for substantial surgeon control. Customized instrumentation based upon preoperative plans derived from computer reconstructions of MRIs or CT scans is being used to insert total knee implants. Custom-made implants and supporting customized instrumentation for total knee implants are also being evaluated.

As the cost of the computer-based imaging technology and rapid processing manufacturing technologies decrease, the use of custom-made instrumentation is likely to increase. The procedures are accurate, have a short learning curve, are adaptable to familiar instrumentation and are efficient. The tools are easy for surgeons and staff to use. Computer-based intraoperative sensors are also being used to measure soft tissue balancing in total knee surgery. The use of so-called “smart tools” (i.e., tools that indicate the accuracy with which a task is performed) is likely to increase significantly in the next few years. Moreover, “smart implants” (e.g., tibial components with pressure sensors) will soon be available for evaluation. The acceptance of all of these CAOS technologies will depend upon the extent to which they satisfy the aforementioned requirements. In particular, the cost of the technology must be clinically justifiable.

Finally, CAOS has had a substantial impact on the way surgery is taught. Simulation laboratories for arthroscopic procedures have been developed. Computer-based interactive preoperative planning tools are available. The impact of computer-based technologies on the way in which surgery is taught and evaluated is just beginning to be felt.

  • Mason JB, Fehring TK, Estok R, et al. Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery. J Arthroplasty. 2007;22(8):1097-1106.
  • Ulrich SD, Bonutti PM, Seyler TM, et al. Outcomes-based evaluations supporting computer-assisted surgery and minimally invasive surgery for total hip arthroplasty. Expert Rev Med Devices. 2007;4(6):873-883.
  • S. David Stulberg, MD, can be reached at Northwestern University Feinberg School of Medicine, 680 N. Lake Shore Dr., #1068, Chicago, IL 60611; 312-664-6848; email: jointsurg@northwestern.edu.
  • Disclosures: Stulberg has relevant financial disclosures with Aesculap, Blue Belt Technologies, Innomed, Stryker and Zimmer.