Issue: Issue 5 2006
September 01, 2006
7 min read

Computer guidance for TJR: What comprises state-of-the-art care?

Top surgeons discuss the current status of computer-assisted orthopaedic surgery (CAOS) tools for joint replacement.

Issue: Issue 5 2006
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William J. Robb, MD  [photo]William J. Robb, MD
Chairman, Department of Orthopaedic Surgery, Evanston Northwestern Healthcare, Illinois Bone and Joint Institute, Glenview, U.S.A

Lawrence D. Dorr, MD  [photo]Lawrence D. Dorr, MD
Medical Director, Arthritis Institute, Inglewoog and Los Angeles, U.S.A.

Jean-Yves Jenny, MD  [photo]Jean-Yves Jenny, MD
Treasurer, International Society for Computer-Assisted Orthopaedic Surgery; Director, Traumatology Center, Illkrich, France

William Hozack, MD  [photo]William Hozack, MD
Director, Joint Replacement Service, Thomas Jefferson University Hospital; Director of Clinical Research, Rothman Institute, Philadelphia, U.S.A.

S. David Stulberg, MD  [photo]S. David Stulberg, MD
Professor, Northwestern University School of Medicine; Orthopaedic Surgeon, Northwestern Memorial Hospital, Chicago, U.S.A.

Many surgeons may be familiar with reports of improved limb alignment and component alignment, better cutting accuracy, enhanced 3-D understanding and other advantages offered by computer-guided systems. But when will this promising technology become the gold standard?

To find out, Orthopaedics Today asked joint reconstruction specialist William J. Robb, MD, to interview some experts in this field to share their expertise.

In a variation on Orthopaedics Today’s typical Round Table, our moderator questions panelists individually in their areas of expertise.

William J. Robb, MD (Moderator): Do you use CAOS routinely for total hip and knee replacement?

Lawrence D. Dorr, MD: I am using CAOS only for total hip replacement (THR) at this time. For nearly three years, I worked with Orthosoft on an imageless program for hip replacement that is practical for surgeons and not oriented to engineers. We essentially started from scratch, so I had to spend several months just defining the requirements for the tracking devices and the tools so that we could get reproducible results.

We also had to define the registration technique because we operate with the patient in the lateral position, and the AP plane of the pelvis needs to be registered, which we found could not be done reproducibly with the patient in the lateral position. We detailed these experiences in an article published in the Iowa Orthopaedic Journal [June 2005; 25:1-9].

At this time, we have an accurate and reproducible program for the acetabulum. We are also working on a program that will include the femur and allow the biomechanical reconstruction of the hip to be as accurate and reproducible as the implantation of the acetabular component.

Robb: What currently is the greatest limitation of CAOS for THR?

Dorr: One of the greatest limits of computer navigation for THR is that engineers have designed the software for many of these programs without proper advice from surgeons. Therefore, the software is not entirely surgeon-friendly, which results in more time needed in the operating room to accomplish goals, as well as added confusion regarding the numbers generated for the acetabular positioning.

Some people believe that the best information the computer can provide for the acetabulum is inclination and anteversion, but in fact, for proper implantation and placement of the acetabulum, it is critical for the surgeon to know the center of rotation of the cup compared to the center of rotation of the native acetabulum.

The surgeon also needs to know the amount of coverage of the cup, the amount of medialization of the cup and the inclination of the cup, which helps achieve the proper coverage.

Robb: What technology breakthrough is needed to make CAOS the “gold standard” for total hip replacement?

Dorr: I think the next technology advance that will make CAOS friendlier for the surgeon is changing the tracking to electromagnetic, radiofrequency or ultrasound (or a combination) formats.

One of the biggest benefits for patients is that computer navigation can “level the playing field” between expert and average surgeons. The best total hip replacement surgeons — usually the most experienced ones — have a better three-dimensional understanding of component placements and mating components than the majority of their colleagues. Fortunately, the computer can provide real-time knowledge of the component positions for most surgeons, which replaces the need for that three-dimensional understanding. This allows these surgeons to create a total hip replacement that is just as accurately placed as those placed by the most experienced surgeon.

Robb: What benefits have your patients realized by your using computer-assisted techniques in total knee replacement (TKR)?

Jean-Yves Jenny, MD: Several scientific studies have shown that patients operated on for a TKR with the help of a navigation system benefit from more accurate bone resections, regardless of what system is used. When accuracy of implantation is measured on postoperative X-rays, it is generally accepted that there are fewer outliers (ie, patients with an excessive varus or valgus). This malposition is recognized as a factor of earlier failure, mainly because of polyethylene wear. Therefore, patients operated on with computer assistance might expect better long-term outcomes and fewer revisions. In our experience with the newer software versions, computer assistance also allows accurate measurements of the ligamentous balance of the knee, both before and after implantation.

Robb: How much longer does the procedure take when using a computer-navigated approach, and will it eventually become the standard of care for TKR?

Jenny: The additional operative time for computer-assisted total knee replacement in comparison to the conventional technique is about 10 minutes. This additional operative time is longer at the beginning of the surgeon’s experience, but it decreases quickly when the surgen and his staff gain more experience. We think the additional time is fully compensated by the addtional information we gather from the procedure (such as more accurate bone resections).

Robb: What type of learning curve should a new user expect to deal with in using computer-assisted guidance for TKR?

Jenny: We specifically studied the learning curve of computer-assisted TKR, and our paper is being prepared and will be submitted to the British edition of the Journal of Bone and Joint Surgery. We studied the accuracy of implantation of a navigated TKR in experienced and beginning centers. Our results showed that: early radiological results were not different among beginning and experienced centers; there was a significant learning curve for the additional operative time, with a mean increase of 10 minutes in beginning centers compared to experienced centers; and surgeons learning how to use CAOS required the same additional operative time as that needed by experienced surgeons after 30 navigated implantations. We concluded that there was no learning curve regarding the accuracy of implantation at the expense of an additional operative time of about 10 minutes during the first 30 procedures.

Robb: What advise do you have for surgeons considering getting started using CAOS in their practice?

Jenny: Surgeons who are considering getting started using CAOS should carefully choose the CAOS system they want to use after performing cadaver or saw-bone tests, and then visit an orthopaedic surgeon who is experienced using it.

Next, they should accept the fact that they will spend more time in the operating room performing the procedures for the first 30 cases. They should also carefully document and compare the navigated cases vs. the conventional ones to control their quality of care and be convinced that CAOS brings relevant advantages to conventional approaches.

I am convinced that computer-assisted techniques will become the standard of care for total knee arthroplasty (TKA). Older surgeons are used to conventional techniques, and most of them prefer to keep using them, but residents who are actually learning TKA with computer assistance from the very beginning are mostly enthusiastic and do not want to go back to conventional techniques.

Robb: Dr. Stulberg, in your opinion, what do you feel is a normal learning curve for CAOS for total hip and knee replacement for the average total joint surgeon? Has the learning curve changed in the past two years?

S. David Stulberg, MD: In order to use CAOS successfully for THA and TKA, a surgeon must first be familiar with and comfortable with his or her technique for performing these procedures. CAOS will only be helpful if a surgeon has a clear idea of what he or she wishes to accomplish.

The time required to integrate CAOS into a surgeon’s usual TKA technique has decreased substantially in the last two years. The CAOS TKA techniques have become more user-friendly, less cumbersome and more intuitive. But the CAOS-THA techniques are, in my opinion, still developing.

Robb: Based upon your experience – are there contraindications to CAOS for primary total hip or knee replacement?

Stulberg: Once a surgeon has mastered the CAOS technique, he or she can apply it to most primary arthroplasty procedures. However, current CAOS TKA techniques cannot be used if a patient has a fused hip (ie, the registration of the center of the femoral head cannot be performed) or a nonspherical femoral head. CAOS may also be inappropriate in patients with significant arthritis of the hip, for registration may result in pelvic movement and an inaccurate determination of the center of the femoral head.

Patients with significant hip joint deformity are also not candidates for CAOS TKA, and the procedure is possible but more difficult in patients with large thighs. Secure rigid fixation of the bicortical screws or pins is difficult to achieve. Movement of the pins during the procedure is more likely, and achieving accurate “line of sight” may be difficult.

CAOS should be done with particular care in patients with osteoporosis to avoid femoral or tibial fractures. Patients with severe femoral-tibial subluxation, ankylosis or intra-articular deformity may be candidates for CAOS, but registration must be done carefully and thoughtfully.

Robb: What is the most important added value of CAOS for total hip and knee replacement?

Stulberg: The most important added value of CAOS is that it allows the accuracy of each step of the procedure to be measured. The surgeon can determine if the cutting block placement is accurate, can determine if the resection is accurate and can determine if the implant placement is accurate. Surgeons who learn what accurate alignment of implant and limb is using CAOS develop much better judgment about what constitutes correct limb and implant orientation.

Robb: Have you seen any complication that resulted directly from CAOS in total hip and knee replacement patients?

William Hozack, MD: Complications related to CAOS could come directly from the newer instrumentation or indirectly from improper use of the instrumentation. Examples of the direct complications include fracture of the bone related to the screws implanted to fixate the registration arrays, infection from pins or screws placed outside the incision used to implant the hip or knee replacement, infection related to increased surgical time, and direct neurovascular injury related to the placement of the registration arrays. I have seen none of these. The only publication I have seen documenting complications was by Sikorski.

Complications related to improper use of the instrumentation could lead to malaligned components, malrotated component, dislocation or leg length discrepancy. As with any instrumentation system, it is the surgeon who determines how well it works.

Robb: Have you found that there are any unexpected benefits of CAOS in THA and TKA?

Hozack: CAOS improves my surgical skills. It provides me with real-time feedback and accurate information during surgery. I have an improved three-dimensional understanding of acetabular anatomy and acetabular component positioning.

CAOS has also helped me understand how well I use a saw to make bone cuts, enabling me to modify my technique to improve the accuracy of my initial cut.

CAOS actually reduces the amount of instrumentation necessary to perform TKA. Once I fully incorporated the CAOS instrumentation, I was able to simplify my sets and reduce the time needed to set up the case.

Also, CAOS has been invaluable in teaching my residents and fellows total knee arthroplasty surgery.

Finally, soft tissue balancing is the least well-calibrated technique in TKA, and only computer-assisted information will allow the surgeon to understand this critical phase of the operation and to make informed decisions.