Electromagnetic navigation: TKA tool for accurate bone cuts, soft tissue balancing

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By Susan M. Rapp
ORTHOPAEDICS TODAY INTERNATIONAL 2007; 10:20
November 2007

Results of total knee arthroplasty performed using electromagnetic navigation systems have begun to show this technology�s potential as an intraoperative asset for joint replacement surgeons.

But before orthopaedic surgeons can fully embrace this type of navigation for regular use, the systems need to undergo more improvements and refinements, according to Mark A. Hartzband, MD.

Hartzband has used electromagnetic navigation in more than 100 total knee arthroplasty (TKA) cases over the past 2 years and analyzed its pros and cons.

�There are some distinct positives. It is fast and it is easy. There are no pins to bang into or get into your field. You don�t have to modify your exposure,� he said in a presentation at the 10th Annual Insall Scott Kelly Institute Sports Medicine and Total Knee & Hip Symposium in New York.

Hartzband noted some system improvements are underway in the form of new electromagnetic navigation instruments that are intuitive to use and easy to align inside small incisions. They may eliminate traditional instrumentation altogether.

With these developments on the horizon, he believes the popularity of electromagnetic navigation systems should increase, although system cost remains an issue.

�These are expensive systems and that has been what has limited [their] growth in this marketplace,� Hartzband said.

Hartzband discussed the differences between electromagnetic navigation and the more popular optical tracking systems. An electromagnetic system eliminates the need for special cameras, percutaneous pins and calibrating surgical instruments. �It is much easier to handle in terms of line of sight than an optical system,� he said

Hartzband uses electromagnetic navigation during TKA as a reference point for making bone cuts and soft tissue balancing. �I prefer to use it as a check rather than as a guide,� he said.

�It is a nice teaching tool as long as you don�t make it the only teacher in the room,� he said.

After completing dynamic reference frame placement, the system screen displays the tibial and femoral landmarks.

Once Dr. Hartzband makes the navigated cuts in the femur, he will navigate the tibial cuts. After placing the components, he relies on electromagnetic navigation to help complete soft tissue balancing and check kinematics.

Electromagnetic navigation systems work via an electromagnetic field generated by a hand-held emitter, which can be moved around the operating field. Instruments are equipped with a magnetic coil designed to work with the system. As each one is introduced it disrupts the electromagnetic field. The system�s computer, which has special tracking software, then recognizes the instrument and its three-dimensional location in the surgical field.

Before starting a navigated TKA procedure, the surgeon inserts two dime-sized dynamic reference frames (DRF) through small incisions made above and below the knee joint and fixes them with cortical screws.

The incisions are made in the anteromedial femur and inframedial tibia.

The surgeon then digitizes the center of the hip on-screen and uses that data and information from the DRFs as reference points for finding tibial and femoral surgical landmarks.

�I think landmarking is really the secret difficulty in all these navigated cases,� Hartzband said, adding that accurate landmarks are essential for a good outcome. They not only define the knee�s baseline kinematics before TKA, but improve the accuracy of subsequent femoral and tibial bone cuts.

Electromagnetic navigation also avoids the need to place optical pins, which can add up to 20 minutes to the surgery. �There is a morbidity to drilling extra pin sites. � You always have the ugly risk of a stress riser at a pin site and potential fracture,� Hartzband said.

�It is particularly advantageous for complex cases, the problem being you have to be good at the simple cases if you are going to bring it into a complex case,� he said.

The system�s extramedullary technique for navigating bone cuts is an advantage over ones that use intramedullary devices, since it does not push any of the patient�s fat into the system.

For more information:
Mark A. Hartzband, MD, can be reached at Hartzband Joint Replacement Institute, 10 Forest Ave., Paramus, NJ 07652, U.S.A.; +1-201-291-4040; e-mail: [email protected]. He has indicated he is a consultant to and receives research support and royalties from Zimmer Inc.
Reference:

Hartzband MA. Electromagnetic navigation in TKA. Presented at the 10th Annual Insall Scott Kelly Institute Sports Medicine and Total Knee & Hip Symposium. Sept. 14-16, 2007. New York.