Selecting the right navigation tool for knee arthroplasty

Excellent position tracking is vital to a successful navigation procedure.

Issue: Issue 6 2004

French flag ATHENS — Computer-assisted navigation tools can make a difference in an orthopaedic surgeon’s ability to perform a total knee arthroplasty quickly and safely, but knowing how and when to use the tools is half the battle, said a French surgeon.

Not surprisingly, the current “passive” navigation tools (ie, non-robotic) are designed to help orthopaedic surgeons see parts of the knee that are often hidden from view during a knee arthroplasty, including the center of the femoral head, the femoral mechanical axis and the angle of the femur. “We also have trouble seeing the tibial mechanical axis, the femoral-tibial axis, the femoral rotation and the reducibility of the deformity,” said D. Saragaglia, MD, of Grenoble, France, who discussed the topic in a special symposium at the 11th ESSKA Congress. ESSKA 2004 [icon]

He compared using navigation in the operating room to using navigation instruments to pilot a ship.

“When you’re far out to sea and away from landmarks, it’s easy to get lost. That’s when a navigation device for the ship is necessary, but it’s not [vital] to have navigation when you’re near the coast and you can see everything,” he said.

“The same thing goes for knee surgery. It’s important to see things that you can’t with the [naked] eye, but I think it’s useless to rely on the computer screen if you can already see what you need to. It’s also very important not to complicate the technique and increase the cost of the artificial knee implantation.”

Computed tomography

Saragaglia noted the difference between computed tomography (CT)-based and CT-free navigation systems.

“If you use CT-based navigation, you can get 3-D reconstruction of the knee on the screen,” he said. However, “You have to prepare and register the patient prior to using the navigation system. This can take 30 minutes for an experienced surgeon and longer for someone not as experienced.” This registration process involves the matching of preoperative CT images or planning information to the knee of the patient on the operating table.

Nearly all CT-free systems are accurate at measuring access and gaps and do not require extensive preoperative CT or planning, he said. Instead, the surgeon places markers on the articulating bones, and by moving the joint, he can obtain the center of motion. The knee, hip and ankle motion centers reveal the functional axes of the femur and tibia.

However, even these systems have a few disadvantages. With the kinematic model, “You can have trouble reconstructing the knee on screen, and you have a problem if you use it for the stiff knee.”

With the bone morphing system, “The advantage is the possibility to reconstruct on the screen the knee via a 3-D reconstruction. However, you need to have a large exposure of the joint in order to screen all of the knee, including the tibial plateau and the condyles,” he said. “I also don’t know if the [device’s] library is very exhaustive and corresponds to all types of knees.”

When using a fluoroscopy-based system, there may be an increased risk of radiation exposure to the patient, surgeon and nurses during the operation, he said. “There is also the issue of the increased clutter in the operating room. You also need room to mobilize the fluoroscope, and there may be a problem with asepsis.”

Promising results

Since 1997, Saragaglia has used navigation systems in more than 600 mediated knee surgeries, including 450 total knee replacements, 130 osteotomies and 49 ACL reconstructions. Excellent position tracking, he acknowledged, is a key ingredient to a successful navigation procedure.

“Our results showed that we had 100% of our cases comprise between 177º and 183º of femorotibial angle” postoperatively, he said. “We found that this was more accurate than the conventional TKA technique [without navigation].”

Ongoing follow-up is necessary to determine if the survival rates for implants improve significantly when the surgeon used navigation.

“We don’t know that yet because we don’t have a very long follow-up yet [with navigation-based TKA procedures]. Also, we need to see if the rate of revision is less than without navigation,” he said.

For more information:

Saragaglia D. Navigation in total knee replacement. Presented at the 11th ESSKA Congress and 4th World Congress on Sports Trauma. May 5-8, 2004. Athens.