More work needed to perfect imageless navigations for UKR

urgeons skilled in using one system found it improved postop alignment but lengthened the OR time.

Issue: June 2005

Using computed tomography-free navigation systems to implant unicompartmental knee components is still an inefficient way to do these operations and it could be some time before this technique truly becomes a surgical asset, according to investigators who prospectively studied use of one system.

In their recent study, the investigators found that the system helped make the surgery more accurate, but it consistently took them about 15 minutes longer to complete it than when doing a standard unicompartmental knee replacement (UKR). Some aspects of the two types of surgeries, however, were about the same, including the amount of intraoperative blood loss and the patients’ postoperative range of motion and pain, said Lars Perlick, MD.

“The navigational system enhances the quality and you have an improvement in component and leg alignments, but you need additional operation time,” he said.

Pluses and minuses

Perlick and his co-authors have used the navigation system they studied in nearly 700 total knee surgeries and about 70 UKR procedures. For this study, they prospectively performed UKA in 40 patients; they used the standard techniques on 20 patients and navigation techniques on the other 20 patients. Despite their skill, using the high-tech system for UKR always took longer than the standard technique.

They theorized that the limited view the surgeon has during a minimally invasive UKR might also increase any problems stemming from using a navigational system in these cases. Perlick presented results of the study at the American Academy of Orthopaedic Surgeons 72nd Annual Meeting.

Accurate valgus

The researchers said they thought one advantage of the system was its ability to attain fairly accurate varus alignment, particularly when they sought to place components within 2° of what the system indicated was proper based on a 0° to 4° window of accuracy.

“We found less outliers in the navigation group — only one, which was a cementing error — compared with the conventional technique,” he said. That meant 95% of navigation-operated patients had an in-range mechanical axis compared to 70% in the other group.

Based on postoperative radiographs, results using the navigation system correlated to what the surgeons saw on the OR monitor during surgery. “What you see is what you get,” Perlick said.

Regarding tibial and femoral component alignment, “we found quite a good adjustment for the tibial component, even with the conventional technique, but a huge standard deviation for the femoral component for flexion and extension, which might be explained by the small window when using the tourniquet and other drapes.”

Although investigators thought the system they reported on improved upon earlier designs, Perlick recommended further modifications to improve its accuracy. He also suggested that the femoral cutting plan be changeable, so that if the surgeon was dissatisfied with the bone-cutting plan that the system supplies, he or she gets can rework it.

“It’s quite difficult if you have a misalignment to correct it afterwards, so you have to be very precise,” he said, adding that more information is needed about the limits of the component and leg alignment.

For more information:

Perlick L, Baethis H, Luering C, Grifka J. Minimally invasive unicompartmental knee replacement with a non-image-based navigation system. #74. Presented at the American Academy of Orthopaedic Surgeons 72nd Annual Meeting. Feb. 23-27, 2005. Washington.