Computer-assisted TKA does not improve alignment - Academy News at the 2007 AAOS Annual Meeting

Computer-assisted TKA does not improve component alignment, orientation

By Carolyn Rogers

Does the use computer-assisted navigated total knee arthroplasty (TKA) lead to increased accuracy of component positioning when compared to conventional TKA?

No, reported the authors of scientific paper 498, “Alignment and orientation of the total knee components with and without navigation support.” In their study, the researchers found that “postoperative limb alignment was not significantly better in the computer-assisted group than in the conventional group.”

Bilateral comparison

Their conclusion is based on a prospective, randomized study of 100 patients who underwent bilateral simultaneous TKA. A computerized CT-free navigation system was used on one side and a conventional technique was used on the contralateral side. The order of usage of the navigation system and the conventional technique was assigned alternately to each side; when the navigation system was used first on the left knee in one patient, the conventional technique was used first on the left knee of the next patient.

The researchers found no significant differences in knee alignment, position of the femoral and tibial componenets, patellar angles, tibial surface capping or preoperative and postoperative joint lines between the two groups. There was no statistical difference in pain scores, range of motion scores, postoperative knee scores or function scores between the two knees.

The patients’ average age was 67.6 years (range, 54 to 83 years). Eighty-five patients were women and 15 were men. All 100 patients had been diagnosed with osteoarthritis, and none had undergone a previous operation.

Clinical and radiographic evaluations were done preoperatively, at three months and one year after the operation and yearly thereafter. The prevalence of outliers between computer-assisted and conventional groups was also examined. Postoperative computer tomographies, using a multi-slice scanner, were performed to determine the rotational alignment of femoral and tibial components. The mean follow-up was 2.6 years (range, two to three years).

“Operating and tourniquet times were significantly (P<0.001) longer in the navigation group,” the authors reported. However, length of incision, intraoperative blood loss, hemovac drainage, duration of hemovac and amount of transfusion were not significantly different (P>0.05) between the two groups.

Total knee score (90 vs. 89 points), pain score (40 points in each group), and range of motion (127 vs. 126) were not found to be statistically different (P>0.05) between the two groups.

Computer-assisted navigation

Proper component alignment is essential for determining the outcomes of TKA. Incorrect alignment can lead to abnormal wear, premature mechanical lossening of the components and patellofemoral problems.

“Computer-assisted navigation systems have been developed to improve the accuracy of alignment and orientation of the components in TKA,” the researchers noted. “The expectation is that [the use of] such systems will result in TKAs that are better aligned, with the benefits of better functioning and improved longevity.”

In their study, researchers found postoperative limb alignment (tibio-femoral angle) exceeded 3 of varus/valgus deviation in 18 percent the conventional TKAs and in 21 percent of the computer-assisted TKAs. They acknowledged, however, that “utilization of the computer-assisted navigated TKA contributed to improve the surgical technique performing the conventional TKA,” leading to a reduction in the prevalence of outliers in the conventional group.

Researchers also noted the difficulty in obtaining accurate registration, which resulted in anterior femoral notching in six knees in the computer-assisted group. They recommended that “registration of the anterior femoral cortex should be confined to just proximal to the distal femoral articular surface to avoid anterior notching of the distal femur.”

The researchers acknowledged the difficulty in determining a function scores for patients who had bilateral TKA, noting that one knee invariably affects the other during daily activity and that patients cannot distinguish how far they can walk on their conventional knee versus their navigation knee. However, the researchers believe they were able to obtain fairly accurate information after careful assessment of the performance of each knee.

The research team includes Young-Hoo Kim, MD; Sung-Hwan Yoon, MD, and Jun-Shik Kim, MD—all of Seoul, Republic of Korea. The authors report no conflicts of interest.

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