No difference in outcomes seen at 1 year follow-up when using navigation for TKA

Investigators found average surgical time increased 12 minutes for navigated TKAs.

LAS VEGAS — The improvements in prosthesis alignment and knee function typically touted as reasons to use computer navigation during total knee arthroplasty were not seen in a recent single-center randomized trial where Canadian investigators compared results in these cases to those done with traditional surgical techniques.

“Navigated knees did demonstrate a slight degree of increased varus relative to the non-navigated knees. We do not feel that this difference is actually clinically significant,” Thomas R. Turgeon, MD, MPH, FRCSC, said at the American Academy of Orthopaedic Surgeons annual meeting.

Surgical time was longer in the navigation group by 12 minutes on average, he said.

Similar groups

For the double-blinded study, three surgeons performed 145 total knee arthroplasty (TKA) procedures in 123 patients, using the Stryker navigation system for the 74 knees randomized to the navigation group. All patients received a Duracon PS prosthesis (Stryker) and underwent patellar resurfacing and standard protocols for surgical technique, anesthesia and postoperative care.

The groups were demographically similar, as were their preoperative WOMAC and SF-36 scale scores, which were also used as outcome measures.

Thomas R. Turgeon

All patients had full-length standing radiographs taken postoperatively. The first 15 patients in both groups also had knee CT scans prior to leaving the hospital.

Alignment issues

Investigators assessed the patients’ range of motion preoperatively. At 1-year postop both groups’ mean flexion was 115·.

The few differences between the groups had to do with alignment, according to Turgeon, who noted that increased varus alignment in the navigation group mainly related to differences in tibial alignment in the AP plane.

“Also of note, the tibial component on the lateral view had about 2· to 2.5· of increased posterior slope in the non-navigation group,” he said.

Outliers analyzed

Investigators found a slightly reduced standard deviation for mechanical axis and tibial slope in the navigated group compared to the non-navigated group.

The number of mechanical axis outliers, who were defined as those with knee alignment more than ± 3· from neutral, was nearly the same in both groups.

However, the rotational alignment of the femoral and tibial components in both groups tended toward internal rotation, Turgeon said.

This patient’s knee is representative of those randomized to undergo standard or computer-navigated TKA surgery in a study designed to identify differences between the techniques.

Full-length standing radiographs were taken postoperatively in all cases and some patients had knee CT scans. Investigators found few differences in the groups’ results at 1 year postop. Images: Turgeon TR

Good ROM

The navigated group’s SF-36 general health scores were better than in the traditionally operated group, but none of the functional outcomes differed at 1 year postoperative. Range of motion and total arc of motion were also similar, according to the results.

Turgeon was unsure what caused the navigated group’s slight increase in varus alignment. He speculated it may be due to landmarking issues at the surgery’s start or slightly internally rotating the tibial cut in conjunction with implanting the tibial base plate with added slope.

One attendee, who was trying to determine why Turgeon’s results were so different than the published randomized trials of computer-assisted TKA that show differences among the outliers, asked about the surgeons’ skill level.

All the investigators completed 20 navigated knees, minimum, with this system; two had done many more cases than that, Turgeon replied.

“Further long-term follow-up studies will be required to assess the impact of surgical navigation on knee implant survival,” he told Orthopedics Today.

For more information:

• Thomas R. Turgeon, MD, MPH, FRCSC, can be reached at Concordia Hip and Knee Institute, Ste. 300, 1155 Concordia Ave., Winnipeg, MB R2K 2M9 Canada; 204-926-1230; e-mail: tturgeon@concordiahospital.mb.ca. He receives research or institutional support from DePuy, a Johnson & Johnson company, Smith & Nephew and Zimmer.

Reference:

• Turgeon TR, Hiscox C, Bohm ER, et al. Randomized trial of computer assisted knee replacement: Impact on clinical and radiographic outcomes. Paper #253. Presented at the American Academy of Orthopaedic Surgeons 76th Annual Meeting. Feb. 25-28, 2009. Las Vegas.