Study finds improved component alignment from minimally invasive TKA involving computer navigation

Investigators found that, despite an increased operative time, computer-assisted TKA patients had significantly less blood loss.

Using computer-assisted navigation during minimally invasive total knee arthroplasty appears to improve postoperative radiographic prosthesis alignment compared to conventional knee replacement procedures, a prospective study found.

Patients treated with minimally invasive computer-assisted surgery also had increased functional recovery during the first month postop, the study authors noted.

Andrew Quoc Dutton, MBBS, FRCS, and colleagues in Singapore, investigated whether combining computer-assisted navigation with a minimally invasive total knee arthroplasty (TKA) technique would result in improved prosthetic alignment compared with conventional, non-navigated TKA. The study included 108 consecutive patients; 56 were randomly assigned to undergo conventional surgery and 52 were randomly assigned to undergo the minimally invasive approach.

In all cases, patients had substantial pain and loss of function due to knee osteoarthritis, any degree of genu varum deformity and 15° or less of genu valgum, according to the study, published in The Journal of Bone and Joint Surgery (Am).

"With the numbers available, no significant differences were noted between the two groups with respect to preoperative clinical data," including preoperative Oxford knee scores, Knee Society scores and degrees of deformity, the authors noted.

Both treatment groups received the same pre-emptive analgesic regimen, which was initiated 1 day before surgery, and the same standardized postoperative analgesic regimen. Also, the operating surgeon implanted an identical cemented posterior cruciate-retaining prosthesis with patellar resurfacing (PFC, DePuy, a Johnson & Johnson Company) in all cases, according to the study.

The researchers found that the minimally invasive, computer-assisted procedures required an additional 24 minutes on average to complete, significantly longer compared to the conventional TKA procedures.

However, "Despite the increased operative time, the amount of blood loss as reflected in the difference between the preoperative and postoperative hemoglobin levels was less for the computer-assisted minimally invasive [TKA] group," the authors noted.

Both groups had similar postoperative pain scores, which averaged less than 2 points on the Visual Analog Scale. But, patients in the minimally invasive TKA group showed significantly better function at 2 days postop.

The researchers found that 26 patients in the minimally invasive, computer-assisted TKA group could perform straight-leg raises, inner range quadriceps muscle contractions and knee flexion greater than 90° by 2 days after surgery vs. 17 patients in the conventional TKA group (P = .049).

"As a result, a higher number of patients in the computer-assisted, minimally invasive [TKA] group were discharged from the hospital at an earlier time," the authors wrote.

The duration of postoperative hospitalization averaged 3.3 days for the computer-assisted treatment group and 4.5 days for the conventional TKA group (P = .001), according to the study.

"At 1 month postoperatively, the number of patients who were able to walk independently for more than 30 minutes was greater in the computer-assisted, minimally invasive [TKA] group than in the conventional [TKA] group (P = .04)," the authors added. "However, the difference was not significant at 3 and 6 months," they noted.

Regarding radiographic alignment, significantly more patients treated with minimally invasive TKA had their implants within ±3° of neutral for the sagittal tibial component angle and for the coronal tibiofemoral angle.

There were no significant differences between the two treatment groups regarding alignment for the coronal femoral component angles, coronal tibial component angles and sagittal femoral component angles, according to the study.

For more information:
Dutton AQ, Yeo SJ, Yang KY, et al. Computer-assisted minimally invasive total knee arthroplasty compared with standard total knee arthroplasty. A prospective, randomized study. J Bone Joint Surg Am. 2008;90-A:2-9.