Background: The Orthopilot TKA navigation system offers soft wear for optimizing soft tissue balance using gap technique. However there has been no study about reliability of navigation guided gap technique. The goal of present study was to establish the reliability of navigation guided gap technique.

Methods: The authors measured flexion and extension gap in medial and lateral side of knee joint after bone resection to evaluate the reliability of navigation guided soft tissue balancing. Between May 2004 and June 2006, gap data of 100 cases of navigation-guided total knee arthroplasty were analyzed. We defined trapezoidal gap (unsatisfactory soft tissue balancing) as a gap difference greater than 3 mm between medial and lateral side in extension, and 5 mm difference in 90 degree flexion. And gap difference between flexion and extension gap greater than 3 mm in the medial side, and 5 mm in the lateral side was also considered as a trapezoidal gap. Hospital for Special Surgery (HSS) scores and the range of motion (ROM) at latest follow-up were used for the clinical outcome assessment. The mechanical alignment of the limb was checked on a standing radiograph of the whole lower extremity obtained at the latest follow-up.

Results: Among 100 cases, 84 cases (84%) showed rectangular (acceptable) gap, but 16 cases (16%) were trapezoidal gap. At the latest follow up, mean range of motion (ROM) was 123.1° (range, 80°–150°) in the rectangular group and 120.3° (range, 85°–150°) in the trapezoidal group(p = 0.528). Neither improvement of ROM and HSS score nor correction of coronal alignment was found to be significantly different between the two groups.

Conclusions: This study suggests that navigation guided gap technique is a reliable method for optimizing soft tissue balance.

Level of Evidence: Therapeutic level IV