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CT-based navigation system determines balance point for knee ligaments during TKA

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Japanese researchers have found through the use of a CT-based navigation system that balancing of the ligaments during total knee arthroplasty is accomplished at 0° and 90°. The findings were presented by Takafumi Hiranaka at the British Orthopaedic Association and the Irish Orthopaedic Association Combined Meeting 2011, in Dublin.

“The purpose of this study is to evaluate the ligament balancing at various knee angles using a CT-based navigation system,” Hiranaka said.

Acknowledging that ligament balance is critical in total knee arthroplasty (TKA), Hiranaka noted leg alignment is also fundamental — and while balancing is adjusted at 0° to 90° of knee flexion, the importance of other angles is never considered. He and his research team used computer navigation during TKA for facilitating precise bone cutting and in situ evaluation of kinematics.

The study itself involved 22 patients who underwent TKA with the use of a CT-based navigation system. Varus and valgus stresse were applied manually following implantation, with ligament balance being evaluated.

“Through the use of the navigation computer, the balance angle (BA) can be defined as the angle between the tibia and femur cutting plane under the valgus stress subtracted by that under the varus angle,” the authors wrote in the study. They went on to note that a positive BA implies a medial side that is looser than the lateral side.

The reported mean BA of knee flexion positions at 0°, 30°, 60°, 90° and 120° were -1.5°, -4.8°, 5.1°, -0.9° and -9.5°, respectively.

“Although the balancing was good at 0° and 90°, the lateral plane is loose at 30° and 120° and the medial side is loose at 60°,” Hiranaka concluded. “The acceptable range of imbalance is unknown, and so more research is needed.”

Reference:

• Hiranaka T, Hida Y, Uemoto H, et al. An evaluation of ligament balancing of total knee arthroplasty in various flexion angles using a CT-based navigation system. Presented at the British Orthopaedic Association and the Irish Orthopaedic Association Combined Meeting 2011. Sept. 13-16. Dublin.

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