Mechanical Alignment and Gap Balancing in Total Knee Arthroplasty: Rationale and Technique

The results of TKA are not uniformly successful. 20% of patients aren’t fully satisfied with their pain relief and function following TKA and up to 1/3^rdof patients have residual symptoms with activity. This leads to an increase in revision TKA. The primary etiologies for revision have evolved, but instability and malalignment are still common. Careful attention to meticulous surgical technique is critical to avoid revisions.

Measured Resection and Gap Balancing are two techniques for achieving the goals of TKA—coronal plane alignment, and coronal and sagittal plane balance. The primary difference between them is how femoral rotation is set.

With Measured Resection the amount of bone resected is equal to the thickness of the implants. Femoral rotation is predicated off of bony landmarks—transepicondylar, anteroposterior, and posterior condylar axes. Soft tissue balance is accomplished after the bony cuts are completed. The proponents of this approach underscore its ability to maintain the joint line.

With Gap Balancing the soft tissues are balanced first, and the bone resected around the soft tissues. Femoral rotation is determined by creating a symmetric flexion space within the balanced soft-tissue envelope. Classically, the balanced flexion space was created first, matching the extension space to it by adjusting the joint line. The modern hybrid approach utilizes a measured resection technique for the distal femur and proximal tibia, predicated off of the mechanical axes, and then balances the extension space with soft tissue releases when necessary. In flexion with the ligaments tensioned, femoral rotation is adjusted to create a rectangular flexion space, equal to the extension space. This approach has resulted in reliable and reproducible outcomes, minimizing joint line elevation while establishing stability and gap balance throughout motion. A recent meta-analysis suggested that “gap balancing techniques could provide better results than measured resection techniques in TKA.