Summary

Balancing a TKA only by bone recuts is reliable and reproducible with a robotic arm under the control of a load sensor with NO soft tissue release, it improves clinical results at one year follow up

Abstract

Achieving a well balanced total knee arthroplasty (TKA) throughout the entire range of motion leads to improved patient outcomes and satisfaction. Sensor-assisted technology allows the surgeon to quantitatively assess and address imbalance through either soft tissue releases or bone recuts. However soft tissue releases lead to unpredictable gap increments and over-releases.
The primary objective of this study was to demonstrate the ability to achieve a quantitatively well balanced knee arthroplasty by combining a robotic arm (MAKO, Stryker, Kalamazoo, Michigan, USA) and an intra-operative load sensor (Verasense, Stryker, Kalamazoo, Michigan, USA ), while avoiding any soft tissue correction.
During a consecutive and prospective serie of 56 robotic arm total knee arthroplasties, intra-operative load sensors, were used following the initial bone resections to quantitatively assess the knee’s state of balance through the range of motion with trial components in place. Load measurements were taken at 10 and 90 degrees of knee flexion. A balanced knee was defined as a force between the femur and the tibia between 22 and 200 Newton, with a difference between the lateral and medial side less than 66 Newton. Depending on these parameters, the thickness of the polyethylene insert and/or a bone recut(s) is made. The bone recuts are made with the interface of the robotic arm in the three planes of space, half-millimeter by half-millimeter with between each new recut a control by the load sensor. The initial load numbers were recorded as well as the numbers and type of subsequent corrections needed to achieve a quantitative well balanced TKA.
Of the 56 robotics cases, only 23 (41%) were well-balanced after the initial bone cuts (restricted kinematic alignment adjusted after tensioning collateral ligaments during surgery). In 29 cases, one or two, and rarely three bone recut(s) were required to balance the knee. It should be explicitly noted that no soft tissue release were done for any of the 56 cases. The posterior cruciate ligament was always kept intact. At the end of the procedure 50 cases (89%) were well balanced in extension, 50 (89%) in flexion and 43 (76%) in flexion and in extension. Recuts improved Flexion/Extension unbalanced knee in 95% of cases. At one year follow up the fonctionnal IKSS score was 76,9 (+/-16) and the Forgotten Joint Score 69,3 (+/-28). According the FJS12-PASS and an ordinal logistic regression an unbalanced knee at 10° or 90° of flexion is associated with a bad clinical result.
Based on this study, a well soft-tissue balanced TKA matters (imbalance TKA leads to poor clinical results) and balancing a TKA only by bone recuts is reliable and reproducible with a robotic arm under the control of a load sensor with NO soft tissue release. It works better if recut is only on tibial side (changing in femoral rotation is still an issue). Robotic arm and load sensors will help us to collect more data and define the right boundaries of a well balanced and aligned TKA.