Achieving a balanced total knee throughout the entire range of motion leads to improved patient reported outcomes and satisfaction (Hasegawa et al., 2018; Golladay et al., 2019). Sensor-assisted technology allows the surgeon to quantitatively assess and address imbalance through either soft tissue releases or bone recuts (Meneghini et al., 2016; Gustke et al., 2017). However, balancing through soft tissue releases leads to unpredictable gap increments and frequently, to early over-releases (Kwak et al., 2016).
The primary objective of this study was to demonstrate the ability to achieve a quantitatively balanced knee by combining robotic arm (MAKO, Stryker, Kalamazoo, Michigan, USA) and intra-operative load sensors (Verasense, Orthosensor, Inc, Dania Beach, Florida, USA), while avoiding any soft tissue corrections.
During a consecutive and prospective series of 45 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 (Guskte et al). 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 number and type of subsequent corrections needed to achieve quantitative balance.
Of the 45 robotics cases, only 18 (40%) were well-balanced after the initial bone cuts (restricted kinematic alignment adjusted after tensioning collateral ligaments during surgery). In 26 cases, one or two, and rarely, even three bone recut(s) were required to balance the knee. It should be explicitly noted that no soft tissue releases were done for any of the 45 cases. The posterior cruciate ligament was left intact. At the end of the procedure 42 cases (93%) were well balanced in extension, 39 (86%) in flexion and 37 (82%) in flexion and in extension.
Based on this preliminary series, an opportunity to combine multiple technologies to achieve a quantitatively balanced knee through a full range of motion has been demonstrated. This study emphasizes the prospect of achieving a balanced knee joint while only relying on patient-specific bone recuts guided by intra-operative load sensor readings, thus sparing the soft tissues surrounding the knee joint.
The data collected will help make the procedure reproducible, predictable and thus enhance concepts of ligament balancing in total knee arthroplasty, thereby potentially improving patient satisfaction.