CORR Insights®: Is There a Force Target That Predicts Early Patient-reported Outcomes After Kinematically Aligned TKA?

摘要

Where Are We Now? The current study by Shelton and colleagues [9] examines the intersection of two pressing issues—subject-specific component alignment and measurements of tibiofemoral compartment forces—and may illustrate that those two issues were never intended to intersect in the first place. Much of the content of this paper can be attributed to the mixed results associated with computer-assisted tools like robotic-assisted surgery and surgical navigation systems. Less than two decades ago, such surgical systems were on the cutting-edge of potentially improving the accuracy and precision of implant alignment. While the systems led to more-accurate component alignment with fewer outliers [1, 10], the best evidence we have suggests that such improvement in alignment does not result in improved patient-reported outcomes or survivorship [3, 6]. Combined with the cost of those systems and the increase in surgical time associated with their use [6], enthusiasm for computer-assisted tools has cooled in recent years. Those concerns led clinical researchers to contemplate other ways to improve alignment and refine surgical techniques. One such approach, the use of kinematic alignment (KA), aligns the femoral and tibial components to restore the native joint lines and native alignments of the limb and knee without ligament release [2, 9]. Since the KA approach is based on individual anatomy, its ideal component alignment varies from patient to patient and contrasts the alignment goals of navigation systems where the center of femoral head, the center of the knee, and the center of the ankle are within ± 3° of a straight line. Wireless communication technology and sensors like the VerasenseTM (Orthosensor Inc, Dania Beach, FL, USA), are other innovations that provide objective measures of tibiofemoral compartment contact forces that serve as a measure of ligamentous knee laxity. As Shelton and colleagues note, such objective measurements of tibiofemoral compartment forces can theoretically be applied to all patients [9]. Thus, the authors set out to determine whether there is a single quantifiable measure of laxity that can be applied to subject-specific component alignment approaches. The authors concluded that they could not establish a threshold loading level for KA that was associated with better outcomes. Where Do We Need To Go? After reading the study, several questions remain. First, what if these instrumented sensors are making the wrong kind of measurements? The tibiofemoral contact forces are typically recorded during a passive ROM or with the knee at discrete flexion angles [9]. However, neither of those conditions place the collateral ligaments under a substantial load. In the 1970s, Markolf and colleagues [4] argued that “clearly, continuous recordings of force-displacement and moment-rotation relationships will give more information on knee stability than one measurement of the deformation at a single load level” [4]; the senior author on the present study has performed similar in-vivo characterizations of knee laxity [5]. I contend (and future studies are needed to confirm or refute this contention) that such measurements of angular or linear displacement under a load would be a more-appropriate indicator of the laxity of the knee than tibiofemoral contact and be a better predictor of how the knee would behave under a varus thrust, or during challenging activities like stepping down from a curb or rising from a chair. A new generation of surgical tools is needed for measuring knee kinematics and laxity. These tools should have the ability to record component alignment and the motion of the knee under a known load that is applied by the surgeon in both the osteoarthritic knee and following component implantation. Early versions of such tools already exist for use in cadavers [7, 8, 11]. Second, what if the measurements are being made at the wrong time during the surgery? All of these instrumented tibial trays interface