[Intraoperative Evaluation of Total Knee Arthroplasty: Anatomic and Kinematic Assessment with Trial Components]

The intraoperative use of trial components in total knee arthroplasty (TKA) is of paramount importance to prevent inadequate ligament balance and to achieve optimal position of the definitive components. This review demonstrates an 8-step algorithm to assess the anatomy of the femoral, tibial and patellar component as well as the kinematics of the tibiofemoral and patellofemoral joints. Trial components allow an easy assessment of the anatomic fit of the final implants. Upon the trials insertion, bone coverage and the component overhang should be evaluated. The femoral rotation should be assessed using the transepicondylar axis and for the tibial component rotation assessment, the tibial tuberosity would be the most reliable bony landmark. Addressing the patella, sizing and bone coverage should be thoroughly evaluated. In order to restore physiological kinematics the remnants of the meniscus rim can be used to determine the correct reconstruction of the joint line. A tight extension gap results in limited extension, whereas a tight or unbalanced flexion gap leads to "booking" or "spin-out" of the inlay. The POLO test (pull-out, lift- off) allows an easy assessment of the posterior cruciate ligament tension and the size of the flexion gap as well. To prevent postoperative dislocation and overstuffing, specific tests for correct patellar positioning and tracking support should be performed. The anatomy and kinematics of total knee arthroplasty have to be evaluated by trial components on a routine basis before inserting the final implants in order to identify implant positioning errors and inadequate ligament balance.