Are We Subluxating Knees in Total Knee Arthroplasty? A Cadaveric Investigation

Background: In comparison to coronal, sagittal, and rotational alignment, translational alignment parameters have been widely neglected in total knee arthroplasty (TKA) so far. As there is a certain variable range of possible component placement in mediolateral, ventrodorsal, and proximodistal direction, we hypothesized that relative positions between the femoral and tibial bones are changed after TKA, resulting in a subluxation of knees. Methods: In 10 knees of Thiel-embalmed whole body cadavers, the relative position between the femur and the tibia during passive flexion was measured before and after TKA by means of a navigational device. Results: After TKA, in extension, femoral bones in average shifted 5.3 mm (standard deviation [SD] = 4.0, P = .002) laterally and 2.4 mm (SD = 3.1, P = .038) proximally in extension which, however, decreased throughout flexion. Furthermore, the ventrodorsal femoral position was altered, resulting in a slight relative dorsal shift (2.6 mm, SD = 4.5, P = .099) in extension, which continuously changed into a ventral shift (2.6 mm, SD = 4.3, P = .087) during flexion. Conclusion: The present investigation reveals changed translational parameters between the tibia and the femur after TKA. The resulting subluxation of the knee may be responsible for changed kinematic patterns. These changes in tibofemoral position should be considered in future biomechanical studies. Main reasons for this effect might be a noncentral placement of tibial and femoral implants in relation to the proximal tibial and distal femoral anatomy, obscured intraoperative articular geometry, symmetric implants, and operative techniques. Smaller steps between different component sizes, asymmetric tibial implant design, or individual (anatomic) implants could help to minimize subluxation in TKA. (C) 2016 Elsevier Inc. All rights reserved

Lower Limb Anatomy and Alignment Affect Natural Tibiofemoral Knee Kinematics: A Cadaveric Investigation

Background: During flexion, normal knee kinematics consists of a complex combination of rolling, gliding, and rotation between femur and tibia. Although in vivo studies have shown wide interindividual variability, we hypothesized that knee kinematics is either correlated to the anatomy of the individual knee joint or to the anatomic alignment of the entire lower extremity. Methods: The passive kinematics of 10 healthy knees was assessed in whole cadavers using a commercial computed tomography-free navigation device with intracortical pins. Rotational limb alignment or local anatomic parameters obtained by computed tomography scan or within a navigational procedure were correlated to tibial internal rotation and tibiofemoral abduction during flexion. Results: Mean tibial adduction in full extension was 3.3 degrees (range -2.2 degrees to 7.8 degrees). Tibial abduction and internal rotation showed significant interindividual variability, measuring 3.9 degrees (range -0.8 degrees to 9.7 degrees) and 4.9 degrees (range -3.5 degrees to 14.8 degrees) during flexion. An increase in both the mechanical tibiofemoral axis and the mechanical lateral distal femoral angle correlated with increased tibial internal rotation, whereas a decrease in the mechanical medial proximal tibial angle and an increase in the mechanical tibiofemoral axis were associated with increased tibial adduction. Conclusion: The main finding of the present study is that knee kinematics is influenced by both intraarticular and extra-articular parameters. These results may be of interest in component alignment in total knee arthroplasty, correction of deformities, and malalignment after fracture healing of the lower extremity. Possible relationships should be investigated in future studies. (C) 2016 Elsevier Inc. All rights reserved

Influence of Component Rotation in Total Knee Arthroplasty on Tibiofemoral Kinematics—A Cadaveric Investigation

Background: Physiological tibiofemoral kinematics have been shown to be important for good knee function after total knee arthroplasty (TKA). The purpose of the present study was to investigate the influence of component rotation on tibiofemoral kinematics during knee flexion. We asked which axial component alignment best reconstructs physiological tibiofemoral kinematics and which combinations should be avoided. Methods: Ten healthy cadaveric knees were examined. By means of a navigational device, tibiofemoral kinematics between 0 degrees and 90 degrees of flexion were assessed before and after TKA using the following different rotational component alignment: femoral components: ligament balanced, 6 degrees internal, 3 degrees external rotation, and 6 degrees external rotation in relation to the posterior condylar line; tibial components: self-adapted, 6 degrees internal rotation, and 6 degrees external rotation. Results: Physiological tibiofemoral kinematics could be partly reconstructed by TKA. Ligament-balanced femoral rotation and 6 degrees femoral external rotation both in combination with 6 degrees tibial component external rotation, and 3 degrees femoral external rotation in combination with 6 degrees tibial component internal rotation or self-aligning tibial component were able to restore tibial longitudinal rotation. Largest kinematical differences were found for the combination femoral component internal and tibial component external rotations. Conclusion: From a kinematic-based view, surgeons should avoid internal rotation of femoral components. However, even often recommended combinations of rotational component alignment (3 degrees femoral external and tibial external rotation) significantly change tibiofemoral kinematics. Self-aligning tibial components solely restored tibiofemoral kinematics with the combination of 3 degrees femoral component of external rotation. For the future, navigational devices might help to axially align components to restore patient-specific and natural tibiofemoral kinematics