In-vivo Comparison of Different Levels of Femoral Rollback in a Primary Total Knee Arthroplasty

Postoperative knee pain is one of the most challenging problems following total knee arthroplasty. Of all the possible complications, the patella-femoral joint is an important cause of postoperative knee pain and prosthetic failure. Nägerl et al. observed that the tibia slides along the femoral surface when the knee is flexed [Nagerlet al., 2009]. Beside the stabilization of the flexion gap, the main task of the posterior cruciate ligament is to initiate the femoral rollback to reduce the patellofemoral pressure. Vice versa, Heyse et al. could show that the patello-femoral pressure rises with the nsuffictency of the posterior cruciate ligament [Heyse et al., 2010]. Pandit et al. measured the physiological rollback in healthy knees and following implantation of currently available TKA. They could show that bonventional TKA are not able to restore the rollback in the natural tibio-femoral joint [Pandit et al., 2005]. Thus it would be important to see if the knee stability in joint replacement reaches the one found in intact or reconstructed knees after surgery. To mimic the femoral rollback a new prosthesis has recently been developed and is about to be introduced to be a new option for total knee arthroplasty. The "Attune Knee System" (DePuy, Warsaw, USA) also has a reduced femoral flange to reduce the patella-femoral contact pressure. The increased rotational stability, the reduced femoral flange and the femoral rollback of the "Attune Knee System" are intended to decrease postoperative knee pain. Different levels of femoral rollback were observed intra-operatively between the Attune and PFC Sigma system. Yoshiya et al. could show the relation between the posterior cruciate ligament with the femoral rollback [Yoshiya et al. 2005]. Therefore, one can hypothesize that different implant designs in combination with the tension of the PCL produce different extents of femoral rollback, ln order to test in-vivo knee kinematics in patients during active movements, we use motion capture, together with combinations of advanced techniques for assessing skeletal kinematics (including sARA [Ehrig et a1.2007], SCoRE [Ehrig et al.2011] \& ocsr [Taytor et at. 2005]), a novet non-invasive approach to evaluate dynamic tibio-femoral motion. The combination of these approaches is now able to provide the accuracy and sensitivity required to analyze movement patterns in a rapid, robust and therefore clinically viable manner. ln order to do so, highly advanced equipment is needed which is available in our laboratory in the Julius Wolff lnstitute. Here, we use an infra-red optical motion capture system (10 T20S cameras, Vicon, Oxford, UK; system accuracy \-0.3-0.5 mm), tracked at120Hz, as well as 2 force plates (AMTI 0R6, Watertown, MA, USA) in order to assess the external forces while performing active movements. With this methodology we are then able to measure the kinematics as well as kinetics in the knee joint [Boeth et al., 2013], especially different levels of femoral rollback in patients with ATTUNE implants, during activities of daily living including walking, jogging, stair ascending/descending, rise a chair, sit down. Furthermore lunge can also be performed with single plane fluoroscopy (BV Pulsera, Philips) with a frequency of 30 Hz. During these measurements, the different extents of femoral rollback in deep flexion (at 105'-125') under weight bearing condiiions will be assessed and compared to the Sigma PFC system. The contact point between the femoral component and the polyethylene inlay will be recorded and compared to standardized postoperative radiographs. Clear specification should be given to the subject in order to avoid unnecessary radiation, for this, at least 3 repetitions without radiation should be performed to guarantee a complete subject's understanding of the procedure. The final position of the foot on the sieps is marked to guarantee a standardization of the procedure. The height of the c-arm of the device is adjusted to the specific shank's height of the subject. During the analysis of the fluoroscopic assessment, model-based RSA software (MEDIS, Leiden, The Netherlands) is used to register CAD models of the meiallic implants to the fluoroscopic images, a registration accuracy of 0.6mm and 0.4' has been reported [Moewis elal.2012].