In Vivo Comparison of Knee Kinematics Before and After High-Flexion Posterior Cruciate-Retaining Total Knee Arthroplasty Atsushi Kitagawa, MD,* Nobuhiro Tsumura, MD,* Takaaki Chin, MD,* Kazuyoshi Gamada, PhD, y Scott A. Banks, PhD, z and Masahiro Kurosaka, PhD § Abstract: The objectives of this study were to compare preoperative and postoperative knee kinematics for subjects implanted with flexion-enhanced posterior cruciate-retaining total knee arthroplasty during deep flexion and to examine flexion performance of the prosthesis design. Three-dimensional kinematics was analyzed by fluoroscopic examinations of subjects using a single- plane model-image registration technique. Preoperatively, knee kinematics demonstrated small posterior femoral translation and limited axial rotation. These motions differed significantly from patterns previously reported for normal knees. Postoperatively, flexion performance was maintained, averaging 130°, and kinematic patterns were similar to preoperative patterns. Although total knee arthroplasty can reduce pain and maintain functional performance, it appears that the characteristics of varus arthritic knee mechanics persist after arthroplasty. Keywords: total knee arthroplasty, posterior cruciate ligament, knee kinematics, deep flexion. © 2010 Elsevier Inc. All rights reserved. The ability to flex beyond 120° is critical for participation in normal kneeling and squatting activities commonly performed in the Far and Middle East. However, many studies report maximum flexion averages less than 120° after posterior cruciate ligament-retaining (PCR) total knee arthroplasty (TKA) [1-3]. Various factors are reported to limit flexion with PCR-TKA, including direct impingement of the tibial insert against the back of the femur, insufficient posterior femoral translation, de- creased posterior condylar offset, an elevated posterior lip on the tibial insert, and insufficient posterior tibial slope [1,4]. Interestingly, a previous study has reported preoperative flexion is the best predictor of postoperative flexion [5], but there currently is little information concerning in vivo kinematic changes of prosthetic knees from osteoarthritic ones in the same subject during deep knee flexion. In vitro studies have shown TKA can maintain nearly 80% of the natural posterior femoral translation up to 150° flexion, but posterior cruciate ligament integrity had little effect on knee kinematics at high flexion [6]. In vivo studies have often observed that knees with PCR-TKA exhibit anterior femoral translation during terminal flexion, so-called paradoxical translation, which indicates nonphysiologic posterior cruciate ligament function [1,7,8]. Recently, a number of new TKA designs have been introduced to facilitate more normal knee kinematics and provide enhanced flexion with PCR-TKA. The purpose of this study was to address 2 primary questions. First, do flexion-enhanced PCR-TKA designs improve flexion performance compared to traditional PCR-TKA designs? Second, how do preoperative and postoperative knee kinematics compare in patients having varus osteoarthritis treated with PCR-TKA? Given that many studies report abnormal kinematics after TKA, it would seem important to know if these motion patterns are established before TKA. To answer these questions, we investigated in vivo kinematics during maximum flexion for subjects implanted with a TKA and compared preoperative and postoperative kinematics, using fluoroscopic examination, a single- plane shape-matching technique, of subjects. Methods In vivo kinematics was assessed in 10 subjects who were implanted with flexion-enhanced PCR-TKA From the *Department of Orthopedic Surgery, Hyogo Rehabilitation Center Hospital, Hyogo, Japan; yDepartment of Physical Therapy Hiroshima International University, Hiroshima, Hiroshima, Japan; zDepartment of Mechanical and Aerospace Engineering, University of Florida Gainesville, Florida; and §Department of Rehabilitation Science, Kobe University Graduate School of Medicine, Hyogo, Japan. Submitted July 31, 2008; accepted July 8, 2009. No benefits or funds were received in support of the study. Reprint requests: Atsushi Kitagawa, MD, Hyogo Rehabilitation Center Hospital, 1070 Akebono-cho, Nishi-ku, Kobe 651-2181, Japan. © 2010 Elsevier Inc. All rights reserved. 0883-5403/2506-0020$36.00/0 doi:10.1016/j.arth.2009.07.008 964 The Journal of Arthroplasty Vol. 25 No. 6 2010