Fluoroscopic Analysis of Knee Arthroplasty Kinematics During Deep Flexion Kneeling Kouichi Kanekasu, MD,* Scott A. Banks, PhD,† Shigeru Honjo, MD,* Osanari Nakata, MD,* and Hiromi Kato, MD* Abstract: Achieving deep knee flexion 145° is a goal of many patients receiving knee arthroplasty in Asia and the Middle East, yet it is unknown whether knees with implants move similar to the natural knee in these postures. We studied 18 of 36 consecutively operated knees that were able to flex 145° using fluoroscopic analysis during kneeling to maximum flexion. An average of 9° tibial internal rotation was observed in deep flexion. Posterior condylar translations were observed from 80° to 120° flexion, and the condyles translated forward in flexion beyond 120°. Separation of the condyles from the tibial surface was observed in 9 knees at flexion 130°. Very deep flexion can be achieved and is well accommodated using contemporary posterior-stabilized knee arthroplasty, but the kinematics differ from the intact natural knee. Key words: knee arthroplasty, kinematics, fluoroscopy, deep flexion, implant design. © 2004 Elsevier Inc. All rights reserved. Many fluoroscopic analyses of in ivo kinematics after total knee arthroplasty (TKA) have been re- ported in recent years [1–5]. Many of these reports have analyzed gait or stair activities, but have not assessed knee kinematics under loaded very deep flexion. Several authors have reported fluoroscopic analyses of activities that might be considered “mid- flexion” for many Asian and Middle Eastern life- styles [6 – 8], and have confirmed that patient fac- tors, implant design, surgical technique, and knee kinematics significantly influence maximum knee flexion up to 135° in patients with North American and European lifestyles. Achieving flexion 145° is a goal of many patients receiving TKA but is little documented in the English-language literature. The goal of this study was to characterize knee kinematics in TKA patients who achieved very deep knee flexion. Based on studies of the healthy knee in very deep flexion [9], it was hypothesized that very deep flexion would require tibial internal ro- tation 10°, greater posterior translation of the lateral femoral condyle than the medial condyle, and separation of the articular surfaces in deepest flexion. The study was conducted on Japanese TKA patients for whom Japanese-style sitting, or seiza (Fig. 1A), is a culturally important activity of daily living. Materials and Methods Thirty-six consecutive, cemented TKAs in 24 pa- tients were performed by the same surgeon (K.K.) from December 2000 to May 2001. Posterior cap- sulectomies were performed as part of the posterior cruciate–substituting knee arthroplasty (Scorpio™ From the *Rheumatoid Arthritis Center, Saiseikai Takaoka Hospital, Takaoka, Japan; and †The Biomotion Foundation, West Palm Beach, and the University of Florida, Gainesville, Florida. Submitted September 29, 2003; accepted March 31, 2004. Benefits or funds were received in partial or total support for the research material described in this article from Stryker Japan, a unit of Stryker Howmedica Osteonics. Reprint requests: Scott A. Banks, PhD, Mechanical and Aero- space Engineering, University of Florida, Mail Stop 116250, Gainesville, FL 32611. © 2004 Elsevier Inc. All rights reserved. 0883-5403/04/1908-0009$30.00/0 doi:10.1016/j.arth.2004.03.012 The Journal of Arthroplasty Vol. 19 No. 8 2004 998