Kinematic Differences Between Gender Specific and Traditional Knee Implants Stefan K. Saevarsson MSc a , Gulshan B. Sharma PhD a , Heiko Ramm MS c , Robert Lieck MS c , Carol R. Hutchison MD, FRCSC b , Jason Werle MD, FRCSC b , Sigrun Matthiasdottir BSc a , Spencer J. Montgomery DipAST a , Carolina I. Romeo a , Stefan Zachow PhD c , Carolyn Anglin PhD, PEng a a Biomedical Engineering and the McCaig Institute for Bone and Joint Health, University of Calgary, Canada b Orthopaedic Surgery and the McCaig Institute for Bone and Joint Health, University of Calgary, Canada c Zuse Institute Berlin, Germany abstract article info Article history: Received 21 August 2012 Accepted 16 January 2013 Available online xxxx Keywords: total knee arthroplasty gender specific implants kinematics patella prosthesis design imaging In the ongoing debate about gender-specific (GS) vs. traditional knee implants, there is limited information about patella-specific outcomes. GS femoral component features should provide better patellar tracking, but techniques have not existed previously to test this accurately. Using novel computed tomography and radiography imaging protocols, 15 GS knees were compared to 10 traditional knees, for the 6 degrees of freedom of the patellofemoral and tibiofemoral joints throughout the range of motion, plus other geometric measures and quality of life (QOL). Significant differences were found for patellar medial/lateral shift, where the patella was shifted more laterally for the GS femoral component. Neither group demonstrated patellar maltracking. There were no other significant differences in this well-functioning group. © 2013 Elsevier Inc. All rights reserved. Gender-specific (GS) implants for total knee arthroplasty (TKA) have received considerable attention and controversy recently, yet little attention has been paid to the patellofemoral joint. Recent studies have found lower functional scores, patellar scores and stairs scores in women compared to men [1,2]. Patellar kinematics may also differ in females before and after total knee arthroplasty, with greater lateral tilt compared to males shown during passive intraoperative flexion [3]. Design features of the GS implants, which include a more laterally-oriented femoral groove and a thinner anterior flange (Fig. 1), have the potential to improve patellar tracking. The design differences between GS and traditional implants are intended to reflect anatomical differences between male and female knees. Female knees on average have narrower mediolateral di- mensions [4,5], a more trapezoidal distal femur [6], and the patellofemoral groove is angled more externally relative to the femoral epicondylar line [5] compared to male knees. GS implants have therefore been designed with a reduced mediolateral to anteroposterior (ML/AP) aspect ratio, a thinner anterior flange and a larger trochlear groove angle compared to their traditional knee component (Fig. 1) [7]. One of the main goals of fitting the anatomy better is to require fewer intraoperative adjustments. Adjustments include either down- sizing or upsizing the component. Downsizing the component requires a change to the AP positioning, affecting the flexion and extension gaps, which can result in an unstable or stiff knee; it also risks leaving more bone exposed. Upsizing the component risks overstuffing the joint and having the femoral component overhang medially or laterally. Reducing the ML/AP ratio of the femoral component makes it theoretically possible to reduce mediolateral overhang in women [8], although this may or may not be achieved in practice [9,10]. By having a thinner anterior flange the risk of overstuffing the knee is reduced. Overstuffing the knee can reduce the range of motion (ROM) and increase the likelihood of anterior knee pain [11]. A larger trochlear groove angle accommodates the larger quadriceps (Q)-angle of females, which could thereby provide better patellar tracking [7]. Studies comparing the clinical outcome of GS implants to traditional implants have not found an improved outcome among women with GS implants, based on traditional scores [12,13]. However, there are several factors that traditional scores do not include, especially anterior knee pain (AKP). Factors beyond the traditional measures should be investigated further, especially given that approximately 18% of patients are not satisfied with their TKA [14]. One of the factors that affects AKP is patellar tracking, where patellar maltracking has been defined as shift N 5 mm or tilt N 5° [15]. The Journal of Arthroplasty xxx (2013) xxx–xxx The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2013.01.021. Reprint requests: Carolyn Anglin PhD, PEng, Department of Civil Engineering, University of Calgary, 2500 University Dr. NW, Calgary, AB, T2N 1N4. 0883-5403/0000-0000$36.00/0 – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2013.01.021 Contents lists available at SciVerse ScienceDirect The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org Please cite this article as: Saevarsson SK, et al, Kinematic Differences Between Gender Specific and Traditional Knee Implants, J Arthroplasty (2013), http://dx.doi.org/10.1016/j.arth.2013.01.021