Anteroposterior Knee Stability During Stair Descent Kyle A. Borque, MD a , Jonathan E. Gold, BS b , Stephen J. Incavo, MD c , Rupal M. Patel, MD c , Sabir E. Ismaily, BS b , Philip C. Noble, PhD a, b a Baylor College of Medicine, Houston, Texas b The Institute of Orthopedic Research Education, Houston, Texas c Houston Methodist Hospital, Houston, Texas abstract article info Article history: Received 31 July 2014 Received in revised form 9 January 2015 Accepted 11 January 2015 Keywords: anteroposterior knee stability total knee arthroplasty cruciate-retaining inserts cruciate-sacrificing inserts posterior-stabilizing tibial inserts This study examined the influence of tibio-femoral conformity on anteroposterior (AP) knee stability during stair descent, particularly with a dished cruciate sacrificing (CS) design. A joint simulator simulated stair descent of cadaveric knees. Tibio-femoral displacement was measured. Knees were tested in intact, ACL-deficient, and TKA with cruciate-retaining (CR), CS and posterior-stabilizing (PS) inserts. Loading during stair descent simula- tion caused femur displacement anteriorly prior to quadriceps contraction. Quadriceps contraction reestablished the initial femoral AP position. During simulated stair descent, AP stability was restored using PS, CR or CS inserts with an intact PCL. The CS design without the PCL did not provide AP stability. Increasing quadriceps force to re- store AP stability may explain the clinical findings of pain and fatigue experienced by some patients after TKA. © 2015 Elsevier Inc. All rights reserved. Growing attention on the functional outcome of a total knee arthroplasty (TKA) has shown that many patients experience limita- tions when attempting to perform high demand activities considered normal for age-matched peers. This is primarily because of knee symp- toms [1]. For the TKA patient, “high demand” activities are typically those imposing impact loads on the knee or those requiring extreme range-of-motion [2]. In practice, activities leading to apprehension and discomfort following TKA more typically involve instability of the joint, in which significant transverse or torsional forces are applied with relatively low joint compression forces [3]. Under these conditions, normal muscle contraction is accompanied by a shift in the relative po- sitions of the bones. This occurs to maintain the balance of external forces as well as the internal restraints provided by the ligaments and the articular surfaces. Following TKA, instability is most often reported during activities causing significant transverse or torsional forces that are supported by the joint, with relatively low joint compression forces. Such activities in- clude stair-descent and walking on sloped or uneven surfaces [4–9]. Au- thors have hypothesized that symptoms arise during these activities because patients must compensate for the inherent instability of the knee prosthesis by varying the force of contraction of antagonistic muscle groups crossing the joint, most commonly the quadriceps and hamstring muscles [10]. Though this is expected to reduce subluxation of the femur in response to loading, the increased demand on the mus- culature may lead to pain and fatigue. Restoring stability of the normal knee is a challenge for total knee prostheses, as the original stability of the knee is provided by increased conformity of articulating surfaces compensating for the sacrifice of one or both cruciate ligaments [11]. In practice, this can be difficult to achieve in every knee. Variations in the shape of articulating surfaces and the anatomic location and stiffness of ligaments can lead to differ- ences in the resistance of each knee to translational and rotational forces [11–13]. Previous studies comparing AP knee stability before and after TKA have focused on tibio-femoral kinematics during squatting and lunging [14,15]. In this study, we have utilized a novel cadaveric simula- tion to assess the capacity of cruciate–retaining and substituting TKA to restore the natural stability of the knee during stair descent - in the presence of physiologic loading of the flexors and extensors. We were particularly interested in the role of the PCL during this high demand ac- tivity. In addition to posterior cruciate retaining (CR) and posterior sta- bilized (PS) TKA designs, we also examined a more dished tibial insert. This dished insert, referred to as a cruciate sacrificing (CS) design, is de- signed to provide more AP stability in the absence of a functional PCL. The CS insert used in the study was conforming in both medial and lat- eral compartments of the insert (Triathlon, Stryker, Mahwah NJ) [16]. This study was designed to answer the following questions: 1. During stair descent, does contraction of the quadriceps alter tibio-femoral translation (AP) and rotation (internal/external) in the normal knee? The Journal of Arthroplasty 30 (2015) 1068–1072 One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to http://dx.doi.org/10.1016/j.arth.2015.01.011. Reprint requests: Stephen Incavo, MD, Houston Methodist Hospital, 6565 Fannin St/ Houston, TX 77030. http://dx.doi.org/10.1016/j.arth.2015.01.011 0883-5403/© 2015 Elsevier Inc. All rights reserved. Contents lists available at ScienceDirect The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org