The Biomechanical Effect of Increased Valgus on Total Knee Arthroplasty: A Cadaveric Study Brandon J. Bryant, MD, Justin U. Tilan, MD, Michelle H. McGarry, MS, Nobuyuki Takenaka, MD, PhD, William C. Kim, MD, Thay Q Lee, PhD Orthopaedic Biomechanics Laboratory VA Long Beach Healthcare System, California University of California, Irvine abstract article info Article history: Received 10 December 2012 Accepted 1 September 2013 Keywords: total knee arthroplasty valgus tibiofemoral contact patellofemoral contact MCL strain The effects of valgus load on cadaveric knees following total knee arthroplasty (TKA) were investigated using a custom testing system. TKAs were performed on 8 cadaveric knees and tested at 0°, 30°, and 60° knee flexion in both neutral and 5° valgus. Fuji pressure sensitive film was used to quantify contact areas and pressures and MCL strain was determined using a Microscribe digitizing system. Lateral tibiofemoral pressures increased (P b 0.05) at all knee flexion angles with valgus loading. Patellofemoral contact characteristics did not change significantly (P N 0.05). Significant increases in strain were observed along the anterior and posterior border of the MCL at all knee flexion angles. These findings suggest that valgus loading increases TKA joint contact pressures and MCL strain with increasing knee flexion which may increase implant instability. Published by Elsevier Inc. Restoration of the mechanical axis in total knee arthroplasty (TKA) ensures both proper weight bearing and good long-term functional outcome. This mechanical axis traditionally runs from the center of the femoral head through the center of the ankle. However, sagittal balancing intra-operatively and hindfoot malalignment have been shown to produce a valgus stress and therefore are important when determining the overall loading axis of the lower limb [1–4]. The kinetic chain of the leg can be disrupted by pes planus, hindfoot valgus and hyperpronation of the forefoot [5]. Teitge et al noted that increased pronation of the foot resulted in a decreased lateral thrust of the knee however, it also caused increased loading on the lateral tibiofemoral joint with genu valgum [6]. They concluded that this mechanism accounted for a more frequent association of pronated feet, posterior tibial tendon rupture, and genu valgus [6]. Previous kinematic and motion studies have shown that a lateral wedge prosthesis and excessive rearfoot pronation both can create increased valgus moments at the knee [7,8]. Also, in those patients with Rheumatoid Arthritis, studies have observed the association of hindfoot malalignment, which may not be considered in a primary TKA [2,4,8–10]. In a prospective study of TKA in the osteoarthritic knee, the authors demonstrated that hindfoot malalignment can persist postoperatively which causes a lateral shift of the weight- bearing axis [4]. Further, in an analysis of TKA revisions, Meding et al found that a high incidence of the total revisions was associated with posterior tibial tendon insufficiency, which can cause a hindfoot valgus deformity [11]. Valgus forces also affect the medial collateral ligament, which serves as the primary restraint to valgus angulation and which can be attenuated over time as a result of repetitive valgus forces. The patellofemoral joint should also be considered when examining valgus forces. The Q angle, defined as the angle between a line drawn from the ASIS through the center of the patella and a line drawn from the center of the patella through the tibial tuberosity, is a guide to help maintain proper patella tracking, which is one of the most common complications of TKA. Changes in the Q angle caused by repetitive valgus forces can create maltracking, pain and prosthetic wear. While restoration of mechanical alignment is paramount in TKA, how valgus forces affect a prosthetic knee in varying degrees of flexion has yet to be described. We hypothesized that valgus loading would alter joint contact characteristics as well as increase strain in the MCL. To that end, we performed TKAs in cadaveric knees in order to assess MCL strain and the contact characteristics of the tibiofemoral and patellofemoral joints in both neutral and in five degrees of valgus. Materials and Methods Specimen Preparation Eight fresh frozen cadaver knees (5 right, 3 left) ranging in age from 73 to 85 years were obtained and stored at -20 °C. All specimens were macroscopically intact without gross pathology or evidence of prior surgery. A posterior cruciate ligament (PCL) sacrificing TKA was performed using the Foundation Knee System (DJO Surgical, Austin, TX). All eight total knee arthroplasties were The Journal of Arthroplasty 29 (2014) 722–726 The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2013.09.003. Reprint requests: Thay Q. Lee, PhD Orthopaedic Biomechanics Laboratory VA Long Beach Healthcare System (09/151) 5901 East 7th. Street Long Beach, CA 90822. 0883-5403/2904-0020$36.00/0 – see front matter. Published by Elsevier Inc. http://dx.doi.org/10.1016/j.arth.2013.09.003 Contents lists available at ScienceDirect The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org