c o m p u t e r m e t h o d s a n d p r o g r a m s i n b i o m e d i c i n e 1 1 3 ( 2 0 1 4 ) 126–132 j o ur na l ho me pag e: www.intl.elsevierhealth.com/journals/cmpb A computer assessment of the effect of hindfoot alignment on mechanical axis deviation Naven Duggal a , Gabrielle M. Paci b,1 , Abhinav Narain b,1 , Leandro Grimaldi Bournissaint b,1 , Ara Nazarian b,∗ a Department of Orthopaedic Surgery, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02215, United States b Center for Advanced Orthopaedic Studies, Beth Israel Deaconess Medical Center, 99 Brookline Avenue, Boston, MA 02215, United States a r t i c l e i n f o Article history: Received 12 October 2012 Received in revised form 19 August 2013 Accepted 13 September 2013 Keywords: Mechanical axis deviation Lower extremity alignment Hindfoot alignment Total knee arthroplasty Weight-bearing axis a b s t r a c t Lower limb malalignment is a common cause of disability that increases risk of osteoarthritis (OA). Treatment of OA may require an osteotomy or arthroplasty, which mandate accurate evaluation of mechanical loading on the limbs to achieve optimal alignment and minimal implant wear. Surgical planning uses a conventional method of mechanical axis deviation (MADC) measured from the center of the femoral head to the center of the ankle. This method fails to account for hindfoot deformity distal to the ankle. We used a computer model to compare MADC with the ground mechanical axis deviation (MADG), drawn from the center of the hip to the ground reaction point. Average anatomic measurements were analyzed with a range of knee and hindfoot angle variation in single leg stance, double leg stance, toe off and heel strike. MADG was consistently higher than MADC, suggesting a more complete estimate of weight-bearing axis that considers hindfoot deformity. © 2013 Elsevier Ireland Ltd. All rights reserved. Introduction Osteoarthritis (OA) is the most common form of joint dis- ease and often leads to slowly progressive disability in the elderly. [1]. Approximately 27 million people in the United States are currently affected by OA. Moreover, Americans have a 46% lifetime risk of developing OA of the knee [2]. Numerous biomechanical factors, including malalignment of the lower limbs, are associated with increased force across the joints leading to higher incidence and progression of OA of the knee and the ankle [3]. This malalignment can take the form of varus angulation of the distal segment toward the midline ∗ Corresponding author at: Beth Israel Deaconess Medical Center, Center for Advanced Orthopaedic Studies, 330 Brookline Avenue, RN 115, Boston, MA 02215, United States. Tel.: +1 617 667 8512; fax: +1 617 667 7175. E-mail address: anazaria@bidmc.harvard.edu (A. Nazarian). 1 These authors have contributed equally to the work. or valgus angulation of the distal segment away from the midline. At the knee, varus malalignment has been shown to initiate OA, while both varus and valgus malaligments are associated with increased progression of already existent medial and lateral joint disease respectively. This is thought to be due to shifts in the weight-bearing or mechanical axis of the lower extremity from the anatomic axis [4]. Initial treat- ment for knee OA may include non-operative measures such as physical therapy, weight loss, and orthotics. Symptomatic degeneration that is refractory to non-operative measures is commonly treated surgically with total knee arthroplasty (TKA). 0169-2607/$ – see front matter © 2013 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cmpb.2013.09.010