Effects of foot orthoses on the work of friction of the posterior tibial tendon Takaaki Hirano a,c , Matthew B.A. McCullough a,c , Harold B. Kitaoka b,c , Kazuya Ikoma a,c , Kenton R. Kaufman b,c, * a Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic, Rochester, MN 55095, USA b Department of Biomedical Engineering, College of Medicine, Mayo Clinic, Rochester, MN 55095, USA c Department of Orthopedic Surgery, College of Medicine, Mayo Clinic, Rochester, MN 55095, USA article info Article history: Received 2 December 2008 Accepted 22 July 2009 Available online xxxx Keywords: Foot Ankle Work of friction Orthotics Biomechanics abstract Background: Posterior tibial tendon dysfunction is a significant contributor to flatfeet. Non-operative treatments, like in-shoe orthoses, have varying degrees of success. This study examined changes to the work of friction of the posterior tibial tendon under three conditions: intact, simulated flatfoot, and flat- foot with an orthosis. It was hypothesized that work of friction of the posterior tibial tendon would sig- nificantly increase in the flatfoot, yet return to normal with an orthosis. Changes to bone orientation were also expected. Methods: Six lower limb cadavers were mounted in a foot simulator, that applied axial and a posterior tibial tendon load. Posterior tibial tendon excursion, gliding resistance, and foot kinematics were moni- tored, and work of friction calculated. Each specimen moved through a range of motion in the coronal, transverse, and sagittal planes. Findings: Mean work of friction during motion in the coronal plane were 0.17 N cm (SD 0.07 N cm), 0.25 N cm (SD 0.09 N cm), and 0.23 N cm (SD 0.09 N cm) for the intact, flatfoot, and orthosis conditions, respectively. Motion in the transverse plane yielded average WoF of 0.36 N cm (SD 0.28 N cm), 0.64 N cm (SD 0.25 N cm), and 0.57 N cm (SD 0.38 N cm) in the same three conditions, respectively. The average tibio-calcaneal and tibio-metatarsal valgus angles significantly increased in the flatfoot condition (5.8° and 9°, respectively). However, the orthosis did slightly correct this angle. Interpretation: The prefabricated orthosis did not consistently restore normal work of friction, though it did correct the flatfoot visually. This implies that patients with flatfeet may be predisposed to developing posterior tibial tendon dysfunction due to abnormal gliding resistance, though bone orientations are restored. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Posterior tibial tendon dysfunction (PTTD) has been recognized as the most common cause of acquired flatfoot deformity in adults (Augustin et al., 2003; Myerson and Corrigan, 1996). It is reported that approximately 50% of patients with PTTD have a history of trauma (Mann and Thompson, 1985b). Symptoms manifest them- selves as pain, swelling, tenderness, and increased warmth about the posteromedial hindfoot and ankle, weak supination strength, difficulty completing the single heel rise tests, and eventually pro- gression to a full flatfoot deformity. Patients who are not effec- tively treated during the early stages of PTTD risk progression to a severely deformed and rigid hindfoot, advanced hindfoot arthri- tis, calcaneofibular impingement, ankle instability, and ankle arthritis. Late phases of PTTD present several problems ranging from synovitis of the tendon without anatomic abnormality nor collapse of the longitudinal arch, severe valgus of the heel, and abduction of the forefoot (Mann and Thompson, 1985b). It was also reported that excessive weight appears to accelerate flatfoot devel- opment, due to increased repetitive load absorbed by the postero- medial soft tissues (Holmes and Hansen, 1993). Because of hypovascularity and inhomogeneous distribution of blood vessels (Petersen and Hohmann, 2001), restoration of posterior tibial ten- don (PTT) function after damage can be difficult. If untreated the tendon attenuates, elongates, and thickens causing spontaneous tendon ruptures (Johnson, 1983; Mosier et al., 1999). The prevalence of severe flatfoot as well as the link between PTTD and flatfeet has prompted several investigations into treat- ment options for PTTD. Unfortunately comparisons across in vivo studies cannot be made, due to participant differences. Cadaveric models of flatfeet have been described in the literature (Kitaoka et al., 1998; Deland et al., 1992; Friedman et al., 2001). These stud- ies are important because they allowed longitudinal comparison of the affects of flatfeet. 0268-0033/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.clinbiomech.2009.07.009 * Corresponding author. Address: Mayo Clinic, Charlton North L110K, 200 First St. SW, Rochester, MN 55095, USA. E-mail address: kaufman.kenton@mayo.edu (K.R. Kaufman). Clinical Biomechanics xxx (2009) xxx–xxx Contents lists available at ScienceDirect Clinical Biomechanics journal homepage: www.elsevier.com/locate/clinbiomech ARTICLE IN PRESS Please cite this article in press as: Hirano, T., et al. Effects of foot orthoses on the work of friction of the posterior tibial tendon. J. Clin. Biomech. (2009), doi:10.1016/j.clinbiomech.2009.07.009