A comparison of subtalar joint motion during anticipated medial cutting turns and level walking using a multi-segment foot model T.R. Jenkyn a,b,c, *, R. Shultz a , J.R. Giffin a,d , T.B. Birmingham a,e a Wolf Orthopaedic Biomechanics Laboratory, Fowler Kennedy Sport Medicine Clinic, The University of Western Ontario, London, Ontario, Canada b Department of Mechanical and Materials Engineering, Faculty of Engineering, The University of Western Ontario, London, Ontario, Canada c School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada d Department of Surgery, Schulich School of Medicine and Dentistry, The University of Western Ontario, London, Ontario, Canada e School of Physical Therapy, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada 1. Introduction The ankle–foot complex is functionally composed of the talocrural and subtalar joints between the leg and foot, the joints of the foot itself and the longitudinal and transverse arches. During stance phase, these structures give the lower leg a great range of rotational freedom with respect to the planted foot [1,2] and are loaded to many times body-weight [3]. Sprain of the lateral ankle ligaments accounts for approximately 75% of injuries to the ankle– foot complex [4], which often occur during sporting activities when the ankle–foot musculoskeletal system is over-loaded and fails [5,6]. The most common activity associated with lateral ankle injury is medial cutting turns [7–9] (Fig. 1), which can cause rapid over-inversion of the foot, particularly when the foot is in a plantar-flexed position [5,10,11]. Stacoff et al. [12] studied ankle kinematics during medial turning tasks in barefoot and shoed conditions. This group conducted a video analysis of the ankle–foot complex (treating the foot as a single segment) in the frontal plane and was able to examine relative motion between the foot and shoe. This group concluded that lateral stability of the subtalar joint could be improved with more appropriate shoe design. However, the influence of the joints of the foot, which may play a significant role in lateral ankle sprain, has not been examined during medial cutting turns (Fig. 1). Measurement of foot joint motion requires that multiple foot segments be tracked indepen- dently. Several groups have tracked various configurations of multi-segment foot models with skin-mounted markers [13–16] and markers attached to bone pins [17]. These studies each defined foot segments differently, but common segments have been the hindfoot (rearfoot), forefoot and phalanges. These models have added great insight into the normal and pathological function of Gait & Posture 31 (2010) 153–158 ARTICLE INFO Article history: Received 14 October 2008 Received in revised form 23 September 2009 Accepted 28 September 2009 Keywords: Foot Kinematics Gait analysis Hindfoot Forefoot Ankle Subtalar Joint biomechanics ABSTRACT The weight-bearing in-vivo kinematics and kinetics of the talocrural joint, subtalar joint and joints of the foot were quantified using optical motion analysis. Twelve healthy subjects were studied during level walking and anticipated medial turns at self-selected pace. A multi-segment model of the foot using skin-mounted marker triads tracked four foot segments: the hindfoot, midfoot, lateral and medial forefoot. The lower leg and thigh were also tracked. Motion between each of the segments could occur in three degrees of rotational freedom, but only six inter-segmental motions were reported in this study: (1) talocrural dorsi-plantar-flexion, (2) subtalar inversion–eversion, (3) frontal plane hindfoot motion, (4) transverse plane hindfoot motion, (5) forefoot supination–pronation twisting and (6) the height-to- length ratio of the medial longitudinal arch. The motion at the subtalar joint during stance phase of walking (eversion then inversion) was reversed during a turning task (inversion then eversion). The external subtalar joint moment was also changed from a moderate eversion moment during walking to a larger inversion moment during the turn. The kinematics of the talocrural joint and the joints of the foot were similar between these two tasks. During a medial turn, the subtalar joint may act to maintain the motions in the foot and talocrural joint that occur during level walking. This is occurring despite the conspicuously different trajectory of the centre of mass of the body. This may allow the foot complex to maintain its function of energy absorption followed by energy return during stance phase that is best suited to level walking. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author at: Department of Mechanical and Materials Engineering, Spencer Engineering Building, Room 2075, The University of Western Ontario, London, Ontario, Canada N6A 5B9. Tel.: +1 519 661 2111x88339; fax: +1 519 661 3020. E-mail address: tjenkyn@eng.uwo.ca (T.R. Jenkyn). Contents lists available at ScienceDirect Gait & Posture journal homepage: www.elsevier.com/locate/gaitpost 0966-6362/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2009.09.016