Function of ankle ligaments for subtalar and talocrural joint stability during an inversion movement – an in vitro study

Li et al. Journal of Foot and Ankle Research https://doi.org/10.1186/s13047-019-0330-5 (2019) 12:16 RESEARCH Open Access Function of ankle ligaments for subtalar and talocrural joint stability during an inversion movement – an in vitro study Lu Li1* , Albert Gollhofer1, Heinz Lohrer1,2,3, Nadja Dorn-Lange4, Guiseppe Bonsignore4 and Dominic Gehring1 Abstract Background: The lateral ankle ligament complex consisting of the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL) and the posterior talofibular ligament (PTFL) is known to provide stability against ankle joint inversion. As injuries of the ankle joint have been reported at a wide range of plantarflexion/dorsiflexion angles, the aim of the present study was to evaluate the stabilizing function of these ligaments depending on the sagittal plane positioning of the ankle joint. Methods: Eight fresh-frozen specimens were tested on a custom-built ankle deflection tester allowing the application of inversion torques in various plantarflexion/dorsiflexion positions. A motion capture system recorded kinematic data from the talus, calcaneus and fibula with bone-pin markers during inversion movements at 10° of dorsiflexion, at neutral position and at plantarflexion 10°. ATFL, CFL and PTFL were separately but sequentially sectioned in order to assess the contribution of the individual ligament with regard to ankle joint stability. Results: Joint- and position-specific modulations could be observed when the ligaments were cut. Cutting the ATFL did not lead to any observable alterations in ankle inversion angle at a given torque. But subsequently cutting the CFL increased the inversion angle of the talocrural joint in the 10° plantarflexed position, and significantly increased the inversion angle of the subtalar joint in the 10° dorsiflexed position. Sectioning of the PTFL led to minor increases of inversion angles in both joints. Conclusions: The CFL is the primary ligamentous stabilizer of the ankle joint against a forced inversion. Its functioning depends greatly on the plantar−/dorsiflexion position of the ankle joint complex, as it provides the stability of the talocrural joint primarily during plantarflexion and the stability of the subtalar joint primarily during dorsiflexion. Keywords: Lateral ankle ligament complex, Ankle stability, Ankle inversion restriction, Biomechanics Introduction Epidemiological data indicate that ankle injuries represent the most frequent type of sport-related injuries [1]. There exists overwhelming evidence that most of the ankle injuries affect the ligaments [2] and that approximately 85% of those injuries are lateral ankle sprains [3]. The aetiology for injuries of the lateral ankle joint typically comprises excessive inversion, often combined with a pronounced plantarflexion and internal rotation of the ankle joint complex [4]. It has been shown that an initial * Correspondence: 1 Department of Sport and Sport Science, University of Freiburg, Schwarzwaldstraße 175, 79117 Freiburg, Germany Full list of author information is available at the end of the article sprain can impair the function of the ankle joint complex in the long term, which is referred to as chronic ankle instability [5]. From an anatomical perspective, the lateral ankle ligament complex consists of the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL) and the posterior talofibular ligament (PTFL). Epidemiologic surveys indicate that the ATFL is the ligament that is injured in 85% of all ankle sprain ligament injuries, while the CFL is involved in 35% and the PTFL in 12% [6]. In trying to identify why the individual ligaments are affected during an ankle sprain with different rates, their functional roles and their mechanical properties must be taken into consideration. Most of the current information about the © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Li et al. Journal of Foot and Ankle Research (2019) 12:16 functioning of the ankle ligament originates from in-vitro studies, where custom-made devices were developed to study the biomechanics of the ankle joint while analysing the differential functional importance of the ligaments. Researchers typically applied inversion-eversion stimuli and/or plantarflexion-dorsiflexion in predefined positions of the ankle joint. The biomechanical function is then studied by dissecting a specific ligament and estimating its contribution to stabilizing the ankle joint [7–11]. Increased knowledge about the function of the specific ligaments revealed that the ATFL seems to be the most affected ligament [12, 13], because its functional role is to restrict both plantarflexion and inversion movements [14] and because the maximal tension until failure is quite low [8]. Moreover it has been shown that a certain inversion torque, applied at the fixed foot, increases the posterior tibial displacement by a factor of 2 when the ATFL is dissected [15]. In addition to the ATFL, the CFL seems to resist ankle inversion, as cutting this ligament led to an increased range of inversion [9]. Applying an inversion loading following a dissection of both ATFL and CFL respectively increased the range of motion and decreased the end-range stiffness when compared with the intact and solely ATFL-sectioned ankles [16]. Furthermore, evidence exists showing that a dissection of the CFL causes significant range of motion changes regarding all three planes in the subtalar joint [10]. Thus, it seems that the CFL plays a key role in the lateral stabilization of both the ankle and the subtalar joint. The functional properties of the PTFL were analysed by Ozeki and Kitaoka, who concluded that the PTFL is an important stabilizer especially when the ankle was in a dorsiflexed postion [17]. Previous research has also shown that the strain of the PTFL increases in dorsiflexion (DF) and plantarflexion (PF), but is only minimally affected by ankle inversion [18]. In summary, the PTFL seems to play a supplementary role in lateral ankle stability, especially when the ATFL and CFL are intact [19]. Although it is possible to draw important conclusions about the ligament function from the above mentioned in-vitro studies, specific methodological restrictions have to be considered. First, some of the papers selectively focused on only one specific ligament of the ankle and its defined functional role [9, 14, 15, 18, 19] whi (...truncated)