# The Flexor Retinaculum Connects the Surrounding Structures into the Medial Ankle Complex
## 1 Introduction  
The primary function of the flexor retinaculum (FR) is to maintain the tibialis posterior and the flexor digitorum longus tendons to the underlying medial malleolus during the ankle joint movements [1]. This is supported by clinical observation of patients with injury or insufficiency of the FR after a tear, leading to subluxation of the posterior tibialis tendon over the medial malleolus edge [2]. The FR has a stabilizing and mechanical importance, tethering the tibialis posterior tendon, keeping it in the groove, and preventing dislocation [3]. Furthermore, it is also an essential element of proprioception, described in the literature as a typical fascial feature [1]. The retinaculum proprioception effect was used in the surgical transfer of the inferior extensor retinaculum (IER) to augment the superior peroneal retinaculum [1]. Diversified collagen fiber systems within the fascia, the ligament, or the tendons [4] enable several functional units to be combined into one anatomical structure [5].  
The FR is a broad triangular structure, which extends from the medial malleolus to the posterosuperior aspect of the calcaneus [6]. The anterior extension of the FR is not described in detail. The FR limits the tarsal tunnel from the posterior and medial side and attaches to the medial malleolus, forming the anterior limit of the tarsal tunnel [7]. The tarsal tunnel continues inferiorly tothe sustentaculum tali, the abductor halluces, and the plantar aponeurosis [6]. Projections of the FR divide the tarsal tunnel into smaller compartments for every tendon. The deltoid ligament (DL) is located laterally and inferiorly to the tarsal tunnel; however, there are no data on connections between these structures. Demarcation between retinaculum and other elements of the crural fascia is based on the relative change in thickness of the fascia as they form retinacula [6]. The literature on the anatomy of FR is exceptionally modest or even non-existent. Clinical observation of concomitant injury of the DL and spring ligament (SL) has no anatomical background. On the other hand, observation of concomitant injuries to the lateral ankle ligaments was supported by anatomical studies, where anatomical connections were noticed.  
Concomitant injuries involving several structures are relatively common in the area of the medial malleolus. Injury of the SL has a high association with a tear of the tibialis posterior tendon or sinus tarsi alterations. Likewise, injuries of the posterior tibial tendon associate with plantar fascia tears [8]. A similar phenomenon of concomitant injuries, which are more common than a single structure injury, also occurs in the lateral malleolus area. The anatomical connections that resemble a complex between the anterior talofibrular ligament, the calcaneofibular ligament, and the posterior talofibrular ligament were described previously [9]. Connections of fascial elements, such as the fibulotalocalcaneal ligament (FTCL) and the paratenon, are visible in [PERSON]'s fat pad [10]. This is an example of how the fascia system and the tendon system connects.  
This study aims to test the hypothesis that the structures about the medial malleolus connect through the FR, which is a fascial element, and that these connections can be revealed on routine MRI of the ankle.