# The Flexor Retinaculum Connects the Surrounding Structures into the Medial Ankle Complex
## 4 Discussion
We could not find any research regarding connections between the FR and other ligamentous and non-ligamentous structures in the medial ankle area. Given the presence of connections in the lateral malleolus area and Kager's fat pad, there is no reason to assume that similar interconnectionsare not present on the medial side of the ankle joint. This study aimed to prove this hypothesis based on the clinical observation that a DL tear may be combined with the SL and a posterior tibial tendon injury [20]. Naturally, a similar injury mechanism may be the underlying cause; however, considering previous studies, the presence of connections may also contribute to more concomitant injury [9; 10]. A tear or dysfunction of one structure may influence the other structures, leading to medial or multidirectional ankle instability [13; 20; 21]. One of the essential functions of the medial ankle structure is to restrain against valgus sloping and anterior and lateral translation of the talus [13]. Joining smaller ligament structures into larger anatomical-functional units provides better stability of the ankle joint by causing greater diversification of the direction of the collagen fibers. The DL is a broad and robust ligament that connects the medial malleolus with the navicular bone, the talus, and the calcaneus [13]. The superficial part of the DL blends with the FR at the common attachment medial malleolus [3; 6; 22]. The presence of the DL's anatomical and functional components results in the striated MRI appearance of the DL, which should not be confused with a tear [12]. Anatomical literature distinguishes the superficial and the deep layers of the DL [12], separated by a narrow band of fatty tissue [13], which is an anatomical background of the MRI image of the DL. Individual parts comprising the DL layers are anatomically continuous, indicating a tendency to merge into larger anatomical and functional structures. Disruption of the DL occurs in supination external rotation and pronation external rotation [21], which is a similar pattern to FR injury [2]. There are no reliable epidemiological data on the frequency of injury to the medial ankle structures. About one-third of acute superficial DL injuries are concomitant with an FR tear [23]. The tear may progress deeply to the fibro-osseous tunnel causing injury to the FFS [2], the connection between which was shown in our study. Only case reports regarding SL or FR injury can be found in the literature, because injuries to the medial ankle ligaments are less common than to the lateral ligaments [24; 25; 26; 27]. SL tears are often associated with tibialis posterior tendon injuries [28], which may confirm the connections between them. Injuries to the medial structures of the ankle joint more often occur due to high energy traumas. This is probably because the medial ligaments are more robust and more resistant to minor injuries than the lateral ankle ligaments [29]. The presence of connections is also relevant in non-traumatic cases. Valgus hindfoot causes overloading of the posterior tibial tendon and the medial structures [30], causing dysfunction and aggravation of deformation, resulting in a flat foot [31; 32]. Malfunction of one structure causes the worse function of the other, resembling a domino effect. It can also be partly explained by the presence of the connections shown by us. Since the ankle joint is a functional unit, changes in the hindfoot are also manifested on the joint's lateral side, e.g., by the more horizontally running calcaneofibular ligament. This could be a reliable MRI symptom of the presence of hindfoot [33]. The accessory navicular bone prevalence is estimated to be between 4 to 25% [34; 35]. The incidence of the accessory navicular bone in the current study fits into the mentioned range. An overrepresentation of accessory navicular bone in patients with tibialis posterior tendon insufficiency can be noticed [34].