*1.2.1 Bony structure*

The ankle joint consists of the ankle mortise and talus. The tibial plafond forms the ankle mortise, together with the distal fibula through syndesmosis ligaments. The width of the talar dome is wider in the anterior aspect. Hence, the ankle joint is more stable in dorsiflexion position than in plantarflexion.

If the ATFL does not heal well after rupture, its laxity will result in excessive plantarflexion and supination of the ankle, which decreases the stability of the joint, increases the compensative burden of peroneal muscles, and increases the wearing of articular cartilage. Even after healing, some patients may still have lateral ankle pain and swelling despite their return of full pre-injury activity. The presence of local painful scarring, synovitis, post-traumatic weakness of peroneal muscles, and injury to the proprioception afferent fibers inside the ATFL may be the causative

The deltoid ligament is composed of a superficial layer and a deep layer. The superficial layer, which is positioned across the ankle and subtalar joint, consists of

The deltoid ligament complex is composed of the deltoid ligament and the spring ligament (the calcaneonavicular ligament). The spring ligament helps not only to maintain the supination of midfoot but also to support the medial ankle structure through its connection with the deltoid ligament by the tibiospring ligament. A patient with MAI often presented with dysfunction of these two structures.

The peroneal musculature is the dynamic stabilizer of the lateral ankle joint. Lateral ankle sprains may cause injury to the ATFL as well as to the peroneal muscles. Not only can the muscular fibers be injured, the neuromuscular function can also be affected. It has been reported that the reaction time of the peroneal muscles may be delayed in patients with a history of repeated sprains, which may increase the risk of another lateral ankle sprain when the ankle lands in a supinated position [21]. This delay may be related to the deafferentation of receptors in the muscle tendon and ligaments around the ankle joint after a sprain injury [22]. Proprioception deficits are frequently encountered in patients with CAI. The dysfunction of proprioception will result in poor joint position sense, which means

*Superficial and deep layers of deltoid ligament. (a) Superficial deltoid ligament. (1) Tibionavicular ligament, (2) tibiospring ligament, (3) tibiocalcaneal ligament, (4) deep posterior tibiotalar ligament, (5) spring ligament complex (plantar and superomedial calcaneonavicular ligaments), (6) anterior colliculus, (7) posterior colliculus, (8) intercollicular groove, (9) sustentaculum tali, (10) medial talar process, (11) lateral talar process, (12) navicular, (13) navicular tuberosity. (b) Deep deltoid ligament. (1) Tibionavicular ligament, (2) tibiospring ligament, (3) tibiocalcaneal ligament, (4) deep posterior tibiotalar ligament, (5) spring ligament complex (superomedial calcaneonavicular ligament), (6) medial talar process, (7) sustentaculum tali, (8) medial talocalcaneal ligament, (9) tibialis posterior tendon (from Vega et al. [68]).*

four components: the tibionavicular ligament, the tibiospring ligament, the tibiocalcaneal ligament, and the superficial posterior tibiotalar ligament [20]. The deep layer, which is thicker and positioned across the ankle joint only, consists of two components: the anterior tibiotalar ligament and the deep posterior tibiotalar

reasons of these residual symptoms.

*Diagnosis and Treatment of Chronic Ankle Instability DOI: http://dx.doi.org/10.5772/intechopen.89485*

ligament (**Figure 2**).

**Figure 2.**

**85**

*1.2.3 Neuromuscular structure*

The stability of ankle joint will be at risk if the mortise is relatively less constrained. A posteriorly positioned fibula, either congenital or post-traumatic, may increase the anterior opening of ankle mortise and cause instability [12, 13]. The length of the fibula does not affect the stability of the ankle [14]. A decreased talar dome coverage of the tibia plafond, evaluated from plain, weight-bearing, and lateral view radiographs as well as an increased lateral radius of the talus, is linked to the development of lateral ankle instability (LAI) [13, 15].

Medial ankle instability (MAI) is less discussed in the literature. It has been reported that during arthroscopic exploration for lateral ankle instability, 20% of patients show a concomitant injury of the deltoid [16]. MAI involves the dysfunction of the deltoid ligament complex, which may cause valgus deformity of the ankle, and, vice versa, hindfoot valgus deformity carries a higher risk of developing MAI.

#### *1.2.2 Ligamentous structure*

The lateral ankle ligaments comprise of the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL). The ATFL is taut when the ankle is in plantarflexion position, whereas the PTFL and CFL are taut when the ankle is in dorsiflexion position (**Figure 1**) [17].

Broström surgically opened 105 sprained ankles and reported ATFL injury in two-thirds and combined ATFL and CFL injuries in one-fourth of patients [18]. This finding suggested that the ATFL is the first-line structure against supination. The ATFL has two fascicles; the superior fascicle is positioned intra-articularly, which suggests a poor healing potential and becomes stretched in ankle plantarflexion. The inferior fascicle, on the other hand, is extra-articular and shares a common insertion with the CFL in the fibula and is not stretched in ankle plantarflexion [19].

#### **Figure 1.**

*Lateral view of the right ankle. The tension of the ATFL and CFL can be observed in different ankle positions: (a) dorsiflexion, (b) plantar flexion (with kind permission from Vega et al. [68]).*

### *Diagnosis and Treatment of Chronic Ankle Instability DOI: http://dx.doi.org/10.5772/intechopen.89485*

**1.2 Functional anatomy**

*Essentials in Hip and Ankle*

The ankle joint consists of the ankle mortise and talus. The tibial plafond forms the ankle mortise, together with the distal fibula through syndesmosis ligaments. The width of the talar dome is wider in the anterior aspect. Hence, the ankle joint is

The stability of ankle joint will be at risk if the mortise is relatively less constrained. A posteriorly positioned fibula, either congenital or post-traumatic, may increase the anterior opening of ankle mortise and cause instability [12, 13]. The length of the fibula does not affect the stability of the ankle [14]. A decreased talar dome coverage of the tibia plafond, evaluated from plain, weight-bearing, and lateral view radiographs as well as an increased lateral radius of the talus, is linked

Medial ankle instability (MAI) is less discussed in the literature. It has been reported that during arthroscopic exploration for lateral ankle instability, 20% of patients show a concomitant injury of the deltoid [16]. MAI involves the dysfunction of the deltoid ligament complex, which may cause valgus deformity of the ankle, and, vice versa, hindfoot valgus deformity carries a higher risk of

The lateral ankle ligaments comprise of the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL). The ATFL is taut when the ankle is in plantarflexion position, whereas the PTFL and CFL are taut when the ankle is in dorsiflexion position (**Figure 1**) [17]. Broström surgically opened 105 sprained ankles and reported ATFL injury in two-thirds and combined ATFL and CFL injuries in one-fourth of patients [18]. This finding suggested that the ATFL is the first-line structure against supination. The ATFL has two fascicles; the superior fascicle is positioned intra-articularly,

which suggests a poor healing potential and becomes stretched in ankle

a common insertion with the CFL in the fibula and is not stretched in ankle

plantarflexion. The inferior fascicle, on the other hand, is extra-articular and shares

*Lateral view of the right ankle. The tension of the ATFL and CFL can be observed in different ankle positions:*

*(a) dorsiflexion, (b) plantar flexion (with kind permission from Vega et al. [68]).*

more stable in dorsiflexion position than in plantarflexion.

to the development of lateral ankle instability (LAI) [13, 15].

*1.2.1 Bony structure*

developing MAI.

plantarflexion [19].

**Figure 1.**

**84**

*1.2.2 Ligamentous structure*

If the ATFL does not heal well after rupture, its laxity will result in excessive plantarflexion and supination of the ankle, which decreases the stability of the joint, increases the compensative burden of peroneal muscles, and increases the wearing of articular cartilage. Even after healing, some patients may still have lateral ankle pain and swelling despite their return of full pre-injury activity. The presence of local painful scarring, synovitis, post-traumatic weakness of peroneal muscles, and injury to the proprioception afferent fibers inside the ATFL may be the causative reasons of these residual symptoms.

The deltoid ligament is composed of a superficial layer and a deep layer. The superficial layer, which is positioned across the ankle and subtalar joint, consists of four components: the tibionavicular ligament, the tibiospring ligament, the tibiocalcaneal ligament, and the superficial posterior tibiotalar ligament [20]. The deep layer, which is thicker and positioned across the ankle joint only, consists of two components: the anterior tibiotalar ligament and the deep posterior tibiotalar ligament (**Figure 2**).

The deltoid ligament complex is composed of the deltoid ligament and the spring ligament (the calcaneonavicular ligament). The spring ligament helps not only to maintain the supination of midfoot but also to support the medial ankle structure through its connection with the deltoid ligament by the tibiospring ligament. A patient with MAI often presented with dysfunction of these two structures.
