The interosseous membrane is in continuity with the apex of the interosseous ligament (Fig. 4.7). The anterior fibers are oblique, directed downward and laterally, whereas the posterior fibers are nearly vertical.

The anterior talofibular ligament (Figs. 4.8 and 4.9) is a flat, quadrilateral, relatively strong ligament measuring approximately 15 mm × 8 mm × 2 mm, 20 mm × 6 mm × 2 mm,⁴ or 12 mm × 5 mm × 2 mm.⁵ This ligament is formed by two distinct bands separated by an interval that allows the penetration of vascular branches. The upper band is larger than the lower. A third band occasionally may be present. The ligament originates from the inferior oblique segment of the anterior border of the lateral malleolus. The upper band reaches the origin of the anterior tibiofibular ligament and the lower band that of the calcaneofibular ligament; in many specimens, these two ligaments are united with arciform fibers at their malleolar origin. The anterior talofibular ligament courses anteromedially and inserts not on the talar neck but on the talar body just anterior to the lateral malleolar articular surface. Two flat tubercles are occasionally seen, corresponding to the insertion of the two bands. The anterior talofibular ligament is in close connection to the capsule of the talofibular joint. In the neutral position of the talus, the ligament is horizontal. In dorsiflexion, the ligament is directed slightly upward. In plantar flexion, the ligament firmly braces the talar body as it stretches over the nearly right angle formed by the union of the anterior and lateral surfaces of the talar body (Fig. 4.10); in this position, the ligament is directed downward, medially, and anteriorly.

Milner and Soames⁶ investigated the anatomical variations of the anterior talofibular ligament (ATFL) in 26 ankle specimens. They observed single, bifurcate, and trifurcate forms of the ATFL. The single form occurred in 38% (10 occurences with 8 bilateral and 2 unilateral), the bifurcate form in 50% (13 occurences with 12 bilateral and 1 unilateral), and the trifurcate form 12% (3 occurences with all unilateral). “The overall width of the ATFL did not appear to vary greatly irrespective of the number of bands present.”⁶ In a subsequent study based on the dissection of 40 ankles, the same authors⁷ provided the following mean measurements to the anterior talofibular ligament: length, 13 mm ± 3.9; width, 11 mm ± 3.3.

The calcaneofibular ligament (Figs. 4.8 and 4.11) is a strong cordlike or flat oval ligament and measures approximately 30 mm length, 5 mm width, and 3 mm thickness; or length of 20 mm with diameter of 4 mm to 8 mm⁴; or length of 30 mm to 40 mm with width of 4 mm to 5 mm.³ It originates from the lower segment of the anterior border of the lateral malleolus just below the origin of the inferior band of the anterior talofibular ligament. The origin does not extend to the tip of the lateral malleolus, which is left free. Near the origin, arciform fibers may unite the calcaneofibular ligament and the inferior band of the anterior talofibular ligament. With the foot in neutral position, the ligament courses posteriorly, inferiorly, and medially and is crossed superficially by the peronei tendons and their sheaths, which may leave an imprint on the ligament (Figs. 4.12 4.13, and 4.14). Only approximately 1 cm of the ligament remains uncovered by the crossing peronei.

The calcaneofibular ligament inserts on a small tubercle (tuberculum ligamenti calcaneo fibularis) located on the posterior aspect of the lateral calcaneal surface, posterosuperior to the peronei processus trochlearis. The insertion of the ligament is variable. Laidlaw, in a study of 750 calcanei, gives the following location of the calcaneal insertion of the ligament: typical location, 64.5%; anterior location, 25.5%; posterior location, 5.5%; downward location, 4.5%.⁸ The variable insertions result in variable obliquity of the ligament relative to the long axis of the fibula.

Ruth, in a study based on 30 dissected specimens and observations of 55 ankles during surgery, provides the following data with regard to the angle formed by the long axis of the calcaneofibular ligament and the long axis of the fibula (Fig. 4.15): 10 to 45 degrees, 74.66%; 0 degrees, 18.66%; 80 to 90 degrees, 4%; fan shaped, 2.66%.⁵ The valgus or varus position considerably affects the direction of and the angle formed by the calcaneofibular ligament. The obliquity of the ligament is increased with valgus of the heel and decreased with varus (Fig. 4.16). The obliquity of the ligament is also variable with the position of the ankle joint (Fig. 4.17). The calcaneofibular ligament crosses the talocalcaneal joint and is separated from it by the lateral talocalcaneal ligament. The interval between the two ligaments is filled with adipose tissue.

Trouilloud and colleagues⁹ reported on the variable relationship of the calcaneolibular ligament and the lateral talocalcaneal ligament in 26 ankles. They classified their findings into three categories: A, B, and C. In type A, 35%, the calcaneofibular ligament is reinforced by a lateral talocalcaneal ligament, attached to the former but diverging proximally or distally. In type B, 23%, a lateral talocalcaneal ligament exists anteriorly and independent of the calcaneofibular ligament. In type C, 42%, the lateral talocalcaneal ligament is absent and is replaced by an anterior talocalcaneal ligament, which is parallel now to the interosseous talocalcaneal ligament. In type C, the calcaneofibular ligament acquires more functional significance in providing stability to the subtalar joint.

Milner and Soames⁷ in a study based on the dissection of 40 ankles provided the following measurements in regard to the calcaneofibular ligament: length, 19.5 mm ± 3.9; width, 5.5 mm ± 1.6.

The posterior talofibular ligament (Figs. 4.8 and 4.18) is a very strong ligament situated in a nearly horizontal plane. Trapezoidal in contour, the ligament measures approximately 30 mm in posterior length, 5 mm in width at the fibular origin, and 5 mm to 8 mm in thickness. The ligament originates on the medial surface of the lateral malleolus from the lower segment of the digital fossa (Fig. 4.19). Thick and fasciculated, it courses horizontally toward the lateral and posterior aspects of the talus. The short transverse and intermediary fibers insert along the lateral surface of the talus in a groove along the posteroinferior border of the lateral malleolar articular surface up to its mid segment. The long fibers are directed posteromedially and insert on the posterior surface of the talus. The medial end expands and attaches on the posterolateral tubercle, the trigonal process, or the os trigonum (when present) and contributes to the formation of the floor of the flexor hallucis longus tunnel. When viewed posteriorly, the ligament is triangular, with a lateral apex and a medial base. The upper fibers of the posterior segment are in continuity medially with the superficial talotibial ligament, forming a posterior ligamentous sling.

Occasionally a band originates from the superior border of the posterior talofibular ligament near its origin, courses upward and medially, and inserts on the posterior tibial margin, blending with the fibers of the transverse component of the posterior tibiofibular ligament (Fig. 4.20); this insertion may reach the posterior surface of the medial malleolus. Paturet designates this ligament the posterior intermalleolar ligament.¹⁰ The posterior talofibular ligament is intracapsular but extrasynovial. The fibular origin is covered by the peronei retinaculum (Fig. 4.21). The superomedial segment is crossed by the tendon of the flexor hallucis longus (Fig. 4.22).

Milner and Soames⁷ in a study based on the dissection of 40 ankles provided the following measurements in regard to the posterior talofibular ligament: length, 23.0 mm ± 7.0; width, 5.5 mm ± 2.5.

The fibulotalocalcaneal ligament of Rouvière and Canela Lazaro (Figs. 4.23, 4.24, and 4.25) is an extrinsic ligament that occupies the posterolateral corner of the ankle and posterior subtalar joints. In 1924, Dujarier described briefly and produced a clear illustration of a posterior fibulocalcaneal ligament arising from the posterior aspect of the lateral malleolus and inserting on the posterosuperior aspect of the calcaneus laterally.¹¹ He qualified this ligament as being abnormal and mentioned that, in certain clubfeet, this ligament is considerably developed, forming the posterior fibulocalcaneal ligament of Bessel-Hagen (Fig. 4.26).

In 1932, Rouvière and Canela Lazaro, in a comprehensive study, described the peroneotalocalcaneal ligament.¹² This ligament is independent of the capsules and ligaments of the neighboring joints. It originates from the medial border of the peroneal groove located on the posterior border of the lateral malleolus, in common with the origin of the posterior tibiofibular ligament. Inferiorly, the origin may descend to the tip of the lateral malleolus and quite frequently may reach the origin of the calcaneofibular ligament.

At the origin, the peroneotalocalcaneal ligament is in close connection with the fibrous sheath of the peronei but soon separates from it and is directed downward, medially and posteriorly. This flat structure then divides into two fibrous laminae: superomedial and inferolateral. The superomedial lamina or talar component inserts on the posterolateral tubercle of the talus and contributes to the formation of the flexor hallucis longus fibrous tunnel. The inferolateral or peroneocalcaneal lamina is the major component of the ligament. It is directed downward and posteriorly, enlarges, and inserts nearly transversely on the entire width of the superior surface of the calcaneus. At times the calcaneal insertion is oblique, directed forward and medially. In approximately two thirds of the cases, the insertion remains localized to the superior surface of the calcaneus or reaches the lateral surface of the os calcis; the lateral border of the ligament is then separated by a small interval from the insertion of the calcaneofibular ligament. In the remaining one third, the calcaneal insertion clearly extends to the lateral calcaneal surface and blends with the insertion of the calcaneofibular ligament.

The frequency of occurrence of this ligament is 60% present as a well-defined ligament, 20% present as a thin, weak structure but with ligamentous texture, and 20% absent and replaced by a thin fascia.¹² Occasionally both components of the ligament are united, forming a continuous lamina.

On close analysis and as described by Rouvière and Canela Lazaro, the fibulotalocalcaneal ligament is the very thick inferior and suscalcaneal portion of the deep aponeurosis of the leg between the tunnel of the flexor hallucis longus and the tunnel of the peronei.¹² This ligament limits the dorsiflexion of the foot.

The tibioligamentous fascicle originates from the anterior segment of the anterior colliculus. The fibers present a gentle anterior concavity and insert on the superior border of the superomedial calcaneonavicular ligament. The anterior superficial tibiotalar fascicle, the tibionavicular fascicle, and the tibioligamentous fascicle constitute the broader but weaker component of the medial ligament (Fig. 4.36).

The tibiocalcaneal ligament (Fig. 4.37) is the strongest superficial component. It originates from the medial aspect of the anterior colliculus, descends vertically, and inserts on the medial border of the sustentaculum tali after interlacing its fibers with those of the superomedial calcaneonavicular ligament.¹⁴ This ligament is in continuity with the preceding tibioligamentous fascicle. In certain specimens, the origin of the latter overlaps the origin of the tibiocalcaneal ligament, and the interval is filled with adipose tissue. The tibiocalcaneal ligament measures approximately 1 cm in width at the origin and 1.5 cm at the insertion. The average length is 2 to 3 cm and the thickness 2 to 3 mm. It is a substantial structure.

The superficial posterior tibiotalar ligament originates from the posterior part of the medial surface of the anterior colliculus and the medial surface of the posterior colliculus (Fig. 4.38). The fibers are directed posteriorly, inferiorly, and laterally and insert on the posteromedial talar tubercle, reaching the flexor hallucis longus tunnel.³, ¹⁵, ¹⁶, ¹⁷, ¹⁸, ¹⁹ The posterior border of the tibiocalcaneal ligament is distinct from this ligament or the two may be in continuity; if they are in continuity, the superficial layer is represented as a large, fibrous, fan-shaped lamina deserving the “deltoid” denomination. The superficial posterior tibiotalar ligament is separated from the underlying posterior deep tibiotalar ligament with adipose tissue (more so anteriorly) and is in continuity along its superolateral border with the posterior talotibial capsule and the posterior talofibular ligament. The occasional absence of this ligament or its fusion to the deep talotibial ligament accounts for some of the variations in description.

The deep layer of the deltoid ligament (see Fig. 4.38) is short and strong. It is formed by a small anterior and a very strong posterior component.⁹, ¹⁶, ¹⁸, ¹⁹