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Lig. Capituli Fibula Anterius.-The anterior ligament of the head of the fibula (Fig. 317) is a strong flat band whose fibres extend from the anterior aspect of the fibular head, proximally and medially, to the adjoining part of the lateral condyle of the tibia.
Lig. Capituli Fibula Posterius.-The posterior ligament of the head of the fibula (Fig. 319) is a similar, but weaker band, passing, proximally and medially, from the posterior aspect of the fibular head to the posterior aspect of the lateral condyle of the tibia, where it is attached immediately distal to the opening in the capsule of the knee-joint, from which the tendon of the popliteus muscle escapes. Equally strong but much shorter bands are found on the lateral and medial aspects of the joint. The former is intimately associated with the tendon of the
FIG. 321. ANKLE-JOINT DISSECTED FROM BEHIND WITH PART OF THE ARTICULAR CAPSULE REMOVED.
biceps flexor cruris muscle which strengthens the lateral aspect of the joint, and here also is found the occasional opening by which it communicates with the kneejoint.
The synovial stratum is in certain cases continuous with that of the kneejoint in the manner already described.
Membrana Interossea Cruris.-The interosseous membrane (Figs. 317 and 321) plays the part of an accessory ligament both for the proximal and the distal tibiofibular joints. It is attached to the interosseous borders on the shafts of the tibia and fibula, and binds them together. The general direction of its fibres is from the tibia distally and laterally to the fibula, but many fibres pass in the opposite direction. The membrane may extend upwards until it comes into contact with the ligaments of the proximal tibio-fibular joint, but there is always a vertical oval aperture in its proximal part for the forward passage of the anterior tibial vessels.
This aperture (Fig. 317), which is about one inch long, adjoins the shaft of the fibula at a point rather less than one inch distal to its head. Towards the distal end of the leg the distance between the tibia and the fibula rapidly diminishes, and consequently the width of the interosseous membrane is correspondingly reduced, and it is tense throughout its entire length. In the distal part of the membrane there is a small opening for the passage of the perforating peroneal vessels. There is no sharply marked demarcation between the interosseous membrane and the interosseous ligament which connects the distal ends of the tibia and fibula-the one, indeed, may be said to run into the other.
Syndesmosis Tibiofibularis.-The distal tibio-fibular joint is not on all occasions provided with articular cartilage, so that it may either be a separate articulation, or it may merely present a series of ligaments which are accessory to the (ankle-joint), because it is clear that, under any circumstances, the object aimed at in this articulation is to obtain additional security for the ankle-joint. The articular surface on the tibia, when present, constitutes a narrow articular strip on the lateral side of the distal end of the bone, and the joint-cavity is practically an upward extension of the ankle-joint. The corresponding fibular facet is continuous with the extensive articular area, by means of which the fibula articulates with the talus. By far the greater part of the opposing surfaces of tibia and fibula are, however, non-articular and rough.
The supporting ligaments are of great strength.
Lig. Malleoli Lateralis Anterius.-The anterior ligament of the lateral malleolus (O.T. anterior inferior tibio-fibular ligament) (Fig. 322) consists of strong fibres which pass obliquely distally and laterally from the front of the distal end of the tibia to the front of the lateral malleolus.
Lig. Malleoli Lateralis Posterius.-The posterior ligament of the lateral malleolus (O.T. posterior inferior tibio-fibular ligament) (Figs. 321 and 322) is equally strong, and passes in a similar direction between corresponding posterior surfaces.
Lig. Malleoli Lateralis Distale.-The distal ligament of the lateral malleolus (O.T. transverse inferior tibio-fibular ligament) (Figs. 321 and 322) stretches between the posterior border of the distal end of the tibia and the proximal end of the pit on the medial and posterior aspect of the lateral malleolus.
Ligamentum Interosseum.-An interosseous ligament, powerful and somewhat extensive, connects the contiguous rough non-articular surfaces. Proximally, as already mentioned, it is continuous with the interosseous membrane. Anteriorly and posteriorly it comes into contact with the more superficial ligaments. Distally it descends until it comes into intimate association with the articular cavity.
A synovial stratum is found lining the small articular cavity, but it is always a direct prolongation from that which lines the ankle-joint.
The ankle-joint is a ginglymus variety of a diarthrosis. The bones which enter into its formation are the distal ends of the tibia and fibula, with the articular areas on the superior, lateral, and medial surfaces of the talus. The tibia and fibula, aided by the distal ligament of the lateral malleolus, form a three-sided socket within which the talus is accommodated. The roof or most proximal part of the socket, which is wider in front than behind, is formed, chiefly, by the quadrilateral articular surface on the distal end of the tibia, but towards its posterolateral margin the distal ligament of the lateral malleolus assists in its formation. There also the tibial articular surface is continuous with the narrow articular facet already described as forming part of the tibio-fibular syndesmosis. The medial wall of the socket is formed by the articular facet on the lateral side of the medial malleolus, and there is no interruption of the articular cartilage between the roof and medial wall. The lateral wall of the socket is quite separate from the foregoing parts, and consists of a large triangular facet upon the medial side
of the lateral malleolus. This facet is situated immediately in front of the deep pit which characterises the posterior part of this surface of the fibula.
A small lunated facet is frequently found upon the anterior surface of the distal end of the tibia, particularly among those races characterised by the adoption of the "squatting" posture. When this facet exists it is continuous with the anterior margin of the roof of the socket, and it articulates with a similar facet upon the superior surface of the neck of the talus in the extreme flexion of the ankle-joint which "squatting" entails.
The articular surface upon the body of the talus adapts itself to the tibiofibular socket, and presents articular facets corresponding to the roof and sides of the socket. Thus the superior surface of the talus possesses a quadrilateral articular area, wider in front than behind, distinctly convex in the antero-posterior direction, and slightly concave transversely. In addition, towards its posterolateral margin, there is also a narrow antero-posterior facet corresponding to the distal ligament of the lateral malleolus. The articular cartilage of this superior surface is continued without interruption to the tibial and fibular sides of the bone, although the margins of the superior area are sharply defined from the facets on
the sides, the lateral of which is triangular in outline, while the medial is piriform, but in each case the surface is vertical.
Ligaments. The ligaments form a complete investment for the joint, i.e. a fibrous stratum of an articular capsule in which the individual parts vary considerably in strength, and are described under Their separate names. proximal attachments are
restricted to the epiphyses of the distal ends of the tibia and fibula, and the epiphyseal lines are therefore extra-capsular.
The anterior ligament is an extremely thin membrane, containing very few longitudinal fibres. It extends from the distal border of the tibia to the dorsal border of the head of the talus, passing in front of a pad of fat which fills up the hollow above the neck of that bone.
The posterior ligament is attached to contiguous non-articular borders of the tibia and talus. Many of its fibres radiate medially from the lateral malleolus. This aspect of the joint is strengthened by the strong, well-defined, distal ligament of the lateral malleolus already described in connexion with the tibio-fibular syndesmosis.
The lateral ligament (Figs. 321, 322, and 324) is very powerful, and is divisible into three fasciculi, which are distinguished from each other by names, descriptive of their chief points of attachment.
Lig. Talofibulare Anterius.-The anterior fasciculus is the shortest. extends from the anterior border of the lateral malleolus to the talus immediately in front of its lateral articular surface.
Lig. Calcaneofibulare. The middle fasciculus is a strong and rounded cord. It is attached by one end to the front of the tip of the lateral malleolus, and by the other to the lateral side of the calcaneus immediately proximal and posterior to the groove for the peroneal tendons.
Lig. Talofibulare Posterius. The posterior fasciculus is the strongest. It runs transversely between the distal part of the fossa on the medial aspect of the fibular malleolus and the posterior surface of the talus, where it is attached to the posterior process and the adjoining rough surface. Sometimes this process is detached from the talus, and represents a separate bone-the os trigonum.
Lig. Deltoideum.-The deltoid ligament is the medial ligament of the ankle-joint (Figs. 322 and 323). It has the general shape of a delta, and is even stronger
1st cuneiform and 1st metatarsal
than the lateral ligament. It is attached proximally to a marked impression on the distal part of the medial malleolus, and below, in a continuous layer, to the navicular, talus and calcaneus. In it we may recognise the following special bands (a) the lig. talotibiale anterius, which extends from the front of the medial malleolus to the neck of the talus; (b) the lig. talotibiale posterius, stretching between the back of the medial malleolus and the postero-medial rough surface of the talus; (c) the lig. tibionaviculare, which extends from the tip of the medial malleolus to the medial side of the navicular body; (d) the lig. calcaneotibiale, which extends between the tip of the medial malleolus and the medial side of the sustentaculum tali; (e) lig. talotibiale profundum, which consists of deeper fibres extending from the tip of the medial malleolus to the medial side of the talus. A synovial stratum lines the fibrous stratum of the articular capsule and, as
FIG. 323. ANKLE AND TARSAL-JOINTS FROM THE TIBIAL ASPECT.
already described, the articular cavity extends into the interval between the tibia and fibula distal to the tibio-fibular interosseous ligament. Both at the front and back of the ankle-joint, as well as proximally in the angle formed by the three bones, the synovial membrane covers pads of fat.
Movements at the Ankle-Joint.-In the erect attitude the foot is placed at right angles to the leg; in other words, the normal position of the ankle-joint is flexion. Those movements which tend to diminish the angle so formed by the dorsum of the foot and the front of the leg are called dorsiflexion, while those which tend to increase the angle, i.e. to straighten the foot upon the leg, are called extension. As a matter of fact neither dorsiflexion nor extension is ever completely carried out, and the range of movement of which the foot is capable is limited to about 90°. These movements occur about an obliquely transverse axis, as is indicated by the natural lateral pointing of the toes. The weight of the body falls slightly anterior to the anklejoint, so that a certain amount of muscular action is necessitated in order to maintain the foot at right angles to the leg; but additional stability is obtained from the obliquity above mentioned. When the foot is raised from the ground, muscular action tends naturally to produce a certain amount of extension. When the foot is extended, as in standing on the toes, the posterior narrow part of the talus moves forwards into the wider part of the interval between the tibia and fibula, whereas in dorsiflexion, as in raising the anterior part of the foot from the ground, the widest part of the talus is forced back between the tibia and fibula; but notwithstanding the difference between these two movements, the fibula remains in close contact with the talus by reason of the action of the ligamentum malleoli lateralis distale and the posterior talo-fibular ligament, so that lateral movement is prevented.
It is doubtful whether lateral movement at the ankle-joint can be obtained by any natural movement of the foot, although it is generally believed that in the position of partial extension a small amount of side-to-side movement may be produced by the application of external force. "This apparent play" of the ankle-joint during extension is really due to oscillation of the small bones of the foot on each other, largely of the navicular on the talus, but also of the cuboid on the calcaneus. Excessive mobility of these latter is restrained by an important function of the posterior tubercle of the cuboid which locks into a notch in the calcaneus (Blake).
The intertarsal joints are all diarthroses in which the gliding movement is characteristic, as in the carpus. With the view of obtaining a proper conception of the many beautiful mechanical principles involved in the construction of the foot, it is necessary to study these articulations with considerable attention to detail.
FIG. 324.-LIGAMENTS ON THE LATERAL ASPECT OF THE ANKLE-JOINT AND ON THE DORSUM OF THE TARSUS.
Articulatio Talocalcanea. The talus and calcaneus articulate with each other in the talo-calcaneal joint.
This joint is situated between the inferior facet on the body of the talus and a corresponding facet on the superior aspect of the posterior part of the calcaneus. On each bone the articulation is limited in front by a wide, deep groove which runs obliquely across each bone from the medial to the lateral side and forwards.
The supporting and investing ligaments form the fibrous stratum of an articular capsule, consisting for the most part of short fibres, but the joint derives additional strength from the calcaneo-fibular ligaments of the ankle-joint. The fibrous stratum of the capsule is subdivided into the following talo-calcaneal bands:
The ligamentum talocalcaneum anterius consists of a band of short fibres placed immediately in relation to the anterior end of the deep groove which bounds the articular facets. They are attached to the antero-lateral aspect of the neck of the talus, from which they extend downwards to the adjacent superior surface of the calcaneus.
The ligamentum talocalcaneum laterale (Fig. 324) is in continuity with the posterior border of the preceding ligament, and it is placed parallel to, but on