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ankle. The front and back of the distal end of the bone are crossed by tendons, which mask to a certain extent its form.
Ossification. The body begins to ossify early in the second month of intra-uterine life. At birth it is well formed, and capped proximally and distally by pieces of cartilage,
Fuses with shaft about 20-24 years
in the proximal of which the centre
Appears early in 2nd month of foetal life
Appears before birth
Appears about 14 years
Fuses about 18th year
About 16 years.
The fibula is a slender bone with two enlarged ends. It lies to the lateral side of the tibia, with which it is firmly united by ligaments, and nearly equals that bone in length.
The first difficulty which the student has to overcome is to determine which is the proximal and which the distal extremity of the bone. This can easily be done by recognising the fact that there is a deep pit on the medial aspect of the distal extremity immediately behind the triangular articular surface. Holding the bone vertically with the distal extremity downwards and so turned that the triangular articular area lies in front of the notch already spoken of, the subcutaneous non-articular aspect of the distal extremity will point to the side to which the bone belongs
The proximal extremity or head of the fibula (capitulum fibula), of irregular rounded form, is bevelled on its medial surface so as to adapt it to the form of the distal surface of the lateral condyle of the tibia. At the border where this surface becomes confluent with the lateral aspect of the head there is a pointed upstanding eminence called the apex capituli fibula; to this the short fibular collateral ligament is attached, as well as a piece of the tendon of the biceps, which is inserted into its anterior part. Immediately to the medial side of this, and occupying the summit of the medial sloping surface, there is an articular area (facies articularis capituli), of variable size and more or less triangular shape. This area articulates with the lateral condyle of the tibia. The long fibular collateral ligament, together with the remainder of the tendon of the biceps muscle which surrounds it, is attached to the lateral and proximal side of the head in front of the apex capituli. On the front and the back of the head there are usually prominent tubercles. The anterior of these is associated with the origin of the peronæus longus muscle; the posterior furnishes an origin for the proximal fibres of the soleus, and serves to deepen the groove, behind the proximal tibio-fibular joint, in which the tendon and fleshy part of the popliteus muscle play.
The constricted portion of the body distal to the head is often referred to as the neck; around the lateral side of this the common peroneal nerve winds.
The body of the fibula (corpus fibula) presents many varieties in the details of its shape and form, being ridged and channelled in such a way as greatly to increase the difficulties of the student in recognising the various surfaces
described. It is described as possessing three surfaces, named. the lateral, the medial, and the posterior. The surfaces are separated from one another by three borders or crests, named medial, lateral, and anterior; and, in addition, the medial surface is traversed longitudinally by a ridge called the interosseous crest, which divides it into an anterior and a posterior part. The most important point is first to determine the position of the
GROOVE FOR TENDON
OF TIBIALIS POS
TERIOR AND FLEXOR
GROOVE FOR, FLEXOR HALLUCIS
FIG. 250.-THE RIGHT TIBIA AND FIBULA SEEN FROM
The Posterior surface of the fibula is coloured red; the
lateral surface is left uncoloured.
FACET FOR TIBIA.
NUTRIENT FORAMEN (in this case directed proximally)
FACET FOR TALUS
The lateral surface, which is separated from the medial surface by the anterior crest, is often hollowed out in its middle part, and it is twisted, so that its proximal part is directed somewhat forwards, while its distal part turns backwards and becomes continuous distally with the broad, shallow groove which occupies the posterior surface of the lateral malleolus. The lateral surface is limited posteriorly and separated from the posterior surface of the body by the lateral crest, which is usually sharp and well defined except at its extremities, where it tends to become smooth and rounded. Its proximal end joins the head distal to and in front of the apex capituli, and terminates distally at a point just proximal to the pit on the medial surface of the distal extremity. In its proximal third or The anterior part of the medial fourth the lateral crest is often rough where fibres of
surface is coloured blue; the
posterior part of the medial the soleus muscle arise from it.
face is coloured red.
anterior crest. If the bone is held in the position which it normally occupies in the leg, it will be noticed that the lateral surface of the distal extremity is limited in front and behind by two lines, which converge and enclose between them a triangular subcutaneous area which lies immediately proximal to the lateral malleolus. From the summit of the triangle so formed a welldefined ridge may be traced along the front of the body to reach the anterior aspect of the head. This is the anterior crest.
FIG. 252.-RIGHT FIBULA AS
The interosseous crest, so named because the interosseous membrane is attached to it, is the ridge which lies just medial to the anterior crest, or towards the tibial side on the anterior aspect of the bone. It is not so prominent as the anterior crest, and it extends from the neck of the bone to the apex of a rough triangular impression that lies proximal to the articular surface on the medial aspect of the distal end. The interval between the anterior and interosseous crests is the anterior part of the medial surface. This interval is, as a rule, of considerable width in the distal half of the bone, but the two crests tend to run much closer together proximally; indeed, it is not uncommon to find that they coalesce to form a single crest.
The posterior part of the medial surface is the elongated area behind the proximal three-fourths or four-fifths of the interosseous crest. It is limited posteriorly by the medial crest, a sharp, salient ridge, which commences at the medial margin of the posterior aspect of the head, but does not reach the distal end of the bone; for the distal end of the medial crest curves forwards and joins the interosseous crest about three or four inches from the distal extremity of the body; therefore, the posterior part of the medial surface is not represented in the distal part of the body. On the proximal third of this surface there is frequently found an oblique ridge which begins near the interosseous crest at the level of the neck and extends distally and backwards to join the medial crest. When the proximal part of the medial crest is indistinct this ridge may be mistaken for it.
The posterior surface forms the remainder of the
body. It is the district bounded laterally by the lateral crest and medially by the medial crest and the distal fourth or fifth of the interosseous crest. It is twisted in the same degree as the lateral surface; and, therefore, while its proximal part is directed backwards, its distal part is directed medially and is in line with the medial surface of the malleolus. The nutrient foramen is situated on the posterior surface, at or near the middle of the body near the medial crest, and is directed towards the distal end of the bone.
The anterior crest gives attachment to the anterior intermuscular septum, and, at its distal end, to the ligamentum transversum cruris, while the posterior intermuscular septum is attached to the lateral crest. These septa enclose the peroneus longus and brevis muscles, which arise from the lateral or peroneal surface, and separate them from the muscles on the front and the back of the leg. The interosseous membrane is attached to the whole length of the interosseous crest. The anterior part of the medial surface provides origin for the extensor halluciis, the extensor digitorum longus and the peroneus tertius; while the tibialis posterior arises from the posterior part of the medial surface. The medial crest is the fibular attachment of a strong sheet of fascia which covers the tibialis posterior, and separates it from the flexors of the toes. The soleus muscle arises from the proximal third of the posterior surface, while the flexor hallucis longus takes origin from its distal two-thirds.
The distal extremity of the fibula, or lateral malleolus, is of pyramidal form. Its medial surface is furnished with a triangular articular area (facies articularis malleoli), plane from before backwards, and slightly convex proximodistally, which articulates with a corresponding surface on the lateral side of the body of the talus. Behind this there is a deep pit, to which the posterior talo-fibular ligament is attached. Proximal to the articular facet there is a rough triangular area, from the summit of which the interosseous crest arises; to this are attached the strong fibres of the distal interosseous ligament which binds together the opposed surfaces of the tibia and fibula. The lateral surface of the distal extremity forms the elevation of the lateral malleolus which determines the shape of the projection of the lateral ankle. Rounded from side to side and proximodistally, it terminates in a pointed process, which reaches a more distal level than the corresponding process of the tibia, from which it also differs in being narrower and more pointed and being placed in a plane nearer the heel. Proximally, this surface, which is subcutaneous, is continuous with the triangular subcutaneous area so clearly defined by the convergence of the lines which unite to form the anterior crest. The anterior border and tip of the lateral malleolus furnish attachments to the anterior talo-fibular and calcaneo - fibular ligaments. The posterior surface of the lateral malleolus, broad proximally, where it is confluent with the lateral or peroneal surface, is reduced in width distally by the presence of the pit which lies to its medial side. This aspect of the bone is grooved (sulcus malleolaris) by the tendons of the peronæus longus and brevis muscles, which curve round the posterior and distal aspects of the malleolus.
The proportionate length of the fibula to the body height is as 1 is to 4:37-4·82.
Arterial Foramina.-Numerous minute vascular canals are seen piercing the lateral surface of the head, and one or two of larger size are seen on the medial surface immediately anterior to the proximal articular facet. The canal for the nutrient artery of the body, which has a distal direction, is situated on the posterior surface of the bone about its middle. The lateral surface of the lateral malleolus displays the openings of many small canals, and one or two larger openings are to be noted at the bottom of the pit behind the distal articular surface.
Connexions. The head and lateral malleolus, and part of the body immediately proximal to the latter, are subcutaneous. The remainder of the body is covered on all sides by the muscles which surround it. Proximally the bone plays no part in the formation of the knee-joint, but distally it assists materially in strengthening the ankle-joint by its union with the tibia and its articulation with the talus. In position the bone is not parallel to the axis of the tibia, but oblique to it, its proximal extremity lying posterior and lateral to a vertical line passing through the lateral malleolus.
Ossification. The body begins to ossify about the middle of the second month of fœtal life. At the end of the third month there is but little difference in size between it and the tibia, and at birth the fibula is much larger in proportion to the size of the
tibia than in the adult. Its extremities are cartilaginous, the distal extremity not being as long as the medial malleolar cartilage of the tibia. It is in this, however, that an ossific centre first appears about the end of the second year, which increases rapidly in size, and unites with the body in about nineteen years. The centre for the proximal epiphysis begins to ossify about the third or fourth year, and union with the body is not complete until a period somewhat later than that for the distal epiphysis. The mode of ossification of the distal extremity is an exception to the general rule that epiphyses which are the first to ossify are the last to unite with the body. This may possibly be accounted for by the fact that the distal end is functionally more important than the rudimentary proximal end, since in man alone, of all vertebrates, does the lateral malleolus reach beyond the level of the medial malleolus. Its early union with the body is doubtless required to ensure the stability of the ankle-joint necessitated by the assumption of the erect position.
Appears about middle of 2nd month of foetal life
Fuses with shaft
about 20-24 years
Fuses with shaft about 19 years About About 12 years. 16 years. FIG. 253.-OSSIFICATION OF FIBULA.
In its earlier stages of development it has been stated, on the authority of Leboucq, Gegenbaur, and others, that the fibula as well as the tibia is in contact with the femur. This is, however, denied by Grunbaum ("Proc. Anat. Soc.," Journ. Anat. and Physiol., vol. xxvi. p. 22), who states that after the sixth week the fibula is not in contact with the femur, and that prior to that date it is impossible to differentiate the tissue which is to form femur from that which forms fibula.
BONES OF THE FOOT.
The bones of the foot, twenty-six in number, are arranged in three groups: the tarsal, seven in number; the metatarsal, five in number; the phalanges, fourteen in number. Comparing the foot with the hand, the student will be struck with the great proportionate size of the tarsus, as compared with the carpus, and the reduction in size of the bones of the toes as compared with the fingers. The size of the metatarsal segment more nearly equals that of the metacarpus.
The tarsus consists of seven bones (ossa tarsi) the talus or astragalus, calcaneus, navicular or scaphoid, three cuneiforms, and the cuboid. Of irregular form and varying size, they may be described as roughly cubical, presenting for examination dorsal and plantar surfaces, as well as anterior, posterior, medial, and lateral aspects.
The talus (O.T. astragalus) is the bone through which the body weight is transmitted from the leg to the foot. Proximally the tibia rests upon it, whilst on either side it articulates with the medial and lateral malleolar processes of the tibia and fibula respectively; inferiorly it overlies the calcaneus, and anteriorly it articulates with the navicular. For descriptive purposes the bone is divisible into three parts-the corpus tali (body) blended in front with the collum tali (neck), which supports the caput tali (head).
The dorsal surface of the body is provided with a saddle-shaped articular surface (trochlea tali), broader in front than behind, for articulation with the distal surface of the tibia. The medial edge of the trochlea is straight; whilst the lateral border, which is sharp in front and more rounded behind, is curved medially posteriorly, where it is bevelled to form a narrow, elongated, triangular facet, which is in contact with the transverse or distal tibio-fibular ligament during flexion of the ankle. (Fawcett, Ed. Med. Journ., 1895.) Over the lateral border the cartilagecovered surface is continuous laterally with an extensive area of the form of a quadrant. This is concave from above downwards, and articulates with the medial