The direction of the clavicle is nearly horizontal; sometimes its external end drops, as in women from whom the shoulders are falling; more often it is raised a little above the horizontal, as it is seen on some very muscular individuals. Horizontal, or nearly horizontal, in the transverse direction, the clavicle is very obliquely directed frontward to backward and inward to outward. Its internal or anterior extremity is supported by the sternocostal notch: the external or posterior one is supported by the acromion. Thus thrown as a bridge or a flying buttress from the sternum to the stub of the shoulder, the clavicle draws under the skin the lengthened bulge of its upper surface, while by its under surface it comes in relation successively from inward to outward with the first rib, the first intercostal space, the second rib and the coracoid process; usually it remains at distance from these parts but it can also go in contact with some of them (1st rib, coracoid process) - here lie the variations into the details of its osteology.
The left clavicle (superior surface).
The clavicle is a bone of elongated shape, difficult to define, it varies on the various points of extended from the bone definitely flattened from top to bottom in its external part, the clavicle swells to become prismatic and triangular in its internal half.
The clavicle can be described two surfaces, two borders and two ends. To find and follow the surfaces and the borders, it is necessary to leave the external end of the bone where this division in two faces is well accentuated.
Put on the top the smoothest surface, outwards the flattened end, and ahead the concave border of this end; to give the direction indicated higher and represented on our illustrations.
Body of the clavicle
The upper surface of the clavicle (cervical)
Large, flattened and a little rough, in the external third of the bone, this surface becomes narrow, smooth and convex frontward to backward in its internal two thirds. Its middle part, smooth, matches the platysma muscle and the skin. Its ends carry the print of the muscles to which they give insertion middleward, towards the sternal end, two light series of roughnesses, hardly visible, outwards mark the clavicular insertion of the sternocleidomastoid muscle, towards the acromial end, along the former edge, the broad rough notch from 3 to 6 millimeters which matches the clavicular insertion of the deltoid can be seen; behind this one, towards the posterior edge, of the parallel rough scratches mark clavicular insertion of the trapezoid muscle.
The under surface of the clavicle (costal or thoracic)
Large outwards, narrow inward, the under surface of the clavicle is dug in its middle part by a gutter lengthened along the main stream of the bone, the gutter of the subclavius muscle. The depth of this gutter, in connection with the development of the muscle which fits there, is very variable: sometimes it is hardly indicated, as on certain round female clavicles its former lip is in general rather clear, the posterior one merges imperceptibly with the posterior border of the bone.
The left clavicle (inferior surface).
The nutrient foramen is usually in the gutter, towards the posterior lip, it gets in very obliquely towards the external end of the bone; sometimes there are two of them.
Inside the subclavian gutter, towards the sternal end of the bone, the lower face of the clavicle presents the print of the costoclavicular ligament. This print offers variable aspects sometimes and generally, it is a rough eminence, oval, salient contour; other times, it is a small oval cavity; on some clavicles finally it is hardly marked; these differences in aspect are due to the unequal development of the ligament which fits there.
Outside the gutter, towards the acromial end of the bone, the under surface of the clavicle presents roughnesses always very marked; these roughnesses start behind, on the posterior edge of the bone, with a large conoide process, which gives insertion to the conoid ligament from there, they move outwards and ahead and take the aspect of a rough, large surface from 5 to 8 millimeters, presenting two or three very salient mamelons, separated by depressions this surface gives insertion to the trapezoidal ligament.
The anterior border of the clavicle
It is thin, concave, rough and slicing in its external third, where it gives insertion to the deltoid sometimes one of the roughnesses, the most internal, is much more salient than the others and is named the deltoideus process. It becomes convex, very broad and takes the aspect of a true surface in its internal two thirds, flattened and hammered by the insertion of the pectoralis major muscle.
The posterior border of the clavicle
Divided into two unequal parts by the always appreciable projection of the conoid process, it is thick, convex and rough in its external part, which gives insertion to the clavicular portion of the trapezoid muscle; it becomes large, concave and remarkably smooth in its middle part,with which blood-vessels are in close contact.
External end of the clavicle (acromial, distal)
Strongly flattened from top to bottom, the external end however includes only one rather smooth facet, less smooth than are in general the articular facets of the skeleton; this facet of elliptic form, with a large d antero posterior diameter, looks outwards, bellow and a little forward; it is cut in bevel at the expenses of the lower face of the bone and lies on a similar facet on the acromion.
Internal end of the clavicle (sternal, proximal)
Remarkable by its volume, this end is received in a sternochondral notch, dug on the side faces of the sternal manubrium and supplemented in a lower position by the higher face of the first costal cartilage by its contour, very projecting and irregularly triangular, it overflows the sternal notch frontward, backward and especially upward ; its posterior angle is inserted deeply in the thoracic cavity. The internal end of the clavicle is only articular in the part which answers the notch sternal, i.e. in the part former and lower in all the remainder of its extent it has depressions and roughnesses for the insertion of the ligaments and the articular meniscus. The cartilaginous facet, which is prolonged on the lower face of the bone, is convex transversely and very slightly concave from frontward to backward.
The sternal ends of two clavicles with epiphyses.
A, right clavicle form below and behind. B, left clavicle from below and behind. (From Royal College of Surgeoons Museum.)
Ossification of the clavicle
It is the clavicle which opens the ossification period of the skeleton oστεoν πρ oτoγευε, as the ancient anatomists would say It develops by two ossification centers: a primitive and a secondary or complementary. The primitive center appears between the thirtieth and the thirty-fifth day of the fetal life, a few days before those of the humerus and the femur: it develops with such a speed that the bone is to some extent invaded from the start, on all its extent, by limestones salts: the clavicle quickly acquires a length of 5 millimeters. In the second month of the fetal life, the clavicle is already 7 millimeters in length; it is then longer than the humerus and the femur; it is only about the middle of the third month that these bones will present an equal length to that of the clavicle. At birth, it reaches 4 centimeters (Rambaud and Renault): This primitive center forms, while extending, all the body and the external end of the bone; it is the diaphysis center.
The secondary or complementary ossification center appears between twenty and twenty-two years it is the last of the complementary centers to the members it is also that which is welded the last: this welding is carried out between twenty-two and twenty-five years old. It appears in the middle of the articular facet of the sternal end and forms only the thin osseous plate which models this end.
The mode of development of the clavicle differs from that of the other bones it is not preceded by a cartilaginous outline (Gegenbaur) the cartilage is formed only after the appearance of the first ossification center. This mode of development is in connection with the origin at the same time of the dermic and mesodermic of the bone on the man; in fish, it is a bone exclusively dermic or cutaneous.
Structure of the clavicle
The body of the clavicle is formed of a cylinder remarkably thick of compact tissue, containing a spongy tissue of broad areolas: the compact layer is thinned gradually towards the ends, primarily made up by spongy fabric covered with a thin compact layer. Towards one the average third of the bone, the spongy fabric rarefies, its areolas become larger are limited by thicker plates or trabecules, directed according to the length of the bone when this rarefaction is very accentuated, the clavicle appears dug by a medullary canal which occupies its average third and forever more than 3 to 5 centimeters length. On, body the compact layer is a little thicker along the concave edge than on the convex edge.
The fractures of the clavicle usually relate to the body, and generally with the junction of internal two thirds with the external third in this point the compact layer is still very thick: in fact thus characteristics of structure determine the ordinary place of these fractures either only the direction of the feature of fracture which always runs from top to bottom and of outside in inside I do not find that two exceptions has this rule on 30 fractured clavicles of my collection.
Connections of the clavicle
The clavicle is articulated inward with the sternum and the first costal cartilage, outwards with the scapula (acromion and coracoid).
Location of the muscular insertions on the clavicle
Upper surface: Sternocleidomastoid; deltoid; trapezoid.
Anterior surface: Subclavian.
Anterior border: Large pectoral deltoid.
Posterior border: Trapezoid; Sternocleidohyoidien.
Variations of the clavicle
The shape and dimensions of the clavicle vary according to the sexes, the individuals and the professions. The clavicle of the woman is generally spindlier than that of the man: its curves are accentuated; its absolute length is less. The profession has as much influence as the sex on the form and the force of the clavicle the exercise develops the bone, the rest the atrophy after the disarticulation of the upper limb, the clavicle decreases in all its dimensions. The atrophy or the absence, congenital, seldom observed, usually accompanies the stops by development of the upper limb.
- The extent of these surfaces or prints of insertion varies with the development of the muscles sometimes they are very isolated, sometimes they are contiguous in this last case 'E third external of the clavicle disappears under the trapezoid and the deltoid which are continued without apparent interruption.
- Abnormally the lower face can still present two facets resulting from the contact of the clavicle with the first rib and the coracoid process the costal facet, little marked, meets then beside the costoclavicular print; the coracoids facet is in front of the tuber of the conoid ligament, it can be very prominent and take the shape of a round eminence with oval outline. These anomalies, well studied by Gruber and Luschka, are far from being rare I have met many examples of it.
- It is difficult and sometimes impossible to see these details on a great number of clavicles, from which the epiphysis was detached during the preparation on these bones, the internal end shows its spongy substance at the bottom of a fossa limited by a very prominent triangular outline.