THE THIGH, FEMUR, AND HIP-JOINT.
The femur: its superior extremity: _neck_, _head_, and
_trochanters_.--Hip-joint, or _coxo-femoral articulation_;
movements of the joint; limits of these movements; limits
of extension (ilio-femoral ligament); adduction (ligamentum
teres); the influence of atmospheric pressure (experiments of
the brothers Weber).--The transverse dimensions of the hips and
shoulder in the male and female; the various formulæ (ovoid of
the ancients, ovoid and elliptical of Salvage); the correct
formula; the inter-humeral and inter-trochanteric diameters; the
inter-acromial and inter-iliac diameters.--The external form of
the region of the hips and great trochanter in particular; the
osseous prominences brought into relief on the surface as flat
and depressed surfaces.
The femur (Figs. 39 and 43), or bone of the thigh, is one of the long
bones. It is the largest bone in the skeleton, and consists, like all
the long bones, of a shaft and two extremities (Fig. 39). In this
chapter we have to consider its upper end, and its articulation with
the hip-bone.
[Illustration: FIG. 39.
VERTICAL SECTION OF FEMUR.--1, 1, 2, 2, the body of the bone
with the medullary canal hollowed out;--3, the great trochanter,
whence the neck is given off, terminating in the head;--4,
inferior extremity of the bone.]
The upper extremity of the femur is composed of a _head_, a _neck_,
and of two tuberosities (the _great_ and _small trochanters_) placed
at the junction of the neck with the body of the bone. The head of the
femur (5, Fig. 43) is regularly rounded, and forms three-fourths of a
sphere. Its spherical surface, turned inwards, upwards, and forwards,
is smooth and covered with cartilage, except at a pit (6, Fig. 43) seen
a little below and behind its centre, which gives attachment to the
_ligamentum teres_--a strong fibrous band which connects the femur to
the acetabulum.
The neck of the femur (7, Fig. 43), connecting the head with the
shaft, is directed downwards and outwards in the form of a cylinder,
flattened a little from front to back, to become attached to the
upper extremity of the shaft of the femur at an obtuse angle, looking
downwards and inwards (Fig. 39). This angle which the axis of the neck
makes with that of the body varies in different individuals. In the
adult male it is about 135 degrees; in the female it is less open--that
is, it approaches nearer to a right angle. This helps to increase the
transverse diameter of the hips in the female. Again, in both sexes
this angle approaches gradually to a right angle with the advance of
age--a change that assists in shortening the total height in the aged.
At the junction of the neck of the femur with the body of the bone are
the two tuberosities, or trochanters--one situated above and to the
outer side, called the _great trochanter_ (3, Fig. 39; and 8, Fig.
43); the other situated below and to the inner side, at the junction
of the neck and the shaft, called the _lesser trochanter_ (10, Fig.
43). The great trochanter is of large size, is quadrilateral in shape,
and projects beyond the upper border of the neck. It presents on its
surfaces and borders numerous impressions, for the insertion of the
muscles of the buttock. The lesser trochanter, on the contrary, is
smaller in size, mammillated or conical in shape, and gives attachment
to the psoas and iliacus muscles only.
_The Hip-joint._--The _ilio-femoral_ or _coxo-femoral_ articulation is
formed by the reception of the head of the femur into the cavity of
the acetabulum, in which it exactly fits. The edge of the cavity is
surrounded by the _cotyloid_ and _transverse ligaments_, which clasp
the head of the femur and serve to deepen the cavity and narrow its
orifice. The articulation is a ball and socket joint (enarthrosis).
As we should expect from the form of the articular surfaces, every
possible description of movement can take place: the head of the femur
can glide in all directions in the cavity in which it is received,
producing the movement of _abduction_ (the inferior limb being carried
outwards, away from the middle line), _adduction_ (towards the middle
line), _flexion_ (forwards, the anterior surface of the thigh being
brought towards that of the abdomen), _extension_ (backwards), and
rotation, of the femur, outwards and inwards. But these movements are
variously influenced by the disposition of the ligaments of the joint.
Some are limited, others are very extensive.
The ligamentous apparatus of the hip-joint consists of a thick capsule
of fibrous tissue, which arises from the margin of the cotyloid cavity
and encloses the head and neck of the femur. The disposition of this
capsule is very different in front and behind.
The capsule is composed of superficial longitudinal fibres stretching
from acetabulum to femur, and thickened, except posteriorly, to
form strong ligaments; and deeper, circular fibres, which _alone_
constitute the back part of the capsule--consequently the capsule
is thinner and weaker at the back, where the circular fibres appear
superficially--constituting the _zona circularis_, or _ligament of
Bertini_. The posterior portion of the capsule consequently cannot
at any time become tense. The movement of flexion, indeed, may be
continued as far as possible without causing tension of the back of
the capsule of the joint. It is for this reason we speak of flexion of
the thigh as unlimited, and, in fact, it may be continued until the
anterior surface of the thigh comes in contact with the abdomen.
The other movements of the thigh at the hip-joint are limited by the
several longitudinal ligamentous bands of the capsule. In front, the
capsule of the joint is put on the stretch when the thigh is carried
backwards during extension, and the movement is checked when it arrives
at a certain point. This is due to the _ilio-femoral_, or _Y-shaped
ligament of Bigelow_, which extends from the acetabular margin to
the front of the neck of the femur, dividing as it descends into two
bands. It is the most important ligament of the hip-joint. Owing to the
strength of this ligament, the movement of extension can be limited and
checked at any given moment. Now if we try the experiment on ourselves,
having flexed the thigh on the abdomen and then gradually extend it,
we shall perceive that the movement is arrested at the moment when the
axis of the thigh is in a continuous line with that of the body (or if
the subject is upright, when the thigh is vertical). If we repeat this
experiment on the dissected subject, with the joint prepared, we see
that the ilio-femoral ligament is relaxed when the thigh is flexed on
the pelvis, and becomes tense in proportion as the bone is extended,
and that this tension arrives at its maximum when the femur is found
in a line with the trunk, and the ilio-femoral ligament presents an
insurmountable obstacle to any further extension.
It is true that a man in the upright position can move his thigh
backward; but it is necessary to observe, if, for example, it is the
right thigh which is carried backward, it is not in the right hip-joint
that the movement takes place, but in the left; in other words, the
trunk is flexed upon the left femur. We may therefore state that when
the thigh is so extended as to be in the same continuous plane with the
trunk, the thigh and trunk form one and the same piece, and the two
parts are incapable of further extension; and, consequently, when one
thigh is carried behind the vertical line, the trunk must be rotated to
an equal extent on the opposite side.
The ilio-femoral band plays also an important part in the maintenance
of the erect attitude. Being stretched in extension of the thigh, the
head and neck of the femur rest against it, and so the erect position
can be maintained without excessive muscular exertion. The ilio-femoral
ligament also, aided by the _pubo-femoral_ band of the capsule,
presents an obstacle to _abduction_, or the movement of the thigh
outwards, in the upright position, when the ligament is tense. When the
thigh is slightly flexed on the pelvis, and the ligament is relaxed
abduction of the thigh becomes comparatively easy (Fig. 40).
[Illustration: FIG. 40.
OUTLINE OF BUTTOCK AND THIGH.]
The movement of _adduction_, or bringing of the thighs together, is
limited by the _ilio-trochanteric_ band of the capsule, and by the
_ligamentum teres_--a special ligament, not part of the capsule,
contained within the joint. This movement becomes very easy if the
joint is slightly bent. If we try the experiment on an articulation
in which the ilio-femoral ligament is cut, we perceive that in the
position of extension the movement of adduction is just as difficult
as if the ligament were intact. This is due to the presence of the
_ligamentum teres_. This ligament is attached by one extremity to
the rough depression below and behind the head of the femur, and
by the other extremity, which is bifurcated, to the margins of the
acetabular notch. We have already seen that in the pelvis of a man in
the upright position this notch looks directly downwards (page 106);
the ligament in this position is also vertical, and is put on the
stretch, as the two ligaments, so to speak, help to suspend the pelvis
on the heads of the femora. Now, in the upright position, the femur
being vertical, the movement of adduction could be produced only by a
gliding movement of the head of the femur in the acetabular cavity;
but this gliding movement cannot take place, as the head of the femur
is kept in position by the tense, round, or suspensory ligament. If,
on the contrary, the femur is slightly flexed, the round ligament will
be found relaxed; this permits the gliding of the head in the cavity,
and at the same time permits of adduction, a movement which may now
be accomplished with ease. An experiment which proves these facts
without giving an anatomical demonstration of them (obtainable only
from a prepared subject) is very easy to accomplish upon oneself. If
one stands perfectly upright, rigid, with the body thrown backwards as
far as possible, it will be seen that it is almost impossible to bring
the two thighs and knees close together. Adduction is almost entirely
lost in this position, so that we should be unable to bring the knees
together and crush a fragile body, such as an egg, placed between them.
But if, on the other hand, we flex the thighs a little, or the trunk is
bent on the thighs, adduction becomes extremely easy, and now we can
knock the knees together without any difficulty.
The hip-joint is remarkable for the fact that upon it we can most
conveniently demonstrate a law which applies also to all the other
articulations, but of which we have reserved the explanation until
now--namely, the law relative to _the influence of atmospheric pressure
in maintaining articular surfaces in contact_. Up to the present, in
studying the articulations, we have spoken of the form of the articular
surfaces, and from their outline we have been able to deduce the
nature of the movements permitted in the joint; we have spoken of the
ligaments which surround the joint, and from their arrangement we have
been able to infer the limits imposed upon these movements. But we have
not spoken of the conditions which enable one articular surface to
glide upon another without separating, and which maintain the surfaces
in intimate and permanent apposition. It might be thought that this
function devolves on the ligaments, but this would be an error; it is
_atmospheric pressure_ which keeps up this contact.
The head of the femur is fitted very exactly into the hollow of the
acetabulum. In the first place, the head of the femur is in close
contact with the cavity, the non-articular portion of which is filled
up by adipose tissue. In the second place, the cotyloid ligament
closely encircles the base of the head of the femur, and may be
compared to the edges of a cupping-glass. Now, as a vacuum exists
between the two articular surfaces, and the air cannot penetrate
between them, they adhere very closely to each other, merely allowing
one to glide on the other; but if by any means air is allowed to obtain
access to the interior of the joint the bones naturally fall apart. The
experiments which explain those facts were first demonstrated by the
brothers Weber.
We have felt it important to dwell here, once for all, on the important
part which atmospheric pressure plays in the mechanism of joints.
Analogous experiments show that this pressure plays comparatively
the same part in other articulations in maintaining their articular
surfaces in contact.
MEASUREMENTS AND PROPORTIONS OF THE HIPS.--To return to the study of
the region of the hips, we must now examine the _transverse dimensions_
of this region, and the _external forms_ which result from the presence
of bony prominences, especially the great trochanter of the femur.
The _transverse distance_ which separates the one great trochanter of
the femur from the other should be compared with the distance between
the heads of the humeri; in other words, we must compare the _diameter
of the hips_ with that of the _shoulders_.
What strikes us most in this comparison, at the first glance at a
series of skeletons, is the great projection which the hips form in
the female. In order to express this difference, various formulæ have
been proposed. In one such formula the trunk is regarded as a figure
more or less regularly oval, of which one extremity corresponds to the
shoulders, the other to the hips, and in the two sexes the diameter
is greater at one end than at the other. The ancients expressed the
formula in the following manner:--In the male and in the female the
trunk represents an ovoid--that is to say, an oval similar to that of a
figure of an egg having a greater and a smaller extremity. In the male
this figure has its greater end above, while in the female the lower is
the larger end. According to this formula, in the female the diameter
of the hips exceeds that of the shoulders, while in the male it is the
diameter of the shoulders which exceeds that of the hips. The formula,
as regards the female at any rate, is evidently exaggerated. In fact,
Salvage and Malgaigne proposed the following formula:--Allowing that
the trunk of the male is an ovoid, with the greater extremity superior,
the trunk of the female forms an ellipse--that is to say, a figure in
which both extremities are of the same dimensions; so that while in the
male the diameter of the shoulders exceeds that of the hips, in the
female the diameter of the hips is just equal to it.
Now this last formula also exaggerates the real proportions of the
hips in the female. The correct formula is as follows:--In the
male, as well as in the female, the trunk represents an ovoid with
the greater diameter above; but while in the male the difference
between the greater extremity and the smaller is very considerable,
in the female this difference is very slight. We can see by actual
measurements that in the female the diameter of the hips, though always
less, differs very little from that of the shoulders. In the male,
the distance from the head of one humerus to the corresponding part
on the opposite side (_inter-humeral diameter_) is on the average 15¼
inches, and the measure taken from one great trochanter to the other
(_inter-trochanteric diameter_) is 12¼ inches; a difference between
the two diameters of about one-fifth. In the female, the inter-humeral
diameter is on the average 13¾ inches; the inter-trochanteric
diameter is 12½ inches; therefore there is between the two diameters
a difference of about one-twelfth. These figures also serve to
demonstrate that the diameter of the shoulders is greater in the male
than in the female (15 to 14), and that inversely the diameter of the
hips is greater in the female than in the male (12½ to 12¼); so that,
accordingly, if a man and a woman of average stature are supposed to
throw their shadow on the same portion of a screen, the shadow of the
shoulders of the male would cover a much larger surface than the shadow
of the shoulders of the female; and, on the contrary, the shadow of the
hips of the woman would exceed the shadow of the hips of the man, but
only to a very small extent.
In the foregoing paragraphs we have dealt with the transverse
hip-measurements as inter-trochanteric. There is, however, another
method of measurement, which justifies to a certain extent the formulæ
adopted by the authors previously mentioned; it consists in comparing
on the skeleton in both sexes the diameter of the pelvis without the
femora with the diameter of the shoulders without the humeri. In this
instance the shoulders are represented by the _inter-acromial_, and
the hips by the _inter-iliac diameter_ (from one iliac crest to the
other). Under these circumstances the exact measurements show that in
the male the inter-acromial diameter is 12¾ inches, and the inter-iliac
11 inches; therefore, as in the other formula, the trunk, deprived of
its members, still represents an ovoid, with its greater extremity
superior. On the other hand, in the female, the inter-acromial diameter
is 11½ inches, and the inter-iliac measurement is 12 inches; so that
here the trunk, deprived of its members, represents an ellipse or an
ovoid, with its greater extremity below, although the upper extremity
differs very little in size from the lower. The fault of this method of
measurement is that it does not explain things as they are. The artist
does not contemplate the torso as otherwise than complete--that is to
say, provided with the upper and lower limbs--and it is absolutely
necessary to take into account the part which the head of the humerus
and the great trochanter of the femur take in the formation of the
contours of the shoulder and hips. We have thought it desirable,
however, to demonstrate this mode of measurement, because of the clear
illustration which it gives of the greater diameter of the female
pelvis as compared with that of the male.
If we arrange in a table the figures given above for the inter-humeral,
inter-trochanteric, inter-acromial, and inter-iliac diameters in the
male and in the female, or if, better still, we represent those figures
by lines intended to express, on the profile of a man and that of a
woman, the proportionate value of the diameters of the region of the
shoulders compared with the diameters of the pelvis and the hips, we
obtain two figures which express in a striking manner all that has been
pointed out (Figs. 41 and 42).
[Illustration: FIG. 41.
Diagram comparing the diameters of the hips with the diameters
of the shoulders in the male.]
[Illustration: FIG. 42.
Diagram comparing the diameters of the hips with the diameters
of the shoulders in the female.]
We see, in fact, that in the male subject (Fig. 41) the vertical
lines (_y_ and _y_) passing through the extremities of the
inter-trochanteric (_d d_) and the inter-iliac (_c c_) diameters,
both fall within the extremity of the inter-humeral (_b b_), and also
the inter-acromial diameter (_a a_); on the contrary, in the female
(Fig. 42) we find that these same vertical lines both fall within the
extremities of the inter-humeral (_b b_), but on the outer side of the
inter-acromial (_a a_) diameter.
_The Great Trochanter._--A word is necessary concerning the influence
of the great trochanter of the femur on the external form of the hip.
Looking at the skeleton the great trochanter is seen to stand out so
clearly and forms a projection so considerable that we should expect
to see on the model a prominence corresponding to its shape. This,
however, is not so. The gluteal muscles which proceed from the pelvis
to be attached to the great trochanter are numerous and thick, and
the fleshy bellies of the more superficial form a projection which is
raised above the trochanter; while over the process they are replaced
by tendons, more or less flattened, so that the trochanter is marked on
the surface by a depression bounded by the muscles--the tensor vaginæ
femoris in front, the glutei muscles above and behind. Below, the
concave space corresponding to the great trochanter is continuous with
the broad, flat surface which occupies the outer aspect of the thigh.
There are many analogous cases where osseous projections are frequently
marked on the external figure by a depression, and the reason is
always the same as that just explained, that these osseous projections
give insertion to muscles, the fleshy bellies of which give place to
tendinous expansions at a little distance from them, and form by their
thickness a raised surface round the prominence; in a general way,
then, we may say that, with a few exceptions (such as the malleoli of
the ankle-joints), wherever an osseous surface is covered over only
by the skin, the muscles which surround this surface arise above its
level, and in consequence the bone is marked by a depression, more or
less pronounced as the subject is more or less muscular. Similarly, the
middle portion of the sternum is marked superficially by a depression
limited on each side by the swelling of the great pectoral muscles, and
the internal surface of the tibia forms a long and broad groove when
the anterior and posterior muscles of the leg are well developed.