THE THIGH AND KNEE.
The bony structure of the thigh and knee.--Shaft of femur:
its curvature; oblique direction; linea aspera.--Lower
extremity of femur: condyles; inter-condyloid notch; patellar
surface.--_Patella_: ligament of the patella.--Upper parts of
the bones of the leg.--_Head of the Tibia_: tuberosities and
tubercle.--Head of _fibula_.--Articulation of the knee; relation
of the bones in flexion and extension.--Ligamentous apparatus;
capsule; its laxity and extent in front, whence the facility
and extent of movement in flexion; its strength and shortness
behind, whence the limit of movement in extension.--Lateral
ligaments of the knee: their special mechanism.--Lateral
movements of the knee: crucial ligaments.--Form of the region
of the knee: surface below the patella; projection of patella;
ligament of patella.--Osseous projections on the external
surface and the insertion of tendons.--Simplicity of the form of
inner surface of the knee.
Having studied the upper extremity of the femur with regard to the
articulation, proportions, and contour of the region of the hips,
we shall continue the study of this bone by examining its _shaft_
and _inferior extremity_, and this latter part brings us to the
_articulation of the knee_.
The shaft of the femur is not straight, but is distinctly curved, with
its convexity forward and outwards. On the living model this convexity
may be recognised in the form of the anterior surface of the thigh,
which is distinctly convex in front and on the outer side, the muscles
which cover the femur in front being disposed in such a manner as to
increase this appearance still more, as their fleshy masses are grouped
together in the middle line of the anterior region of the thigh.
The outward projection is most marked in cases of excessive muscular
development, and is consequently more obvious in the male than in the
female, and is best shown in the limbs of athletes. Again, the femur,
in the model when standing upright, is not directed vertically, but
rather obliquely from above downwards and inwards (Fig. 43), so that
the superior extremities of the femur are placed at some distance,
comparatively speaking, from each other, while the lower extremities
come very near each other at the level of the knees. In the female
this obliquity is more clearly marked than in the male, for the upper
extremities of the two bones are in the former placed more widely
apart, as we have already seen when demonstrating the relative diameter
of the hips (inter-trochanteric diameter) in the female.
[Illustration: FIG. 43.
LEFT FEMUR (posterior view).--1, 1, linea aspera;--2, 2, its
external superior bifurcation;--3, its internal superior
bifurcation;--4, 4, its inferior bifurcations;--5, head of
femur;--6, depression in the head giving insertion to ligamentum
teres;--7, neck of femur;--8, great trochanter;--9, internal
surface of great trochanter;--10, small trochanter;--11,
external condyle;--12, internal condyle;--13, inter-condyloid
notch;--14, 15, tuberosities surmounting each of these condyles.]
The shaft of the femur presents three surfaces--one anterior, one
postero-external, and one postero-internal; and three borders, two
lateral and one posterior. The two lateral borders are very rounded,
not sharp; the posterior border, on the contrary, is very prominent,
and forms a rough line, called the _linea aspera_ (1, Fig. 43), which
gives insertion to a number of muscles. This linea aspera divides above
into two _bifurcations_ slightly diverging, of which the outer one (2,
2, Fig. 43) proceeds towards the great trochanter (_gluteal ridge_),
and the inner one passes towards the lesser trochanter. Below, the
linea aspera bifurcates in the same manner, one of its branches going
to the inner, the other to the outer condyle of the femur (4, 4, Fig.
43).
The _inferior extremity_ of the femur is widely expanded, both in
the transverse and in the antero-posterior diameter. When we examine
the posterior aspect of this extremity (Fig. 43) we see that it is
formed by two large prominences directed backwards, which are termed
the _external and internal condyles_. These project laterally, and
the inner condyle is much more prominent than the outer. The inferior
and posterior surfaces of these condyles are smooth and covered with
articular cartilage; between them is a deep hollow behind called the
_inter-condyloid notch_ (13, Fig. 43). When we examine the anterior
surface of the lower end of the femur we see that the condyles are
united, and their smooth and continuous articular surface, covered
with cartilage, serves to articulate with the knee-cap. This is the
_patellar_ surface. This surface presents a depression in the middle
line and two lateral lips, of which the external, continuous with the
external condyle, is more prominent and rises higher than the internal,
which is continuous with the internal condyle. These details are very
important, for, as we shall see, the lips of the patellar surface show
prominently beneath the skin when the knee is strongly flexed, and we
can notice their differences in prominence and height.
In forming the articulation of the knee, the lower end of the femur is
in direct contact with the patella and the upper end of the tibia, and
is connected (by ligaments) with the upper end of the fibula. We will
now consider the patella and the upper extremities of the two bones of
the leg.
The _patella_, which has been compared to a disc (whence its name),
is more nearly triangular in shape, presenting an anterior surface
longitudinally striated and slightly convex, and a posterior surface
moulded on the patellar surface of the femur, and forming an oval
articular surface with a median ridge and two lateral hollows. The
borders of the patella are three: two lateral oblique borders for the
attachment of muscles and ligaments; and a base directed upwards,
into which the tendon of the quadriceps extensor (and particularly
the rectus femoris) is inserted. The apex of the bone is directed
downwards, and attaches a strong ligament which is inserted into the
tubercle of the tibia, and is termed the _ligament of the patella_.
Properly speaking, this ligament is a continuation of the tendon of the
rectus femoris muscle. The patella should be considered as a _sesamoid_
bone, an osseous nodule developed in the substance of this tendon.
[Illustration: FIG. 44.
THE TWO BONES OF LEFT LEG (anterior view).--1, shaft of
tibia;--2, 3, its internal and external tuberosities;--4, spine
of tibia;--5, tubercle of tibia;--6, shin;--7, lower end of
tibia, with internal malleolus (8);--9, shaft of fibula;--10,
its upper end;--11, its lower end or external malleolus.]
The leg, like the forearm, is composed of two bones. One, the larger
of the two, is placed on the inner side (1, Fig. 44)--the _tibia_, or
_shin-bone_; the other, much shorter, is situated on the outer side,
and a little behind--the _fibula_ (9, Fig. 44). As in the case of the
two bones of the forearm, the bones of the leg end at different levels
above and below. Above, the tibia rises higher than the fibula, and
alone takes a direct part in the articulation of the knee; below, the
fibula extends lower than the tibia--so that the outer ankle (_external
malleolus_) descends lower than the inner one. We will now for a moment
examine the upper extremities of the two bones.
The upper extremity of the tibia is expanded from side to side, to
form the _tuberosities_ (internal and external), surmounted by two
_articular surfaces_, external and internal (2, 3, Fig. 44), for
articulation with the corresponding femoral condyles. The non-articular
interval between these two surfaces presents in its centre a projection
like a bifurcated cone which is known as the _spine_ of the tibia. In
front of the spine and behind it are rough triangular surfaces for the
attachment of the _crucial ligaments_.
The circumference of the upper end of the tibia forms a broad rough
margin for attachment of the capsule of the knee-joint. In front, it
is prolonged downwards into a large triangular surface which ends in
a rounded eminence, called the _tubercle_ of the tibia, which gives
insertion to the ligament of the patella previously mentioned. On the
outer side and back of the external tuberosity is a rounded facet,
smooth and covered with cartilage, and directed mainly downwards for
articulation with the head of the fibula (10, Fig. 44). Lastly, on
the back of the bone is the _notch_ of the tibia, separating the two
tuberosities from one another.
The upper end of the fibula forms (10, Fig. 44) an irregular rounded
knob. It is situated external to and rather behind the upper end of
the tibia, and articulates, as already seen, by its upper surface with
the outer tuberosity of the tibia. External to the articular surface
is a smooth area for the attachment of the biceps tendon, and the
long external lateral ligament of the knee. Behind this area is the
_styloid process_, which gives attachment to the short external
lateral ligament of the knee. The head of the fibula can be plainly
felt through the skin, below and behind the head of the tibia.
Such are the bony structures which take a direct (femur, tibia,
patella) and indirect part (fibula) in the conformation of the
knee-joint. In the living model, in the erect posture, the condyles of
the femur rest by their inferior surfaces on the upper surface of the
tibia, and the apposition of the articular surfaces is rendered more
exact by the presence between the articular surfaces of the femur and
tibia of two _semi-lunar fibro-cartilages_, which increase the depth
of the tibial surfaces (5, 5, Fig. 46), so that the corresponding
condyle of the femur is received into a true articular cavity. At the
same time, the patella is closely applied to the confluent anterior
surface of the lower end of the femur. When, on the other hand, the
model is kneeling, or, more generally, when the leg is flexed (carried
backwards), the patella, which is firmly fixed to the tibia by its
ligament, glides downwards on the femur, and comes in contact with the
lower part of its anterior surface at the same time that the posterior
parts of the condyles in turn roll over the upper surfaces of the tibia.
[Illustration: FIG. 45.
THE ARTICULAR PARTS OF THE KNEE (antero-posterior section).--1,
femur;--2, tibia;--3, fibula;--4, patella;--5, rectus
tendon;--6, ligament of patella;--7, one of the crucial
inter-articular ligaments;--8, 8, one of the muscles of the
calf;--_a_, _a_, anterior part, and _b_, posterior part of the
articular capsule;--_C_, adipose mass beneath patella.]
After this rapid sketch of the bones which enter into the formation
of the knee-joint, we have now to study in detail its ligamentous
apparatus. The ligamentous apparatus of the knee is essentially
composed of a fibrous _capsule_, attached to the borders of the
articular surfaces of the femur, patella, and tibia. It is strengthened
on all sides by the tendons of muscles attached to these bones in the
neighbourhood of the knee. Without entering into unnecessary detail, we
must consider the arrangement of this capsule, and its disposition on
its anterior, posterior, and lateral aspects, and then consider how it
affects the movements of the knee-joint, rendering some movements easy
and extensive, while it limits others or makes them almost impossible.
In front (_a a_, Fig. 45) the capsule is loose and expanded and is
mainly formed by the insertion of the quadriceps extensor muscle into
the patella, with its continuation to the tubercle of the tibia as the
ligament of the patella. This arrangement accounts for the ease and
extent of the movement of flexion. In this movement, the tibia being
carried backwards, and drawing with it the patella in the relaxed
condition of the quadriceps extensor muscle, the capsule of the joint
is put on the stretch. It would curtail the movement of flexion if it
were short and compact; but the capsule at this point is so expanded
and loose that no increase of movement on the part of the leg can cause
any tension. Thus flexion of the knee may be prolonged until the calf
of the leg comes in contact with the posterior surface of the thigh.
Behind, the capsule of the joint is short and thick, and consists of a
strong _posterior_ ligament. When the leg is flexed on the thigh, this
ligament is relaxed; but as the leg passes from flexion to extension
it becomes tense, and when extension has arrived at that point which
brings the leg in direct continuation with the thigh, no further
movement is possible in a forward direction, and the limb is therefore
fixed in this position.
There are, moreover, other important ligaments which act, and still
more forcibly, in the same manner; namely, the internal and external
lateral ligaments of the joint, which must now be considered.
[Illustration: FIG. 46.
THE KNEE state of the lateral ligaments (_a_, _b_) during
flexion.--1, femur;--2, condyle of femur;--3, tibia;--4,
fibula;--5, 5, section of semi-lunar fibro-cartilage.]
[Illustration: FIG. 47.
THE KNEE: lateral ligaments tense during extension of the leg
on the thigh (the distance, _a b_, is greater here than in
preceding figure); for the lettering, see preceding figure.]
The _internal lateral ligament_ is a broad band of fibres, which passes
from the inner tuberosity of the femur over the inner tuberosity of the
tibia to be attached to the upper part of the _shaft_ of the tibia on
the inner side. It helps to form the contour of the inner side of the
knee.
The _long external lateral ligament_ is a rounded cord, very strong and
quite distinct from the capsule. Its inferior extremity is not inserted
into the tibia, but into the head of the fibula between the insertions
of the biceps muscle (Figs. 46, 47, _a_, _b_). The most remarkable
characteristic of these ligaments is that their upper ends, attached to
the lateral surfaces of the condyles of the femur, are not inserted at
the centre of the curve of the condyles, but at a point situated more
posteriorly (_a_, _b_, Figs. 46 and 47). During flexion these ligaments
are therefore relaxed, but as extension is produced, as the tibia is
carried forward on the curved surface of the condyles of the femur,
these ligaments gradually become tense, their points of insertion
becoming further and further apart, owing to the eccentric insertion
of their superior extremities. When the leg reaches that position of
extension in which it is in line with the femur, the tension of the
lateral ligaments is such as to arrest its movement and completely fix
the leg in relation to the thigh. This may be seen by comparing Figs.
46 and 47. We see, then, that owing to the position of the anterior,
posterior, and lateral ligaments of the knee-joint, the movement of
flexion in this joint is very extensive, while that of extension is
limited, as it cannot be prolonged further than the position which
brings the leg into direct continuity with the thigh.
These ligaments are also responsible for the amount of _lateral
movement_ and _rotation_ possible in the knee-joint. This articulation
being formed by two condyles, it is very evident that lateral flexion
cannot be produced, for then it would be necessary for one of the
condyles to become detached from the corresponding articular surface of
the tibia. Lateral movement is thus impossible, but a slight gliding
movement under certain conditions takes place between the condyle of
the femur and the tibia, a movement produced by a _rotatory_ movement,
of which the other condyle forms the centre. These slight movements
of rotation, which contribute to the motion by which we direct the
point of the foot outwards or inwards, are impossible during complete
extension, when the tibia is fixed on the femur by the tension of
the lateral ligaments and the posterior part of the capsule, and all
the parts have already arrived at their maximum of tension. But when
flexion occurs, and especially when the leg is at a right angle to the
thigh, as in the seated subject, slight movements of rotation of the
leg become possible; they are of small extent, it is true, especially
inwards; since it is easier for the knee to take part in the movement
which turns the foot outwards, than that which turns it inwards. This
difference between rotation inwards and outwards is due to the presence
within the joint of two ligaments called the _crucial ligaments_, of
which we will only mention that they arise from the upper end of the
tibia, between the two articular surfaces (page 136), and, crossing
one another, are attached above to the sides of the inter-condyloid
notch of the femur on the corresponding surface of each condyle. This
crossing of the two ligaments is increased by the rotation of the tibia
inwards, as this movement tends to twist them one on the other, and fix
the tibia, so as to prevent rotation of the leg inwards. On the other
hand, rotation outwards unwinds these ligaments and renders them more
relaxed; so that this movement could be very extensive if the lateral
ligaments did not prevent too great displacement between the condyle of
the femur and the corresponding surface of the tibia.
There are still in relation to the knee-joint several anatomical
particulars which must now be examined in relation to _the external
form_ of the living model.
The posterior surface of the knee is covered by numerous muscles and
tendons which form the boundaries of the ham or _popliteal space_;
the study of this region will therefore be undertaken along with the
description of the muscles of the leg and thigh. On the outer and inner
surfaces, and on the front of the knee-joint, however, many details of
outward form are caused solely by the osseous and ligamentous parts, to
which we must now draw particular attention.
[Illustration: FIG. 48.
OUTLINES OF THE LOWER LIMB.--A, From behind; B, from the front;
C, from the outer side.]
The anterior surface of the knee alters in shape in the two positions
of extension or slight flexion, and in forcible flexion. In forcible
flexion we notice particularly the form of the articular lower end of
the femur (see page 134). In extension we find on the anterior surface
of the knee, in succession from above downwards, a _flat triangular
space above the patella_, corresponding to the tendon of the rectus
femoris muscle; next, the _prominence of the patella_, showing clearly
beneath the skin its triangular shape, with the base above and apex
below; the two superior angles of the patella are frequently very
distinct in the form of two small rounded projections. Below, _the
ligament of the patella_ forms a longitudinal eminence in the middle
line, reaching to the tubercle of the tibia, which is seen (in
semi-flexion) as a large projection. But, again, we frequently perceive
on each side of the ligament of the patella a slight, soft eminence,
easily depressed, which corresponds to parts not yet mentioned. These
are the thin lateral portions of the capsule (_lateral ligaments of
the patella_), which extend from the sides of the patella and patellar
ligament to the tibial tuberosities. These portions of the capsule
(_c_, Fig. 45) are thin, and cover a _large mass of adipose tissue_,
which is prolonged into the interior of the joint (as the _alar
ligaments_), and which forms packing for the articulation on either
side of the ligament of the patella (6, Fig. 45). When the quadriceps
extensor muscle draws forcibly on the patella and its ligament, these
compress this adipose mass to a much greater degree, so as to form a
bulging on each side, and then the bilateral prominence in question is
much more clearly marked.
On the external lateral surface of the knee we note the osseous
prominences of the _tubercle of the tibia_ (seen here in profile)
and its _external tuberosity_; behind and below, _the head of the
fibula_; and above, the _external condyle of the femur_. To certain
of these prominences are attached the tendons coming from the thigh,
marked on the external surface of the knee by three strong vertical
bands; viz.:--in front, the tendon of the patella (seen here in
profile); behind, the tendon of the biceps femoris, proceeding to be
inserted into the head of the fibula; and between them the part of the
aponeurosis of the deep fascia of the thigh, which becomes narrow and
thickened, and forms a true tendon--_the ilio-tibial band_--attached to
the outer tuberosity of the tibia.
The form of the internal aspect of the knee is simple. Here the
internal condyle of the femur and the corresponding tuberosity of
the tibia form together a large regular hemispherical surface. The
internal lateral ligament forms a broad band (page 139), which sweeps
over the inner tuberosity of the tibia, accompanied by the tendons
of the sartorius, gracilis, and semi-tendinosus muscles, to become
inserted into the upper portion of the shaft of the tibia. The ligament
and tendons soften the outlines of the bones, and give a rounded
contour to the inner side of the knee.