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the interior of the articular cavity and a bursa which lies under cover of the medial head of the gastrocnemius muscle.

The epiphyseal line of the distal end of the femur is partly intra-capsular and partly extra-capsular ; that of the proximal end of the tibia is extra-capsular.

Ligamentum Patellæ.—The ligamentum patellæ or anterior ligament (Fig. 318) is a powerful flattened band, attached proximally to the apex and adjoining margins of the patella, and distally to the rough anterior tuberosity at the proximal end of the shaft of the tibia. This ligament also serves as a tendon of insertion for the quadriceps extensor muscle, and a certain number of the fibres of the tendon may be observed to run distally as a thin fibrous covering for the anterior surface of the patella. The deep surface of the tendon is separated from the front of the head of the tibia by a synovial bursa, and proximal to this it rests upon the infra-patellar pad of fat, which is placed between the tendon and the synovial stratum of the joint.

The ligamentum posterius posterior (ligament) (Fig. 318) is a compound structure of unequal strength, and those portions by which it establishes continuity with the lateral parts of the articular capsule are remarkably thin. It is attached proximally to the popliteal surface of the femur, close to the intercondyloid notch, with lateral extensions to the non-articular areas immediately proximal to the posterior articular margins of the two condyles, where it is closely associated with the origins of the gastrocnemius muscle.

Distally it is attached to the rough non-articular posterior border of the head of the tibia, where, to its fibular side, it presents an opening of exit for the tendon of the popliteus muscle (Fig. 318).

The tendon of insertion of the semi- membranosus muscle contributes an important expansion which augments the posterior ligament on its superficial aspect. This expansion—lig. popliteum obliquum-passes obliquely proximally and laterally to lose itself in the general ligament, but it is most distinct in the region between the femoral condyles, where it may present proximal and distal arcuate borders (lig. popliteum arcuatum). A number of vessels and nerves perforate this ligament, and hence it presents a number of apertures.

Lig. Collaterale Tibiale.-The tibial collateral ligament (0.T. internal lateral) (Figs. 317 and 318) is a well-defined, strong, flat band which is applied to the medial side of the knee-joint, and is rather wider in the middle than at either end. It is frequently regarded as consisting of two portions—an anterior or long portion, and a posterior or short one. The two parts arise close together from the medial epicondyle, immediately distal to the adductor tubercle. The short or posterior portion passes distally and slightly backwards, to be attached to the postero-medial aspect of the medial part of the tibia proximal to the groove for the semimembranosus tendon. The long or anterior portion inclines somewhat forwards, and extending distally superficial to the tendon of the semi-membranosus, it is attached to the proximal part of the medial surface of the shaft of the tibia distal to the level of the tuberosity.

On its superficial aspect the tibial collateral ligament is augmented by prolongations from the tendons of the semi-membranosus and sartorius muscles, but is separated by a bursa from the tendons of the gracilis, semi-tendinosus, and sartorius. Its deep surface is adherent to the convex edge of the meniscus medialis, but more distally the distal and medial articular vessels intervene between the ligament and the shaft of the tibia.

Lig. Collaterale Fibulare.—The fibular collateral ligament (O.T. external lateral) (Figs. 317 and 318) is a distinct rounded band which is under cover of the ordinary capsule, and yet well separated from the articular cavity by intervening objects. It is attached proximally to the lateral epicondyle, immediately proximal to the groove occupied by the tendon of the popliteus muscle, superficial to which the ligament extends distally to be attached to the lateral side of the head of the fibula, in front of the styloid process. In its course it splits the tendon of insertion of the biceps femoris (Fig. 317), the portions of which are fixed to the head of the fibula on either side of the ligament, and a bursa may intervene between the tendon and the ligament. The distal lateral articular vessels pass forwards subjacent to this ligament and proximal to the head of the fibula. Unlike the tibial collateral ligament, it is not attached to the corresponding meniscus.

The ligamentum laterale externum breve seu posterius (Fig. 317) is an inconstant structure which is attached by its proximal end immediately behind the preceding, and subjacent to the lateral head of the gastrocnemius muscle. It likewise passes superficial to the popliteal tendon, and is affixed distally to the apex capituli of the fibula.

The intra-articular structures of the knee-joint are more important and more numerous than in any other joint of the body.

Ligamenta Cruciata Genu.—The cruciate ligaments (O.T. crucial ligaments) are two strong, rounded, tendinous bands, which extend from the non-articular area

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FIG. 319.—THE KNEE-JOINT OPENED FROM BEHIND BY THE REMOVAL OF THE POSTERIOR LIGAMENT.

on the proximal surface of the head of the tibia to the non-articular sides of the intercondyloid notch of the femur. These interarticular ligaments are distinguished from each other as the anterior or lateral and the posterior or medial. They cross each other like the limbs of an X, yet they remain distinct throughout, and each has its own partial synovial covering. They lie within the articular capsule, and extend between non-articular surfaces in relation to the longitudinal axis of the limb.

The ligamentum cruciatum anterius (Figs. 317, 319, and 320) is attached distally to the medial part of the rough, depressed area in front of and close to the intercondyloid eminence of the tibia. It passes obliquely proximally, laterally, and backwards to the medial non-articular surface of the lateral condyle, where it finds attachment far back in the posterior part of the intercondyloid notch. This

Anterior cornu of
lateral meniscus

ligament is tense in the position of extension, and therefore it assists in maintaining the erect attitude.

The ligamentum cruciatum posterius (Figs. 317, 319, and 320) is somewhat shorter than the preceding. It is attached distally to the posterior part of the depressed surface behind the intercondyloid eminence of the tibia and close to the popliteal notch. Its fibres pass obliquely proximally, forwards, and medially, to be inserted into the lateral non-articular surface of the medial condyle, far forwards towards the anterior margin of the intercondyloid notch. It is rendered tense in the position of flexion.

The semilunar menisci are two in number- a medial and a lateral-placed horizontally between the articular surfaces of the femur and tibia. In general outline they correspond to the circumferential portions of the tibial facets upon which they rest. Each has a thick, convex, fixed border in relation to the periphery of the joint, and a thin, concave, free border directed towards the interior of the joint. Neither of them is sufficiently large to cover the whole of the tibial articular surface upon which it rests.

Transverse ligament The proximal

Anterior cornu of medial

meniscus and distal surfaces of each

Lateral meniscus are Anterior

meniscus smooth and cruciate

ligament free, and each terminates in Medial

Lateral an anterior and inter.

intercondyloid

condyloid a posterior tubercle

tubercle fibrous horn or cornu.

Medial
Meniscus meniscus
Medialis.-
The medial
meniscus (O.T.

Posterior cornu of
Posterior cornu

lateral meniscus internal semi- meniscus

Fasciculus from lateral meniscus

Posterior cruciate ligament to posterior cruciate ligament lunar fibro-carti

FIG. 320.–PROXIMAL END OF Tibia with MENISCI AND ATTACHED PORTIONS OF lage) (Figs. 319

CRUCIATE LIGAMENTS. and 320) forms very nearly a semicircle. It is attached by its anterior horn to the non-articular surface on the head of the tibia, in front of the tibial attaehment of the anterior cruciate ligament, and by its posterior horn to the non-articular surface immediately in front of the tibial attachment of the posterior cruciate ligament. The deep or posterior part of the tibial collateral ligament is attached to its periphery.

Meniscus Lateralis.—The lateral meniscus (Ó.T. external semilunar fibrocartilage) (Figs. 319 and 320) is attached by its anterior horn to the non-articular surface of the tibia in front of the intercondyloid eminence, where it is placed to the lateral side, and partly under cover of the tibial end of the anterior cruciate ligament. By its posterior horn it is attached to the interval between the two tubercles which surmount the intercondyloid eminence, i.e. in front of the attachment of the posterior horn of the meniscus medialis. This fibro-cartilage, with its two horns, therefore forms almost a complete circle. Posteriorly it is attached by its periphery to the posterior ligament, but on the lateral side it is separated from the fibular collateral ligament by the tendon of the popliteus muscle, and on this aspect its periphery is free.

The two horns of the lateral meniscus are embraced by the two horns of the medial meniscus, and, while the anterior cruciate ligament has its tibial attachment almost between the anterior horns of the two menisci, the tibial attachment of the posterior cruciate ligament is situated behind the posterior horns of the two menisci.

Both menisci possess certain accessory attachments. Thus the lateral meniscus sends a large bundle of fibres from its convex posterior border to augment the posterior aspect of the posterior cruciate ligament by which these fibres are

[graphic]

conducted to the femur. Again, the convex or peripheral margins of each meniscus possess certain attachments to the deep surface of the fibrous stratum of the capsule on its medial and posterior aspects, as has already been explained, but, in addition, they are attached to the non-articular circumference of the tibial head by short fibrous bands known as the ligamenta coronaria. Lastly, a rounded band which varies in strength, the lig. transversum genu (transverse ligament) (Figs. 317 and 320), stretches between the anterior convex margins of the two menisci, crossing the front part of the non-articular area on the tibial head in its course.

The stratum synoviale of the knee-joint is not only the largest, but the most elaborately arranged of its kind in the body. It not only lines the fibrous stratum of the capsule articularis, but it forms a more or less extensive covering for the intracapsular ligaments and the free surface of the infra-patellar pad of fat. This pad acts as a wedge which fits into the interval between the patella, tibia, and femoral condyles, and the synovial stratum upon its surface forms a band or fold which extends from the region distal to the level of the patellar articular surface to the anterior part of the intercondyloid notch. It is named the plica synovialis patellaris. At its femoral end it is narrow and attenuated, but at its patellar end it expands on each side to form wing-like fringes or membranes—the plicæ alares-medial and lateral. These folds are more or less loaded with fat.

Apart from these special foldings, the synovial stratum lines the deep surface of the common extensor tendon, and extends for a variable distance proximal to the patella. This extension of the articular cavity almost always communicates with a large bursa situated still more proximally on the front of the femur. Tracing the synovial stratum distally, it will be found to cover both surfaces of the two menisci. The peripheral or convex margins of these menisci are only covered by this membrane where they are unattached to the capsule. A prolongation invests the intracapsular portion of the tendon of the popliteus muscle, and separates this tendon from the posterior part of the tibial head, besides intervening between the lateral meniscus and the head of the tibia.

From the posterior part of the articular cavity the synovial stratum extends forwards, and provides a partial covering for the cruciate ligaments between which a bursa be found.

This somewhat complicated arrangement of the synovial stratum may be readily comprehended if it is borne in mind that it really represents the fusion of three separate synovial cavities, which in some animals are permanently distinct. These are indicated in the two femoro-tibial and the single femoro-patellar parts of the articulation.

The articular cavity may communicate with bursæ situated in relation to the medial head of the gastrocnemius muscle and the tendon of the semi-membranosus muscle, besides the large supra-patellar bursa already described. Lastly, there may be intercommunication between this articular cavity and that of the proximal tibio-fibular articulation.

may

Movements at the Knee-Joint.-In studying the movements which may occur at the human knee-joint, it is necessary to bear in mind that the lower limb of man is primarily required for purposes of support and locomotion. The principal requirement of the former function is stability accompanied by rigidity, whereas in the latter function the special desideratum is regulated and controlled mobility. Thus, in the same joint, two entirely opposite conditions have to be provided. The stable conditions of support are chiefly concerned in the maintenance of the erect attitude, and the mechanism associated therewith does not call for the exertion of a large degree of sustained muscular effort.

In standing erect the attitude of the limb is that of extension, which mainly concerns the femoro-tibial parts of the joint. In this position the force of gravity acts along a vertical line which falls in front of the transverse axis of the joint, and therefore any tendency to flexion, i.e. bending backwards, is mechanically counteracted by the application of a force which tends to produce bending forwards (so-called over-extension). This, however, is absolutely prohibited in normal states of the joint, by the tension of the posterior and collateral ligaments aided by the anterior cruciate ligament. The value of this fact may be seen by observing the effect produced by giving the joint a sudden push from behind, which causes an immediate reversal of the positions of the transverse and vertical axes, whereby the body weight at once produces flexion of the joint.

The menisci and the infra-patellar pad of fat also assist in maintaining extension, by senon of their close adaptation to, and packing round the condyles as these rest upon the tibia.

The anterior margin of the intercondyloid fossa is also brought into contact with the front of the anterior cruciate ligament.

In the position of extension the patella is retained at such a proximal level in relation to the trochlear surface of the femur, that the distal articular facets of the patella are in contact with the trochlea.

During locomotion the movements of the knee-joint are somewhat intricate, for both the femoro-tibial and the femoro-patellar sections of the joint are brought into action. The principal movement which results is flexion, with which there is associated, both at its beginning and ending, a certain amount of screw movement or rotation. Flexion and rotation occur at the femoro-tibial sections of the joint, whereas the movement at the femoro-patellar portion produces a regulating and controlling influence upon flexion.

Taking these factors separately, we observe that each femoral condyle adapts itself to a shallow cup formed by the corresponding tibial condyle and meniscus, and as the two femoral condyles move simultaneously and parallel to each other, there is more than the characteristic hinge-joint action, for each femoral condyle glides and rolls in its cup “like a wheel restrained by a drag” (Goodsir) when the movement of bending occurs. Thus the different parts of the condyles are successively brought into relation with the transverse axis of the joint while it passes from extension to flexion and vice versa. From the fact that the medial femoral condyle is longer than the lateral, it is believed that extension is completed by a movement of rotation whereby the joint becomes locked, and the anterior cruciate, the posterior and the collateral ligaments, become tense. A similar rotation initiates the movement of flexion, and unlocks the joint by relaxing the ligaments just mentioned.

Since the tibia and foot are fixed in the act of walking, it is the femur which rotates upon the tibia in passing from extension to flexion and vice versa ; and as relaxation of the ilio-femoral ligament is essential for this rotation, some observers are of opinion that the body weight falls behind the transverse axis of the knee-joint, as in the case of the hip-joint, and consequently that extension of the knee-joint is maintained by the ilio-femoral ligament, as it is not possible to bend the knee without first having bent the hip-joint.

During flexion and extension the menisci glide along with the condyles, so as to maintain their close adaptation and preserve their value as packing agents. When the movement of flexion is completed, the condyles are retained upon the tibia, and prevented from slipping off by the tension of the posterior cruciate ligament. In this position a small degree of rotation of the tibia, both medially and laterally, is also permissible.

The regulating and controlling influence of the femoro-patellar portion of the articulation is brought into play during the movements of flexion and extension. In the latter position the distal pair of patellar facets is in apposition with the proximal part of the femoral trochlea. As flexion advances, the middle pair of facets adapt themselves to a deeper area of the trochlea, into which the patellar keel fits. When flexion is still further advanced, the proximal pair of patellar facets will be found fitting into that part of the trochlea adjoining the intercondyloid notch; and finally, when flexion is complete, the patella lies opposite the intercondyloid notch, while the forward thrust of the longer medial femoral condyle brings its semilunar facet (Goodsir) into apposition with the somewhat vertical facet at the medial border of the patella. The wedge-like influence of the patella is most marked, for it is only in the position of extension that it be moved from side to side. The movements of the patella may be described as gliding and Co-aptation, as it slips or rocks from one pair of facets to another in its progress along the trough of the femoral trochlea.

ARTICULATIONES TIBIOFIBULARES.

The Tibio-Fibular Joints. The proximal and distal ends of the fibula articulate with the tibia. Primarily, the fibula is required to form a strong lateral support for the ankle-joint, and therefore its articulations are so arranged as to provide a certain amount of elasticity without any sacrifice of the rigidity necessary for security. Hence the amount of movement is very small, but what there is enables these joints to be classified as arthrodial diarthroses.

Articulatio Tibiofibularis.—The proximal tibio-fibular joint is formed, on the one hand, by a flat oval or circular facet which is situated upon the postero-lateral aspect of the lateral condyle of the tibia, and is directed distally and posteriorly; on the other hand, by a similar facet on the proximal surface of the head of the fibula in front of the apex capituli.

An articular capsule (Fig. 317) invests the joint, and it may be regarded as holding the articular surfaces in apposition, although certain special bands receive separate designations. Occasionally there is an opening in the stratum fibrosum by which communication is established between the articular cavity and the knee-joint, through the intermediation of the synovial prolongation, subjacent to the tendon of the popliteus muscle.

The proximal epiphyseal line of the fibula is extra-capsular.

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