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Hip-joint (acetabulofemoral joint - AF)

The hip-joint is a ball-and-socket articulation, formed by the reception of the head of the femur into the cup-shaped fossa of the acetabulum. The articular cartilage on the head of the femur, thicker at the center than at the circumference, covers the entire surface with the exception of the small, roughened pit to which the ligament of the head is attached; that on the acetabulum forms an incomplete ring. Within the articular surface there is a circular depression, named the acetabular fossa, devoid of cartilage, but occupied in the recent state by a mass of fat which is covered with the synovial membrane of the joint. The ligaments of the joint are; capsular, pubofemoral, iliofemoral, ligament of the head of the femur, ischiofemoral, acetabular labrum and transverse acetabular.

The capsular ligament (figs. 553, 554) is strong and dense. Above, it is attached to the margin of the acetabulum, 5 or 6 mm. beyond the acetabular labrum; in front, it is attached to the outer margin of the labrum, and, opposite the acetabular notch, to the transverse acetabular ligament and the edge of the obturator foramen. It surrounds the neck of the femur, and is attached in front to the trochanteric line; above, to the base of the neck; behind, to the neck about 1 cm. above the trochanteric crest; below, to the lower part of the neck close to the lesser trochanter. From its attachment to the front of the neck of the femur many of the fibers are reflected upwards along the neck as longitudinal bands, termed retinacula. The capsular ligament is much thicker at the upper and forepart of the joint, where the greatest amount of resistance is required; behind and below, it is thin and only loosely connected to the bone. It consists of two sets of fibers, circular and longitudinal. The circular fibers (zona orbicularis) are most abundant at the lower and back part of the capsule (figs. 551, 552) and form a sling or collar around the neck of the femur. Anteriorly they blend with the deep surface of the iliofemoral ligament, and gain an attachment to the anterior inferior iliac spine. The longitudinal fibers are greatest in amount at the upper and front part of the capsule, where they are reinforced by the iliofemoral ligament. The articular capsule is also strengthened by the pubofemoral and the ischiofemoral ligaments. The external surface of the capsule is rough; covered by numerous muscles, and separated in front from the psoas major and iliacus by a bursa, which communicates sometimes with the cavity of the joint through a circular aperture.

Figure 551

The synovial membrane is very extensive. Commencing at the margin of the cartilaginous surface of the head of the femur, it covers the portion of the neck which is contained within the joint; from the neck it is reflected on the internal surface of the capsular ligament, covers both surfaces of the acetabular labrum, ensheathes the ligament of the head of the femur, and covers the mass of fat contained in the acetabular fossa. The joint-cavity sometimes communicates, through a hole between the vertical band of the iliofemoral ligament and the pubofemoral ligament, with a bursa situated on the deep surfaces of the psoas major and iliacus muscles.

The iliofemoral ligament (fig. 553), triangular in shape and of great strength, lies in front of the joint and is intimately connected with the capsule. Its apex is attached to the lower part of the anterior inferior iliac spine, its base to the trochanteric line of the femur. The medial and lateral parts of the ligament are strong bands, while the central part is relatively thin and weak; the medial band is vertical in direction and is fixed to the lower part of the trochanteric line; the lateral band is oblique and is attached to the tubercle at the upper part of the same line. The iliofemoral ligament is frequently called the Y-shaped ligament, and its lateral band the iliotrochanteric ligament.

The pubofemoral ligament (fig. 553) is triangular in form with its base at the hip-bone, where it is attached to the iliopubic (iliopectineal) eminence, the superior ramus of the os pubis., the obturator crest and obturator membrane; below, it blends with the capsule and with the deep surface of the medial band of the iliofemoral ligament.

The ischiofemoral ligament (fig. 554) has a somewhat spiral disposition on the back of the joint. From its attachment to the ischium below and behind the acetabulum, it is directed upwards and laterally over the back of the neck of the femur. Some of its fibers are continuous with those of the zona orbicularis, others are fixed to the base of the greater trochanter.

Figure 552

The ligament of the head of the femur (ligamentum teres femoris) (fig. 555) is a triangular, somewhat flattened band implanted by its apex on the anterosuperior part of the pit on the head of the femur, its base is attached by two bands, one into each side of the acetabular notch, and between these bony attachments it blends with the transverse ligament. It is ensheathed by synovial membrane, and varies greatly in strength in different subjects; occasionally only its synovial sheath exists, and in rare cases even this is absent. The ligament is made tense when the thigh is semiflexed and then adducted; it is relaxed when the limb is abducted.

The acetabular labrum (glenoidal labrum) (fig. 547) is a fibrocartilaginous rim attached to the margin of the acetabulum, the cavity of which it deepens. It bridges the acetabular notch as the transverse ligament of the acetabulum, and thus forms a complete circle. It is triangular on cross-section; the base is attached to the edge of the acetabulum, and the apex corresponds with the free margin of the labrum; the latter is in-turned so as to constrict the rim of the acetabular cavity, which closely embraces the head of the femur and assists in holding it in its place.

The transverse ligament of the acetabulum (fig. 547) is in reality a portion of the aeetabular labrum, though differing from it in having no cartilage-cells among its fibers. It consists of strong; flattened fibers, which cross the, acetabular notch, and convert it into a foramen, through which vessels and nerves enter the joint.

The muscles in relation with the joint are: in front, the straight head of rectus femoris, the iliacus and the psoas major (separated from the capsule by a bursa) and the pectineus; above, the reflected head of the rectus femoris and the insertion of gluteus minimus, the latter being closely adherent to the capsule; below, the obturator externus and pectineus; behind, the piriformis, gemellus superior, tendon of obturator internus, gemellus inferior, tendon of obturator externus, and quadratus femoris (fig. 556).

Figure 553

The arteries supplying the joint are derived from the obturator, medial circumflex femoral, and superior and inferior gluteal arteries.

The nerves are articular branches from the sacral plexus, the sciatic, obturator, and accessory obturator nerves, a branch from. the nerve to the cluadratus femoris, and a filament from the branch of the femoral nerve supplying the rectus femoris.

Movements.---The movements of the hip-joint consist of flexion, extension, adduction, abduction, circumduction, and rotation.

Figure 554

The length of the neck of the femur and its inclination to the body of the bone have the effect of converting the angular movements of flexion, extension, adduction, and abduction partially into rotatory movements in the joint. Thus when the thigh is flexed or extended, the head of the femur rotates within the acetabulum around a transverse axis. Rotation of the thigh is not a simple rotation of the head of the femur in the acetabulum, but is accompanied by a certain amount of gliding. The axis of the movement is a vertical line which passes through the center of the head of the femur and the intercondylar notch.

Figure 555

The hip-joint presents a very striking contrast to the shoulder-joint as regards mechanical arrangements for its security and for the limitation of its movements. In the shoulder, as has been seen, the head of the humerus is not adapted at all in size to the glenoid cavity, and is hardly restrained in any of its ordinary movements by the capsule. In the hip-joint, on the contrary, the head of the femur is closely fitted to the acetabulum for an area extending over nearly half a sphere, and at the margin of the bony cup it is still more closely embraced by the acetabular labrum, so that the head of the femur is held in its place by that ligament even when the fibers of the capsule have been quite divided.

Figure 556

The iliofemoral ligament is the strongest of all the ligaments in the body, and is put on the stretch by any attempt to extend the femur beyond a straight line with the trunk. That is to say, this ligament is the chief agent in maintaining the erect position without muscular fatigue; for a vertical line passing through the center of gravity of the trunk falls behind the centers of rotation in the hip-joints, and therefore the pelvis tends to fall backwards, but is prevented mainly by the tension of the iliofemoral ligaments. When the knee is flexed, flexion of the hip-joint is arrested by the soft parts of the thigh and abdomen being brought into contact, and when the knee is extended, by the tension of the hamstring muscles; extension is checked by the tension of the iliofemoral ligament; adduction by the thighs conning into contact; adduction with flexion by the lateral band of the iliofemoral ligament, the lateral part of the capsule and the ligament of the bead of the femur; abduction by the medial band of the iliofemoral ligament and the pubofemoral ligament; lateral rotation by the lateral band of the iliofemoral ligament; medial rotation by the ischiofemoral ligament and the hinder part of the capsule.

Muscles producing the movements:

• Flexion.-Psoas major, lliacus, Pectineus, Rectus femoris, Sartorius, Adductores.
• Extension.---Gluteus maximus, Biceps femoris, Semitendinosus, Semimembranosus.
• Abduction.-Glutei medius et minimus, Sartorius, Tensor fascia latae.
• Adduction.---Adductores, Pectineus, Gracilis.
• Medial rotation.-Glutei medius et mimmus (anterior fibers), Tensor fasciae latae.
• Lateral rotation.-Piriformis, Obturatores, Gemelli, Quadratus femoris, Adductores, Sartorius.

Applied Anatomy.-In dislocation of the hip," the head of the thigh-bone may rest at any point around its socket " (Bryant); but whatever position it assumes ultimately, the primary displacement is generally downwards and medially, the capsule giving way at its weakest-that is, its lower and medial part. The situation subsequently assumed by the head of the bone is determined by the degree of flexion or extension, and of lateral or medial rotation of the thigh at the moment of dislocation, influenced, no doubt, by the iliofemoral ligament, which is not easily ruptured.

The iliofemoral ligament is rarely torn in dislocations of the hip, and this fact is taken advantage of by the surgeon in reducing these dislocations by manipulation. It is made to act as the fulcrum to a lever, of which the long arm is the body of the femur, and the short arm the neck of the bone.

Congenital dislocation is met with more commonly in the hip-joint than in any other articulation. The displacement usually takes place on to the dorsum ilii. It gives rise to extreme lordosis, in order to throw the weight of the body backwards.

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