Chapter 5. The hybrid hip case study
rim, which is thick and strong above, and serves for the attachment of the glenoidal labrum (cotyloid ligament), which contracts its orifice, and deepens the surface for articulation. It presents below a deep notch, the acetabular notch, which serves for the attachment of the ligamentum teres. The rest of the acetabulum is formed by a curved cartilaginous surface, the lunate surface, for articulation with the head of the femur.
5.2.2 The cartilages of the hip
Two cartilaginous surfaces are present in the hip joint. One covers almost completely the head of the femur - except the fovea capitis where the teres ligament attaches - and is often called femoral head cartilage. It is thick centrally and thin peripherally.
The other, conversely, is thicker peripherally, has a horse-shoe shape and covers the acetabulum, being calledacetabular cartilageorlunate surface. They are opposing surfaces, are regularly and reciprocally curved, and at any given time only two fifths of the femoral head occupies the acetabulum. The labrum mentioned in section 5.2.1 serves to extend the bony acetabulum into a true hemisphere as well as deepening it thus increasing joint stability. See figure 5.5.
5.2.3 The ligaments of the hip
The articular capsule and ligaments work as static stabilizers of the hip joint, especially the iliofemoral ligament, which tightens in extension enabling the hip to assume a stable close packed position; in the other hand, muscles are considered as dynamic stabilizers.
Contrarily of what happens in other joints, the role of ligaments on determining the hip joint motion and range of motion is less significant.
The articular capsule and the other 6 ligaments of hip joint are described bellow.
It is known, however, that these 7 structures are not separated. Actually, they are blended together to compose the complex of the articular capsule. The differences in names and classification are due to functional variations in thickness and orientation of fibers, as we can observe in the figure 5.6.
The articular capsule is strong and dense. Above, it is attached to the margin of the acetabulum 5 to 6 mm beyond the glenoidal labrum behind; but in front, it is attached to the outer margin of the labrum, and, opposite to the notch where the margin of the cavity is deficient, it is connected to the transverse ligament, and by a few fibers to the edge of the obturator foramen (muscle). It surrounds the neck of the femur, with most fibers running in the same direction of the neck axis, and is attached, in front, to the intertrochanteric line; above, to the base of the neck; behind, to the neck, about 1.25 cm above the intertrochanteric crest; below, to the lower part of the neck, close to the lesser trochanter. From its femoral attachment some of the fibers are reflected upward along the neck as longitudinal bands, termed retinacula. The capsule 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 loose. 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, and form a sling or collar around
5.2. The human hip and its structures
Figure 5.4: Acetabular view of the pelvis indicating ligaments and muscles attachments as well as the anatomical landmarks [Gray, 2000].
Chapter 5. The hybrid hip case study
(a) Lateral view of the horseshoe shaped carti-lage of the hip acetabulum (yellowish part) with surrounding labrum (darker grey rim).
(b) Posterior view of the superior extremity of the human right femur. Yellowish part indicates the cartilage cap and reddish parts show liga-ments and muscles attachment areas.
Figure 5.5: The cartilages of the hip joint (adapted from [Haddad et al., 2001]).
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 distinct bands or accessory ligaments, of which the most important is the iliofemoral ligament.
The pubocapsular ligament, also called pubofemoral is attached above to the obturator crest and the superior ramus of the pubis; below, it blends with the capsule and with the deep surface of the vertical band of the iliofemoral ligament. It reinforces the capsule, checks medial rotation and tightens on abduction.
Theiliofemoralligament is a band of great strength that lies in front of the joint; it is intimately connected with the capsule, and serves to strengthen it. With its twisted fibers, it is one of the strongest ligaments in the body. It is attached, above, to the lower part of the anterior inferior iliac spine; below, it divides into two bands, one of which passes downward and is fixed to the lower part of the intertrochanteric line;
the other is directed downward and laterally and is attached to the upper part of the same line. Between the two bands there is a thinner part of the capsule. In some cases there is no division, and the ligament spreads out into a flat triangular band, which is attached to the whole length of the intertrochanteric line. This ligament is frequently called the Y-shaped ligament. Its functions are: checking medial rotation and extension of the femur; prevention of the closed-packed position of the hip checking adduction somewhat; and what is most important, allows one to stand with minimum muscular activity, because the ligament is tightened when the pelvis rolls backwards during standing.
5.2. The human hip and its structures
(a) Right-hip frontal view. (b) Right-hip posterior view.
(c) Left-hip medial view.
Figure 5.6: The hip joint capsule with ligaments [Gray, 2000].
Chapter 5. The hybrid hip case study
The ligament teres femoris is the ligament of the head of the femur. It is a triangular, somewhat flattened band implanted into the antero-superior part of the fovea capitis femoris (see section 5.2.1 and 5.2.2 for reference). Its base is attached by two bands, one into either side of the acetabular notch, and between these bony attachments it blends with the transverse ligament. This ligament is made tense when the thigh is semiflexed and the limb then adducted or rotated outward; it is, on the other hand, relaxed when the limb is abducted. It has, however, little influence as a ligament, its main function being serving as support to transmit blood vessels.
The ischiocapsular (also ischiofemoral) consists of a triangular band of strong fibers, which spring from the ischium below and behind the acetabulum, and blend with the circular fibers of the capsule. It is distally attached to the posterosuperior aspect of the neck of the femur(where the neck meet the greater trochanter). Its function is to check internal rotation and extension of the femur.
The ischiofemoral ligament is attached proximally to the ischium posterior and posteroinferior to the acetabular rim in the superior and lateral directions.
The glenoidal labrum, also called acetabular lip or acetabular rim, is the fibrocartilaginous edge which forms a ring around the circular outer border of the acetabulum and deepens that cavity. At the same time it protects the edge of the bone, and fills up the inequalities of its surface. It bridges over the notch as the transverse ligament, and thus forms a complete circle, which closely surrounds the head of the femur and assists in holding it in its place. It is triangular on section, its base being attached to the margin of the acetabulum, while its opposite edge is free and sharp.
When the angular limits of the joint are reached, the femoral neck can hit the labrum.
In people whom activities involve repetitive or constant extreme postures of the hip, these hits may cause the labrum to become rigid like bone, and after some time, this rigid structure damage the femoral cartilage, causing a pathology known as arthritis.
[Ferguson, 2000] is a complete reference on the biomechanics of the labrum.
Thetransverse acetabular is in reality a portion of the glenoidal 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, forming a bridge over the artery in the ligament of the femoral head through which the nutrient vessels enter in the joint.