The Hip Joint

The Hip Joint •

This is a multilaxial ball and socket type of synovial joint between the head of the femur and the acetabulum of the hip bone.

Articular Surfaces of the Hip Joint • •

The globular head of the femur articulates with the cup-like acetabulum of the hip bone. The wider superior part of the articular surface is the weight bearing area. Thus it is the ilium that bears the weight.

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The rim of the acetabulum is defective inferiorly at the acetabular notch, which is bridged by the transverse acetabular ligament. The head of the femur forms about twothirds of a sphere and is covered with hyaline cartilage, except over the roughened fovea or pit, to which the ligaments of the head of the femur is attached. More than half of the femoral surface is contained within the acetabulum. The articular or lunate surface of the acetabulum is horseshoe-shaped. The acetabulum has a centrally located nonarticular fossa, which is occupied by a fatpad that is covered with synovial membrane. This nonarticular bone is paper thin and translucent.

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The Acetabular Labrum • •

The depth of the acetabulum is increased by this fibrocartilaginous labrum (L. lip). It is attached to the bony rim of the acetabulum and to the transverse acetabular ligament. The labrum deepens the socket for the femoral head and its free thin edge clasps the head beyond the widest diameter. This helps to hold it firmly in the acetabulum (i.e., preventing dislocation)

The Articular Capsule of the Hip Joint •

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The fibrous capsule is strong and dense. Proximally, it is attached to the edge of the acetabulum, just distal to the acetabular labrum, and to the transverse acetabular ligament. Distally, the fibrous capsule is attached to the neck of the femur as follow: anteriorly to the intertrochanteric line and the root of the greater trochanter and posteriorly to the neck proximal to the greater trochanter and posterior to the neck proximal to the intertrochanteric crest. The fibrous capsule forms a cylindrical sleeve that encloses the hip joint and most of the neck of the femur. Most of its fibre take a spiral course from the hip bone to the lateral potion of the intertrochanteric line of the femur, but some deep fibres from an orbicular zone (zona orbicularis) and pass circularly around the neck of the femur. These fibres form a collar around the neck of the femur, which constricts the capsule and helps to hold the femoral head in the acetabulum. Some deep longitudinal fibres of the fibrous capsule form retinacula, which are reflected superiorly along the neck of the femur as longitudinal bands that blend with the periosteum. The retinacula contain blood vessels that supply the head and neck of the femur.

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Four main groups of longitudinal capsular fibres or intrinsic ligaments are given names according to the region of the hip bone which they attach to the femur. These intrinsic ligaments are thickened parts of the fibrous capsule that strengthen the hip joint.

Ligaments of the Hip Joint •

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The Iliofemoral Ligament is a very strong band that covers the anterior aspect of the hip joint. It is Y-shaped and attached proximally to the anterior inferior iliac spine and the acetabular rim. The iliofemoral ligament is attached distally to the intertrochanteric line of the femur. The capsule of the hip joint is taut and the iliofemoral ligament is tense in full extension of the joint. This strong ligament has an important role in preventing overextension of the hip joint during standing (i.e., it helps to maintain the erect posture. It screws the head of the femur into the acetabulum and thereby maintains the integrity of the joint. The Pubofemoral Ligament arises from the pubic part of the acetabular rim and the iliopubic eminence and blends with the medial part of the iliofemoral ligament. It strengthens the inferior and anterior parts of the fibrous capsule of the hip joint. The pubofemoral ligament tightens during extension of the hip joint and becomes tense during abduction. Although it is relatively weak, this ligament tends to prevent overabduction of the thigh at the hip joint.

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The Ishiofemoral Ligament reinforces the fibrous capsule to the hip joint posteriorly. It arises from the ischial portion of the acetabular rim and spiral superolaterally to the neck of the femur, medial to the base of the greater trochanter. Its anatomical construction tends to screw the femoral head medially into the acetabulum during extension of the thigh at the hip joint, thereby preventing hyperextension of it.

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The Ligament of the Head of the Femur is an intracapsular ligament about 3.5 centimetres long, is weak and appears to be of little importance in strengthening the hip joint. Its wide end is attached to the margins of the acetabular notch and to the transverse acetabular ligament, and its narrow end is attached to the fovea or pit in the femur. Usually it contains a small artery to the head of the femur, which is a branch of the obturator artery. The ligament of the head of the femur (LHF) is stretched when the flexed thigh is adducted or laterally rotated. It is located inside the fibrous capsule of the hip joint and is surrounded by a sleeve of synovial membrane.

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Stability of the Hip Joint •

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The hip joint is very strong and stable articulation. It is surrounded by powerful muscles and a dense fibrous capsule, which is strengthened by strong intrinsic ligaments, particularly the iliofemoral ligament, unites the articulating bones. Its stability is largely the result of the adaptation of the articulating surfaces of the acetabulum and the femoral head to each other. Anterior aspect-fewer muscles, strong ligaments. Posterior aspect-stronger muscles, fewer ligaments. Position of weakness is when the hip joint is flexed, adducted and medially rotated.