Capsular and joint architecture

The ilium, ischium, and pubic bones unite at the acetabulum, forming the innominate bone. During childhood, these bones are separated within the ac-etabulum by the triradiate cartilage, which fuses at skeletal maturity.

The acetabulum has an inclined abduction angle of approximately 35 degrees from the horizontal and a forward flexed position of approximately 20 degrees (Figure 6.8A,C). The articular surface of the acetabulum has a horseshoe or lunate shape (Figure 6.9). The central inferior acetabular fossa is devoid of articular surface. It is occupied by a fat pad covered with synovium called the pulvinar. Additionally, it contains the acetabular attachment of the ligamentum teres. The socket of the acetabulum is completed inferiorly by the transverse acetabular ligament.

FIGURE 6.8. (A) Acetabular orientation averages 35 degrees of abduction from the horizontal plane. The neck shaft angle formed between the axis of the femoral neck and femoral shaft averages 125 degrees. (B) Femoral anteversion, determined by the angle created

Angle of Acetabular Forward Flexion between the bicondylar axis of the knee and the axis of the femoral neck in the transverse plane, averages 14 degrees. (C) The acetabu-lum is also oriented with 20 degrees of forward flexion relative to the sagittal plane.

Overweight Femoral Nerve

FIGURE 6.7. Neurovascular structures (posterior view).

Sciatic nerve/ Medial circumflex femoral artery'

FIGURE 6.7. Neurovascular structures (posterior view).

Femur Structure

FIGURE 6.8. (A) Acetabular orientation averages 35 degrees of abduction from the horizontal plane. The neck shaft angle formed between the axis of the femoral neck and femoral shaft averages 125 degrees. (B) Femoral anteversion, determined by the angle created

FIGURE 6.9. Formed from portions of the ilium, ischium, and pubis, the lunate-shaped articular surface of the ac-etabulum surrounds the fossa containing the acetabular attachment of the ligamentum teres and fat, both encased in synovium. The labrum effectively deepens the socket and is contiguous with the transverse acetabular ligament inferiorly. The articular surface of the femoral head forms approximately two-thirds of a sphere. Medially, the liga-mentum teres attaches at the fovea capitis. The diameter of the femoral neck is only 65% of the diameter of the femoral head, which allows for freer range of motion without marginal impingement.

Femoral Attachment The Etabulum

The labrum is a fibrocartilaginous structure that attaches to the bony rim of the acetabulum, effectively deepening to a socket. The labrum terminates inferi-orly at the anterior and posterior margins of the ac-etabular fossa. It then becomes contiguous with the transverse acetabular ligament, which completes the circumferential ring of the acetabulum. We are learning that the labrum is a nonhomogeneous structure with considerable variation in different areas of the acetabulum (see Chapter 8).

Although variable, the proximal femur has a neck shaft angle that averages 125 degrees, with approximately 14 degrees of femoral neck anteversion (see Figure 6.8A,B). The femoral head has an articular surface that forms approximately two-thirds of a sphere, articulating with the acetabulum (see Figure 6.9). Medially, on the articular portion of the femoral head, is a pit called the fovea capitis, the site of the femoral attachments of the ligamentum teres.

The bony architecture of the hip provides it with significant intrinsic stability. This stability is further enhanced by an intricate complex of capsular ligaments. This complex consists of four distinct ligaments that provide varying contributions to the joint.

The intricate nature and specific design of the capsular ligaments has been well defined by various anatomic studies. However, over time, more will be learned about the ligaments as a better appreciation is gained of the arthroscopic appearance of this anatomy. Perhaps this construct will even be partially redefined.

Anteriorly, the capsule consists primarily of the il-iofemoral ligament or ligament of Bigelow (Figure 6.10). It has an inverted Y shape beginning from its iliac attachment on the superior aspect of the acetabu-lum. It then fans out in a spiraling pattern to its femoral attachment along the intertrochanteric line. It is one of the strongest ligaments in the body, and the spiral-ing direction of its fibers makes it taut in extension in a wringing-out mechanism and relaxed in flexion.

The ischiofemoral ligament reinforces the posterior capsule (Figure 6.11). It too has a spiraling pattern as it courses from its ischial attachment on the posterior acetabular rim to its femoral attachment on the superolateral neck, medial to the base of the greater trochanter.

The pubofemoral ligament, although relatively weak, reinforces the inferior and anterior capsule from

Iliofemoral ligament

Pubofemoral ligament

Iliofemoral ligament

Pubofemoral ligament

Femoral Attachment The Etabulum

FIGURE 6.11. The ischiofemoral ligament reinforces the posterior capsule, spiraling from its attachment on the ischial portion of the posterior acetabulum to the superolateral aspect of the femoral neck.

FIGURE 6.10. The iliofemoral ligament (ligament of Bigelow) has the shape of an inverted Y as it spirals from its attachment on the iliac portion of the superior acetabulum to its femoral attachment on the anterior neck. It is quite powerful and becomes taut in extension. The relatively weak pubofemoral ligament reinforces the inferior and anterior capsule, where it blends with the medial edge of the iliofemoral ligament.

FIGURE 6.11. The ischiofemoral ligament reinforces the posterior capsule, spiraling from its attachment on the ischial portion of the posterior acetabulum to the superolateral aspect of the femoral neck.

the pubic part of the acetabular rim where it blends with the medial edge of the iliofemoral ligament (see Figure 6.10). Again, the spiraling nature of this complex tends to screw the femoral head medially into the acetabulum during extension, which has several clinical implications. First, this explains why patients with an irritable hip, whether the result of trauma, disease, or infection, tend to rest with the hip in a slightly flexed position, relaxing the capsule. Second, from a surgical standpoint, it would appear advantageous to perform arthroscopy with the hip flexed, further relaxing the capsule. However, this can create potential concern for portal placement, as discussed in Chapter 7.

The fourth ligament is the ligament of the head of the femur (ligamentum teres) (Figure 6.12). Coursing from its attachment in the acetabular fossa to the fovea of the femoral head, it is intracapsular, yet encased in synovium, making it extrasynovial. Its relatively weak, redundant nature makes it unlikely that this has any significant stabilizing effect on the hip. The size and strength of this ligament are variable, and it is occasionally absent, the significance of which is unknown.

A deep layer of fibers within the ligamentous capsule courses circularly around the neck of the femur, creating the zona orbicularis (see Figure 6.12). This layer may serve as a collar to constrict the capsule and help maintain the femoral head within the acetabulum.

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Responses

  • cora
    Where does the capsuale attach on femoral neck?
    3 years ago
  • billy shaw
    What joint is femoral head?
    7 months ago

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