Posterior inferior iliac spine

Posterior Inferior Iliac Spine

The posterior inferior iliac spine (PIIS) is a bony prominence located on the posterior aspect of the ilium, which is one of the three bones that make up the hip bone or pelvic girdle. It serves as an important attachment site for various muscles and ligaments involved in the movement and stability of the hip joint.

Anatomy

The PIIS is a small, pointed projection that extends posteriorly and inferiorly from the posterior border of the ilium. It is situated just below the larger and more prominent posterior superior iliac spine (PSIS). The PIIS can be palpated by placing the hand on the back of the hip and moving it downward and inward towards the midline.

Function

The PIIS serves as an attachment site for several muscles and ligaments, playing a crucial role in the stability and movement of the hip joint. Some of the important structures that attach to the PIIS include:

1. **Sacrospinous ligament**: This ligament originates from the PIIS and attaches to the sacrum. It helps to stabilize the sacroiliac joint, which is the joint between the sacrum and the ilium.

2. **Obturator internus muscle**: This muscle arises from the inner surface of the obturator membrane and the surrounding bony margins. It passes through the lesser sciatic foramen and attaches to the PIIS. The obturator internus muscle is responsible for the external rotation of the hip joint.

3. **Gemellus inferior muscle**: This muscle arises from the ischial tuberosity, passes through the lesser sciatic foramen, and attaches to the PIIS. It works in conjunction with the obturator internus muscle to assist in the external rotation of the hip joint.

4. **Quadratus femoris muscle**: This muscle originates from the ischial tuberosity and attaches to the PIIS. It is involved in the lateral rotation of the hip joint.

Clinical Significance

The PIIS can be a site of pain and discomfort in certain conditions. Inflammation or strain of the muscles and ligaments attached to the PIIS can result in posterior hip pain. This can occur due to overuse, trauma, or underlying conditions such as tendinitis or bursitis.

In addition, the PIIS can be used as a landmark for various clinical procedures. For example, during a sacroiliac joint injection, the PIIS can be palpated to locate the appropriate site for the injection. It can also be used as a reference point for identifying other anatomical structures in the pelvic region.

References

1. Standring, S. (Ed.). (2016). Gray's Anatomy: The Anatomical Basis of Clinical Practice (41st ed.). Elsevier.

2. Drake, R. L., Vogl, W., & Mitchell, A. W. M. (2014). Gray's Anatomy for Students (3rd ed.). Elsevier.

See Also

• Ilium
• Posterior Superior Iliac Spine
• Hip Joint
• Sacroiliac Joint