Sacroiliac Articulation: Types, Characteristics, Function, Movements and Joint Dysfunction

This joint stabilizes the weight of the legs and upper body, is a fundamental unit for the transfer of strength between the legs and torso.

The sacroiliac joint is located in the pelvis, between the back of the hip and the sacrum, connecting the iliac bone located in the pelvis and the lower part of the spine at the level of the hips, the sacrum.

The sacroiliac joint is strengthened with the support of a network of ligaments and muscles, which likewise restrict movement.

A normal sacroiliac joint has a minimal amount of movement, approximately 2-4 mm of displacement in multiple directions.

The nature of the sacroiliac ligaments in women is less hard than in men, since it requires mobility so that the movement necessary for the birth process can be carried out.

Types

The sacroiliac joint located on the front, is classified as a diarthrodial joint , since this is a type of articulation that can move freely.

It is composed of the sacrum and the two hip bones on the back. However, the articulation on the back is not as mobile as on the front.

The bones remain in place due to the ligaments, these ligaments help the sacrum support the weight of the spine and head and ensure the fit of the joint.

The ligaments in the posterior part of the sacroiliac joint are more abundant in the posterior part than in the anterior.

Some of the ligaments on the back are:

The interosseous sacroiliac ligament: It is arranged between the sacrum and the ilium. This ligament maintains the congruence of the joints and is located at the point where the transfer of the greatest load of weight from the spine to the hip and lower extremities occurs.

The posterior sacroiliac ligament: This ligament is presented as a continuation of the interosseous sacroiliac ligament. It is the one that serves as support for the interlocking mechanism in the frontal planes of the bones (Ilium and sacrum); In this way, it helps the sacrum to support the entire weight of the spine.

The iliolumbar ligament: Supports weight transfer and support functions of the sacroiliac interosseous ligaments and posterior sacroiliac ligaments.

The sacrotuberous ligament: This is a large ligament that goes from the sacrum to the ischial tuberosities.

The sacrospinous ligament: This is a ligament smaller than the previous one with the same disposition, but it does not cover both the joint and the sacrotuberous ligament.

The sacrotuberous and sacrospinous ligaments restrict the bending movement of the sacrum.

characteristics

In the adult, the structure of the sacroiliac joint is oblong, with a concave groove in the back and convex in the anterior, the joint has the shape of an ear or a bean.

The sacroiliac joint has two classifications, one type in the anterior part of the joint and the other in the posterior part of the joint.

In the anterior part it is a synovial or diarthrodial joint . This type of articulation is capable of many movements. In the posterior part, the joint is classified as a syndesmosis, which are protective structures against excessive movements.

The superficial contours of the ilium and the sacrum comprising the sacroiliac joint are connected to each other and interlock to form the anterior part of the joint. The integrity of the sacroiliac joint is maintained only by this interlocking mechanism and by the ligaments.

The portions of the gluteus maximus muscles and the piriform muscles cross the sacroiliac joint.

Function

The sacroiliac joint is responsible for supporting the weight of the spine and to distribute this weight in the area between the hip and the foot.

It is responsible for transmitting torsional or rotational forces, from the lower extremity and up to the vertebral column.

The sacroiliac joint also transmits the weight of your spine to the ischial tuberosities, when the person sits down.

Movements

The front part of the sacroiliac joint is classified as a synovial joint, but it only has a small degree of movement.

But although it is a synovial joint, movement is limited due to the high level of support of the joint and the compromise of weight transfer, which requires a lot of stability and a close connection between the sacrum and the ilium.

Therefore, the movements of the sacroiliac joint include:

  • The movement of the hip bones when they lean forward while the fixed sacrum remains, called the anterior innominate inclination.
  • The movement of the hip bones when they lean back while the sacrum remains fixed, called innominate posterior inclination.
  • The movement of a hip bone when it leans forward, bending the other backwards leaving the sacrum fixed. This movement happens when walking and is called antagonistic inclination.
  • When the sacrum flexes, it is called nutation and when the sacrum is extended, it is called contranutation.

Sacroiliac joint dysfunction

Problems of dysfunctionality of the sacroiliac joint are a common origin of low back pain, with additional symptoms such as pain in the thigh, buttocks that can radiate down the sciatic nerve, but rarely radiating to the foot.

It is usually experienced on only one side of the body, but can be experienced on both sides.