Sacroiliac joint | |
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![]() Sacroiliac joint of the male pelvis, posterior view | |
![]() Human female pelvis, anterior view, with sacroiliac joint within red ellipse. | |
Details | |
Identifiers | |
Latin | articulatio sacroiliaca |
MeSH | D012446 |
TA98 | A03.6.03.001 |
TA2 | 1861 |
FMA | 21440 |
Anatomical terminology |
The sacroiliac joint or SI joint (SIJ) is the joint between the sacrum and the ilium bones of the pelvis, which are connected by strong ligaments. In humans, the sacrum supports the spine and is supported in turn by an ilium on each side. The joint is strong, supporting the entire weight of the upper body. It is a synovial plane joint with irregular elevations and depressions that produce interlocking of the two bones. [1] The human body has two sacroiliac joints, one on the left and one on the right, that often match each other but are highly variable from person to person. [1]
Sacroiliac joints are paired C-shaped or L-shaped joints capable of a small amount of movement [2] (2–18 degrees, which is debatable at this time) that are formed between the auricular surfaces of the sacrum and the ilium bones. However, most [3] agree that there are only slight movements occur on these joints, with only 3 degrees range of motion during flexion-extension, followed by 1.5 degrees axial rotation, and 0.8 degrees lateral bending. [4] The joints are covered by two different kinds of cartilage; the sacral surface has hyaline cartilage and the iliac surface has fibrocartilage. [2] The SIJ's stability is maintained mainly through a combination of only some bony structure and very strong intrinsic and extrinsic ligaments. [5] The joint space is usually 0.5 to 4 mm. [6]
Aging changes the characteristics of the sacroiliac joint. [7] The joint's surfaces are flat or planar in early life. Once walking ability is developed, the sacroiliac joint surfaces begin to develop distinct angular orientations and lose their planar or flat topography. [2] They also develop an elevated ridge along the iliac surface and a depression along the sacral surface. [8] The ridge and corresponding depression, along with the very strong ligaments, increase the sacroiliac joints' stability and makes dislocations very rare. The fossae lumbales laterales ("dimples of Venus") correspond to the superficial topography of the sacroiliac joints.
The ligaments of the sacroiliac joint include the following: [2]
The anterior ligament is not much of a ligament at all and in most cases is just a slight thickening of the anterior joint capsule. The anterior ligament is thin and not as well defined as the posterior sacroiliac ligaments.
The posterior sacroiliac (SI) ligaments can be further divided into short (intrinsic) and long (extrinsic). [9] The dorsal interosseous ligaments are very strong ligaments. They are often stronger than bone, such that the pelvis may actually fracture before the ligament tears. The dorsal sacroiliac ligaments include both long and short ligaments. The long dorsal sacroiliac joint ligaments run in an oblique vertical direction while the short (interosseous) runs perpendicular from just behind the articular surfaces of the sacrum to the ilium and functions to keep the sacroiliac joint from distracting or opening. The sacrotuberous and sacrospinous ligaments (also known as the extrinsic sacroiliac joint ligaments) limit the amount the sacrum flexes.
The ligaments of the sacroiliac joint loosen during pregnancy due to the hormone relaxin; this loosening, along with that of the related symphysis pubis, permits the pelvic joints to widen during the birthing process. The long SI ligaments may be palpated in thin persons for pain and compared from one side of the body to the other; however, the reliability and the validity of comparing ligaments for pain have currently not been shown. The interosseous ligaments are very short and run perpendicular from the iliac surface to the sacrum, they keep the auricular surfaces from abducting or opening/distracting.[ citation needed ]
Like most lower extremity joints, one of the SI joints' functions is shock absorption (depending on the amount of available motion at the sacroiliac joint) for the spine, along with the job of torque conversion allowing the transverse rotations that take place in the lower extremity to be transmitted up the spine. The SI joint, like all lower extremity joints, provides a "self-locking" mechanism (where the joint occupies or attains its most congruent position, also called the close pack position) that helps with stability during the push-off phase of walking. [10] The joint locks (or rather becomes close packed) on one side as weight is transferred from one leg to the other, and through the pelvis the body weight is transmitted from the sacrum to the hip bone.
The motions of the sacroiliac joint
The sacroiliac joints like all spinal joints (except the atlanto-axial) are bicondylar joints, meaning that movement of one side corresponds to a correlative movement of the other side.
Sacroiliitis refers to inflammation of one or both sacroiliac joints, and is one cause of low back pain. With sacroiliitis, the individual may experience pain in the low back, buttock or thigh, depending on the amount of inflammation.
Common mechanical problems of the sacroiliac joint are often called sacroiliac joint dysfunction (also termed SI joint dysfunction; SIJD). Sacroiliac joint dysfunction generally refers to pain in the sacroiliac joint region that is caused by abnormal motion in the sacroiliac joint—either too much or too little motion. It typically results in inflammation of the SI joint, or sacroiliitis.
The following are signs and symptoms that may be associated with an SI joint (SIJ) problem:
Sacroiliac joint dysfunction is tested using provocative and nonprovocative maneuvers. Nonprovocative sacroiliac joint examination maneuvers would include Gillet Test, prone knee flexion test, supine long sitting test, standing flexion test, and seated flexion test. There is a lack of evidence that these sacroiliac joint mobility maneuvers detect motion abnormalities. [13] [14]
Given the inherent technical limitations of the visible and palpable signs from these sacroiliac joint mobility maneuvers, another broad category of clinical signs has been described called provocative maneuvers. These maneuvers are designed to reproduce or increase pain originating from within the sacroiliac joint. When the provocative maneuvers reproduce pain along the typical area, it raises suspicion for sacroiliac joint dysfunction. However no single test is very reliable in diagnosing of sacroiliac joint dysfunction. Weakness, numbness, or the loss of a related reflex may indicate nervous system damage.
The current gold standard for diagnosis of sacroiliac joint dysfunction emanating within the joint is sacroiliac joint injection confirmed under fluoroscopy or CT-guidance using a local anesthetic solution. The diagnosis is confirmed when the patient reports a significant change in relief from pain and the diagnostic injection is performed on 2 separate visits. Published studies have used at least a 75 percent change in relief of pain before a response is considered positive and the sacroiliac joint deemed the source of pain. [15] [16] [17]
The hormonal changes of menstruation, pregnancy, and lactation can affect the integrity of the ligament support around the SIJ, which is why women often find the days leading up to their period are when the pain is at its worst. During pregnancy, female hormones are released that allow the connective tissues in the body to relax. The relaxation is necessary so that during delivery, the female pelvis can stretch enough to allow birth. This stretching results in changes to the SIJs, making them overly mobile. Over a period of years, these changes can eventually lead to wear-and-tear arthritis. As would be expected, the more pregnancies a woman has, the higher her chances of SI joint problems. During the pregnancy, micro tears and small gas pockets can appear within the joint.[ citation needed ]
Muscle imbalance, trauma (e.g., falling on the buttock) and hormonal changes can all lead to SIJ dysfunction. Sacroiliac joint pain may be felt anteriorly, however, care must be taken to differentiate this from hip joint pain.
Women are considered more likely to suffer from sacroiliac pain than men, mostly because of structural and hormonal differences between the sexes, but so far no credible evidence exists that confirms this notion. Female anatomy often allows one fewer sacral segment to lock with the pelvis, and this may increase instability.
The leg is the entire lower limb of the human body, including the foot, thigh or sometimes even the hip or buttock region. The major bones of the leg are the femur, tibia, and adjacent fibula. The thigh is between the hip and knee, while the calf (rear) and shin (front) are between the knee and foot.
The coccyx, commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates since Nacholapithecus, the coccyx is the remnant of a vestigial tail. In animals with bony tails, it is known as tailhead or dock, in bird anatomy as tailfan. It comprises three to five separate or fused coccygeal vertebrae below the sacrum, attached to the sacrum by a fibrocartilaginous joint, the sacrococcygeal symphysis, which permits limited movement between the sacrum and the coccyx.
The sacrum, in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1–S5) between ages 18 and 30.
The piriformis muscle is a flat, pyramidally-shaped muscle in the gluteal region of the lower limbs. It is one of the six muscles in the lateral rotator group.
In vertebrate anatomy, the hip, or coxa in medical terminology, refers to either an anatomical region or a joint on the outer (lateral) side of the pelvis.
The external iliac arteries are two major arteries which bifurcate off the common iliac arteries anterior to the sacroiliac joint of the pelvis.
The dimples of Venus are sagittally symmetrical indentations sometimes visible on the human lower back, just superior to the gluteal cleft. They are directly superficial to the two sacroiliac joints, the sites where the sacrum attaches to the ilium of the pelvis. An imaginary line joining both dimples of Venus passes over the spinous process of the second sacral vertebra.
The multifidusmuscle consists of a number of fleshy and tendinous fasciculi, which fill up the groove on either side of the spinous processes of the vertebrae, from the sacrum to the axis. While very thin, the multifidus muscle plays an important role in stabilizing the joints within the spine. The multifidus is one of the transversospinales.
The sacrotuberous ligament is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends.
The superior gluteal artery is the terminal branch of the posterior division of the internal iliac artery. It exits the pelvis through the greater sciatic foramen before splitting into a superficial branch and a deep branch.
The wing(ala)of ilium is the large expanded portion of the ilium, the bone which bounds the greater pelvis laterally. It presents for examination two surfaces—an external and an internal—a crest, and two borders—an anterior and a posterior.
The iliolumbar ligament is a strong ligament which attaches medially to the transverse process of the 5th lumbar vertebra, and laterally to back of the inner lip of the iliac crest.
The interosseous sacroiliac ligament, also known as the axial interosseous ligament, is a ligament of the sacroiliac joint that lies deep to the posterior ligament. It connects the tuberosities of the sacrum and the ilium of the pelvis.
A pelvic fracture is a break of the bony structure of the pelvis. This includes any break of the sacrum, hip bones, or tailbone. Symptoms include pain, particularly with movement. Complications may include internal bleeding, injury to the bladder, or vaginal trauma.
The lumbar fascia is the lumbar portion of the thoracolumbar fascia. It consists of three fascial layers - posterior, middle, and anterior - that enclose two muscular compartments. The anterior and middle layers occur only in the lumbar region, whereas the posterior layer extends superiorly to the inferior part of the neck, and the inferiorly to the dorsal surface of the sacrum. The quadratus lumborum is contained in the anterior muscular compartment, and the erector spinae in the posterior compartment. Psoas major lies anterior to the anterior layer. Various superficial muscles of the posterior thorax and abdomen arise from the posterior layer - namely the latissimus dorsi, and serratus posterior inferior.
The following outline is provided as an overview of and topical guide to human anatomy:
The hip bone is a large flat bone, constricted in the center and expanded above and below. In some vertebrates it is composed of three parts: the ilium, ischium, and the pubis.
The term sacroiliac joint dysfunction refers to abnormal motion in the sacroiliac joint, either too much motion or too little motion, that causes pain in this region.
The pelvis is the lower part of the trunk, between the abdomen and the thighs, together with its embedded skeleton.
The sacroiliac joint is a paired joint in the pelvis that lies between the sacrum and an ilium. Due to its location in the lower back, a dysfunctional sacroiliac joint may cause lower back and/or leg pain. The resulting leg pain can be severe, resembling sciatica or a slipped disc. While nonsurgical treatments are effective for some, others have found that surgery for the dysfunctional sacroiliac joint is the only method to relieve pain.
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