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The posterior superior iliac spine (PSIS) is a crucial pelvic landmark that serves as an attachment point for various muscles and ligaments. It is the most posterior projection of the iliac crest and plays an integral role in identifying pelvic torsion and conducting patient assessment procedures. The PSIS is associated with the sacroiliac (SI) joint, which connects the sacrum and innominate, providing stability and resisting anterior and inferior movements of the sacrum. The SI joint is well-innervated, receiving input from various sources, including the ventral rami of L4 and L5, the superior gluteal nerve, and the dorsal rami of L5-S2. The gluteus maximus, with its complex origin and insertion points, is closely related to the PSIS and contributes to stability during walking. The deep lamina of the thoracolumbar fascia also attaches to the PSIS, along with other structures such as the sacrotuberous ligament, iliac crest, and long dorsal ligament.
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What You'll Learn
- The multifidus muscle inserts at the inferomedial aspect of the PSIS
- The gluteus maximus attaches to the superficial lamina of the thoracolumbar fascia, near the PSIS
- The sacrospinous ligament opposes forward tilting of the sacrum, connecting to the PSIS
- The Fortin finger test assesses pain within 1 cm of the PSIS
- The Gillette test involves palpating the PSIS to assess SI joint motion
The multifidus muscle inserts at the inferomedial aspect of the PSIS
The multifidus muscle is a part of the transversospinalis group and contributes to the third deepest layer of the intrinsic or deep muscles of the back. The rotatores muscles lie directly beneath it, while the semispinalis cervicis and semispinalis thoracis muscles are positioned on its superficial side. The multifidus muscle is also located beneath the erector spinae group, which includes the spinalis, longissimus, and iliocostalis muscles.
The multifidus muscle consists of short and long fibres. The short fibres originate at the posteroinferior vertebral laminae and spinous processes of the vertebral body above and insert at the vertebral mammillary process below. The lowest level of this series originates at the L5 laminar fibres and inserts onto the sacrum superior to the first dorsal sacral foramen. The long fibres from the base of the spinous process of L2 attach caudally to the mammillary process of L5, whereas those of the common tendon insert into the mammillary process of S1 vertebrae, the PSIS of the innominate, and an area on the iliac crest just caudoventral to the PSIS.
The multifidus muscle originates at the lumbar spinous processes and laminae and inserts at the mammillary processes, the inferomedial aspect of the PSIS, the erector spinae aponeurosis, the dorsal aspect of the sacrum to S4, and the dorsal sacroiliac ligaments. The multifidus muscle receives its innervation from the medial branch of the dorsal rami of the same segmental number.
The multifidus muscle plays a crucial role in providing functional stabilization to the vertebral joints. When both sides of the multifidus muscle contract simultaneously (bilateral contraction), it extends the vertebral column, enabling you to straighten your back when standing upright. On the other hand, when the muscle contracts on only one side (unilateral contraction), it facilitates lateral flexion of the spine towards the same side, allowing you to bend your body trunk sideways.
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The gluteus maximus attaches to the superficial lamina of the thoracolumbar fascia, near the PSIS
The gluteus maximus is the body's largest and heaviest muscle. It is the most superficial of all the gluteal muscles, located at the posterior aspect of the hip joint. The muscle fibres take an inferolateral course, converging towards the femur. The gluteus maximus is a powerful extensor of the hip joint, activated during powerful lower limb movements such as stepping onto a step, climbing, or running.
The gluteus maximus muscle originates from several sites, including the thoracolumbar fascia. The thoracolumbar fascia consists of a deep lamina and a superficial lamina. The deep lamina fuses with the aponeurosis of the gluteus medius laterally and, more medially, the deep and superficial laminae fuse together at the level of the PSIS. Below the PSIS, the combined aponeurotic structure extends laterally to create an intermuscular septum to which the gluteus maximus attaches in a bipennate arrangement.
The gluteus maximus attachment to the superficial lamina of the thoracolumbar fascia is between the lower border of the PSIS and a point 1.0-2.0 cm lateral to the S3. The PSIS, or posterior superior iliac spine, is a small bony process that can be located by moving posterior along the iliac crest. The gluteus maximus covers all of the gluteal muscles except for the antero-superior third of the gluteus medius.
The gluteus maximus is supplied by the inferior gluteal nerve (root L5, S1, and S2). It receives its blood supply from the inferior and superior gluteal arteries.
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The sacrospinous ligament opposes forward tilting of the sacrum, connecting to the PSIS
The sacroiliac (SI) joint connects the surfaces of the sacrum and the ilium, acting as a transition between the spine and the pelvis. The sacrospinous ligament is one of the two main accessory ligaments of the sacroiliac joint, the other being the sacrotuberous ligament.
The sacrospinous ligament is triangular in shape and is located deep to the sacrotuberous ligament. It originates on the ischial spine and attaches to the lateral parts of the sacrum and coccyx, opposing the nutation of the sacrum during weight-bearing and gait. The sacrospinous ligament, along with the sacrotuberous ligament, functions to prevent forward tilting of the sacral promontory by anchoring the inferior end of the sacrum to the ischium. This forward tilting of the sacrum is also known as nutation, which is the anterior motion of the sacrum. Counternutation refers to the posterior motion of the sacrum.
The sacroiliac joint is stabilised by a strong ligamentous architecture, with the sacrospinous ligament being an essential component of this structure. The ligament's role in opposing forward tilting of the sacrum helps to maintain the stability of the joint and ensures the proper distribution of force loads from the lower extremities. This force attenuation is one of the primary functions of the sacroiliac joint, acting as a shock absorber for the spine and converting torque from the lower extremities into the rest of the body.
The sacrospinous ligament is also involved in creating the greater and lesser sciatic notches, which, in conjunction with the sacrotuberous ligament, become the greater and lesser sciatic foramina. These ligaments help prevent flexion and rotation of the ilium past the sacrum, further contributing to the stability of the sacroiliac joint.
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The Fortin finger test assesses pain within 1 cm of the PSIS
The Fortin finger test is a clinical assessment used to detect sacroiliac joint dysfunction, which is a condition that affects the sacroiliac (SI) joint, connecting the sacrum (the triangular bone at the bottom of the spine) to the pelvis. This joint can become a source of pain due to various factors, including injury, inflammation, or degeneration. The test helps identify SI joint pain, often associated with lower back and lower limb pain.
During the test, the patient is asked to use one finger to localize the area of pain. The examiner notes the location and then asks the patient to relax. After five to ten minutes, the examiner asks the patient to identify the spot where they feel the most pain once more. A positive test is indicated when the patient twice identifies the painful region as the area within 1 cm inferomedial to the posterior superior iliac spine (PSIS). This consistent localization of pain suggests sacroiliac joint dysfunction.
The Fortin Finger Test template guides professionals through each step of the differential diagnosis, ensuring no critical element is overlooked. This includes taking the patient's medical history, performing a physical examination, and screening using the Fortin Finger Test before moving on to other provocative tests. Accurate patient details are crucial for effectively tracking differential diagnoses and managing their condition.
The test is named after Fortin JD and Falco FJ, who reported excellent interrater reliability in their original 1997 study. The test is beneficial for physical therapists, pain physicians, and chiropractors as it promotes accuracy and completeness in patient records. It is a quick and efficient way to assess patients, allowing more time to focus on patient care and other critical tasks.
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The Gillette test involves palpating the PSIS to assess SI joint motion
The Gillette test, also known as the step test, one-legged stance test, or stork test, is a manual therapy technique used to assess motion at the sacroiliac (SI) joint. The SI joint is supported by the gluteus maximus muscle, which has origins at the ilium, thoracolumbar fascia, and dorsal sacroiliac ligaments, among other attachments. The Gillette test involves palpating the posterior superior iliac spine (PSIS) to evaluate SI joint motion.
During the test, the examiner palpates the inferior aspect of the PSIS on the tested side with one hand while placing the other hand on the S2 spinous process. The patient is instructed to flex the hip past 90 degrees. A positive test result indicates the presence of SI joint motion, as the examiner should feel the PSIS move inferiorly and laterally relative to the sacrum. This motion is due to the structures on the posterior side of the pelvis becoming taut and rotating the inominate in a posterior direction relative to the sacrum.
An alternate method for the Gillette test involves palpating both PSIS areas simultaneously and comparing the end position. This test is used to determine if restrictions are present in the SI joint. If the inominate is unable to move relative to the sacrum, it suggests a restriction in the joint. However, it is important to note that abnormal SI motion can be found in asymptomatic patients, so the Gillette test should not be solely relied upon to determine the origin of a patient's symptoms.
The validity of the Gillette test has been questioned in certain studies. For example, one study found that neither palpator identified fixed SI joints in subjects with ankylosing spondylitis, raising doubts about the test's reliability. Some manual therapists have suggested retooling the test as a qualitative indicator of SI stability rather than a quantitative assessment of SI motion. Additionally, the test should only be performed by a properly trained healthcare practitioner.
In conclusion, the Gillette test is a manual therapy technique that involves palpating the PSIS to assess SI joint motion. While it can provide valuable information about SI joint restrictions, its validity and reliability have been questioned by some studies. Therefore, it should be used in conjunction with other assessment methods and performed by trained individuals to ensure accurate interpretation of the results.
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Frequently asked questions
PSIS stands for Posterior Superior Iliac Spine. It is a pelvic landmark that is important for identifying possible pelvic torsion.
The multifidus muscle attaches to the inferomedial aspect of the PSIS. The gluteus maximus also attaches to the PSIS.
The gluteus maximus provides stability to the SIJ and is involved in walking.
The multifidus muscle provides stability to the SIJ and is involved in respiration.
The PSIS is a reference point for a variety of patient assessment procedures, including the Fortin finger test and the Gillette test, which are used to assess pain and joint motion.
