MRI Anatomy Flashcards · MSK

Bony Pelvis Anatomy

Learn to identify every labeled structure on a Bony Pelvis MRI, plane by plane.

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Bony Pelvis anatomy, structure by structure

Bony pelvis and hip MRI is a workhorse study for hip pain, stress injuries, and sacroiliac disease, and reading it starts with knowing the normal bony and muscular anatomy cold. This reference walks through every structure in our bony pelvis flashcard deck on the coronal plane, with a plain-language definition, how each structure looks on MRI, and the pathology you will actually run into at the scanner.

Pelvic bones

The bony ring of the pelvis: the paired hip bones (ilium, pubis, ischium) and the sacrum that wedges between them at the sacroiliac joints. On coronal images you compare right and left side by side.

Iliac Crest

The curved upper rim of the ilium that you can feel as the top of the hip; a major attachment site for abdominal and gluteal muscles.

On MRI: Sits at the most superior aspect of the pelvic bones on coronal images, with a bright fatty-marrow signal on T1 capped by a thin dark cortical line. It is the highest bony landmark before the soft tissues of the flank.

Common pathology: Apophyseal avulsion injuries in adolescent athletes, marrow signal change from infiltrative disease, and the standard donor site for bone marrow and bone graft harvest.

Tip: Scroll to the top of the coronal stack: the topmost curved bony rim with fatty marrow is the iliac crest.

Ilium

The large, fan-shaped upper portion of the hip bone that forms the bulk of the pelvic sidewall and the upper part of the acetabulum.

On MRI: Forms the broad wing of bone lateral to the sacroiliac joint on coronal images, with bright fatty marrow on T1 outlined by a dark cortex. It blends inferiorly into the acetabular roof.

Common pathology: Stress fractures, metastatic and marrow-replacing lesions, and reactive marrow edema adjacent to sacroiliitis.

Pubis

The anterior-inferior part of the hip bone; the two pubic bones meet in the midline at the pubic symphysis.

On MRI: Seen at the inferior, medial aspect of the pelvis on coronal images, framing the symphysis. Normal marrow is fatty (bright on T1); the symphysis itself is a thin fibrocartilage gap.

Common pathology: Osteitis pubis and athletic pubalgia (bright T2/STIR marrow edema around the symphysis), insufficiency fractures, and parasymphyseal stress injury in runners.

Ischium

The posterior-inferior part of the hip bone that bears weight when seated; the ischial tuberosity anchors the hamstring tendons.

On MRI: Appears at the inferior aspect of the pelvis on coronal images, below the acetabulum. The ischial tuberosity is the rounded bony prominence where the hamstrings attach.

Common pathology: Hamstring origin tendinopathy and avulsion at the ischial tuberosity, ischial bursitis, and insufficiency fractures.

Sacrum

The triangular bone formed by fused vertebrae at the base of the spine that wedges between the two iliac bones to complete the pelvic ring.

On MRI: Occupies the midline at the back of the pelvis on coronal images, flanked by the sacroiliac joints. Fatty marrow is bright on T1; the neural foramina and S1-S2 segments are useful landmarks.

Common pathology: Sacral insufficiency fractures (the classic H-shaped Honda-sign STIR edema across both alae and the central sacrum in older or osteoporotic patients), sacral chordoma, and metastatic disease.

Sacroiliac Joint

The paired joint between the sacrum and each ilium that transfers load from the spine to the legs; it is part synovial and part fibrous.

On MRI: A thin oblique cleft between the sacrum and ilium on coronal images. Dedicated SI joint protocols add oblique coronal and axial fluid-sensitive (STIR or fat-saturated T2) sequences to assess the joint and adjacent marrow.

Common pathology: Sacroiliitis is the key indication: bone marrow edema, erosions, sclerosis, and ankylosis in axial spondyloarthritis. Also degenerative change and infection (pyogenic sacroiliitis).

Tip: When the order says sacroiliitis or spondyloarthritis, angle a fluid-sensitive sequence along the joint plane; marrow edema on both sides of the cleft is what the radiologist is looking for.

Proximal femur

The top of the thigh bone and its landmarks at the hip joint. On coronal images the femoral head sits in the acetabulum and the trochanter projects laterally.

Femoral Head

The rounded ball at the top of the femur that articulates with the acetabulum to form the hip joint.

On MRI: A smooth sphere of bone seated in the acetabulum on coronal images, with bright fatty marrow on T1 under a thin dark cortical and articular cartilage line. The fovea is the small notch for the ligamentum teres.

Common pathology: Avascular necrosis (classic subchondral serpentine or double-line sign), subchondral insufficiency fracture, and femoral head contusion or fracture.

Tip: AVN screening relies on T1 and fluid-sensitive coronals through both femoral heads; compare sides for the early serpiginous line.

Femur

The thigh bone; its proximal shaft and neck connect the femoral head and trochanters to the rest of the leg.

On MRI: The long bone extending inferiorly from the femoral head and neck on coronal images, with bright fatty marrow on T1 and a thick dark cortex. The femoral neck is a common review point.

Common pathology: Femoral neck stress and insufficiency fractures, proximal femoral metastases, and marrow-replacing processes.

Greater Trochanter

The large bony bump on the outer proximal femur that serves as the attachment point for the gluteus medius and minimus tendons.

On MRI: Projects laterally from the proximal femur on coronal images, just below and lateral to the femoral neck. Fatty marrow is bright on T1; look for the tendon footprints on its facets.

Common pathology: Greater trochanteric pain syndrome: gluteus medius/minimus tendinopathy or tears and trochanteric bursitis, with bright T2/STIR fluid lateral to the trochanter.

Gluteal and thigh muscles

The lateral hip abductors and the upper thigh muscle that anchor to the proximal femur. Muscle is intermediate signal on T1 and T2; injury shows up as bright fluid on STIR.

Gluteus Medius

A broad fan-shaped hip abductor that runs from the outer ilium to the greater trochanter and stabilizes the pelvis during walking.

On MRI: The larger, more superficial of the lateral abductors on coronal images, overlying the gluteus minimus and inserting onto the greater trochanter. Normal muscle is intermediate signal with a feathered tendon at the trochanter.

Common pathology: Gluteus medius tendinopathy and tears (the so-called rotator cuff of the hip), a frequent cause of lateral hip pain and trochanteric pain syndrome.

Tip: On coronal images the gluteus medius is the outer abductor layer; the smaller minimus lies deep to it, both converging on the greater trochanter.

Gluteus Minimus

The smallest, deepest gluteal muscle that runs from the outer ilium to the greater trochanter and assists hip abduction and internal rotation.

On MRI: The deep abductor layer on coronal images, lying immediately beneath the gluteus medius and inserting on the anterior facet of the greater trochanter. Intermediate muscle signal on all sequences.

Common pathology: Gluteus minimus tendinopathy and tears, often coexisting with medius pathology in greater trochanteric pain syndrome.

Vastus Lateralis Muscle

The large outer head of the quadriceps that originates near the greater trochanter and lateral femur and extends the knee.

On MRI: The bulky muscle along the lateral aspect of the proximal femoral shaft on coronal images, inferior to the greater trochanter. Normal intermediate muscle signal with internal fatty septa.

Common pathology: Muscle strains and tears, denervation or fatty atrophy, and intramuscular hematoma; bright T2/STIR signal marks acute injury.

Frequently asked questions

What structures are seen on a bony pelvis MRI?

A bony pelvis and hip MRI shows the bones of the pelvic ring (iliac crest, ilium, pubis, ischium, and sacrum), the sacroiliac joints, the proximal femur (femoral head, femoral neck and shaft, and greater trochanter), and the surrounding muscles such as the gluteus medius, gluteus minimus, and vastus lateralis. This page labels all 11 structures from the deck with their MRI appearance.

Which plane is best for studying bony pelvis anatomy?

The coronal plane is the best single view for the bony pelvis: it lays out the pelvic ring side by side, shows both femoral heads seated in the acetabula for comparison, and displays the sacroiliac joints and gluteal muscles in one image. Axial and oblique images are added for the sacroiliac joints and for problem-solving specific structures.

What sequences are used for bony pelvis and hip MRI?

A typical protocol pairs a T1-weighted sequence to read marrow and anatomy with a fluid-sensitive sequence (STIR or fat-saturated T2) to detect edema, fractures, and tendon injury. Fatty marrow is bright on T1, while bone marrow edema and joint fluid turn bright on STIR. Dedicated sacroiliac joint studies add oblique coronal and oblique axial fluid-sensitive images.

Why is the sacroiliac joint such an important landmark?

The sacroiliac joint is the key site for sacroiliitis, the imaging hallmark of axial spondyloarthritis. Technologists are often asked to angle a fluid-sensitive sequence along the joint so the radiologist can assess bone marrow edema, erosions, and sclerosis on both the sacral and iliac sides of the joint.

Do I need an account to use these Bony Pelvis MRI flashcards?

No. The interactive flashcards and this full labeled reference are open to use, with no account required to start. Creating an account lets you save your progress across devices and track which packs you have mastered.

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Bony Pelvis Anatomy