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Ramus of ischium

The ramus of the ischium is a strong, flattened extension of the ischial body that projects anteromedially to unite with the inferior ramus of the pubis, forming the ischiopubic ramus. Together, these structures contribute to the inferior border of the obturator foramen and the anterior part of the pelvic outlet.

The ramus provides important muscular and ligamentous attachments. The adductor magnus and gracilis muscles originate from the ischiopubic ramus, while the obturator externus arises from the adjacent margin. It also provides attachment for the perineal muscles and ischiocavernosus muscle. Ligamentous connections include portions of the obturator membrane and pelvic fascia.

Clinically, the ramus of the ischium is relevant in pelvic trauma (fractures and avulsions), pelvic tumor invasion, osteomyelitis, congenital malformations, and surgical procedures involving the urogenital diaphragm and pelvic floor.

Synonyms

  • Ischial ramus

  • Inferior ramus of ischium

  • Ischiopubic ramus (when combined with pubic ramus)

Function

  • Contributes to the structural stability of the pelvis

  • Forms part of the obturator foramen and pelvic outlet

  • Provides muscular origin for adductor magnus, gracilis, and obturator externus

  • Provides attachment to pelvic floor and perineal muscles

  • Serves as an anchor point for ligamentous and fascial structures

Nerve Supply (related muscles)

  • Adductor magnus: obturator nerve (posterior branch) and tibial part of sciatic nerve

  • Gracilis: obturator nerve (anterior branch)

  • Obturator externus: obturator nerve

Arterial Supply

  • Branches of the obturator artery

  • Contributions from the inferior gluteal artery and internal pudendal artery

Venous Drainage

  • Obturator vein → internal iliac vein

  • Internal pudendal venous plexus

MRI Appearance

T1-weighted images:

  • Bone cortex: dark hypointense outline

  • Bone marrow: intermediate signal, fatty marrow more hyperintense in adults

  • Useful for detecting fractures, marrow infiltration, or tumor extension

T2-weighted images:

  • Cortex: hypointense

  • Marrow: variable signal; edema or tumor infiltration appears hyperintense

  • Helps evaluate periosteal reactions or marrow abnormalities

PD Fat-Saturated:

  • Cortex: hypointense

  • Bone marrow edema: bright hyperintense signal

  • Very sensitive for stress fractures, early trauma, or enthesopathy

STIR:

  • Suppresses fat, making marrow edema, infection, or trauma highly conspicuous as hyperintense regions

  • Useful in osteomyelitis or stress-related injuries

T1 Post-Gadolinium (fat-saturated):

  • Normal bone marrow: mild uniform enhancement

  • Pathological processes (tumors, infections, inflammatory changes): show intense or heterogeneous enhancement

  • Outlines soft-tissue masses spreading from the ischiopubic ramus

3D T2-weighted Imaging:

  • Cortex: sharply hypointense

  • Provides isotropic data for multiplanar reconstructions

  • Useful for preoperative planning in pelvic surgery, trauma, and tumor evaluation

CT Appearance

Non-contrast CT:

  • Bone cortex: hyperdense with sharp definition

  • Marrow: lower density than cortex

  • Excellent for evaluating fractures, cortical irregularities, lytic lesions, or sclerotic changes

CT Post-Contrast:

  • Bone: unchanged

  • Surrounding soft tissues: enhance if inflamed or infiltrated by tumor

  • Useful for osteomyelitis, abscesses, and tumor extension

  • 3D reconstructions provide clear visualization of ischiopubic ramus anatomy for surgical planning

Clinical Significance

  • Fractures: occur in pelvic trauma, often associated with pubic rami fractures

  • Avulsion injuries: in adolescents at muscle attachment sites (gracilis, adductor magnus)

  • Osteomyelitis: presents as marrow edema on MRI, lytic areas on CT

  • Oncology: common site for tumor extension in pelvic malignancies

  • Surgical landmark: important in urogenital surgery and pelvic floor reconstruction

CT VRT 3D image

Ramus of ischium 3D CT VRT anatomy image

CT image

Ramus of ischium ct axial

MRI image

Ramus of ischium MRI axial anatomy image-img-00000-00000