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Joints of the Pelvic Bones

Articulationes cinguli pelvici

For medical students2 min readUpdated 2026-10-10

The bones of the lower limb form a strong pelvic ring through a system of continuous and discontinuous articulations. The main structures of this framework are the semi-mobile pubic symphysis anteriorly and the paired sacroiliac joints posteriorly, reinforced by a powerful ligamentous apparatus.

Articular surfacesRepresented by the auricular surfaces of the sacrum and the ilium
Pubic symphysisIncludes a fibrocartilaginous disc, which may contain a slit-like cavity internally
MobilityThe sacroiliac articulation is an amphiarthrosis (a slightly movable joint)

Pubic Symphysis

Anteriorly, the pelvic ring is closed by the pubic symphysis (symphysis pubica). This junction represents a transitional form between a continuous articulation and a true joint.

The main structural feature of the symphysis is the presence of a specialized fibrocartilaginous disc located between the articulating surfaces of the pubic bones. A small slit-like cavity may occasionally form within the substance of this cartilaginous disc.

To ensure mechanical stability, the pubic symphysis is additionally reinforced by a ligamentous apparatus:

Sacroiliac Joints

The posterior part of the pelvic ring is formed by the paired sacroiliac joints (articulationes sacroiliacae).

Specific articular facets—the auricular surfaces—located on the lateral masses of the sacrum and corresponding regions of the ilium take part in forming this joint. According to its biomechanical classification, this joint is plane. Functionally, it is an amphiarthrosis (a slightly movable articulation), which is critically important for the stability of the entire pelvic ring during weight transmission.

The joint capsule here is very strong and tightly stretched. The robust stabilizing apparatus of the sacroiliac joint includes the following ligaments:

  1. Internal joint ligaments: anterior, interosseous, and posterior sacroiliac ligaments (ligg. sacroiliaca ventralia, dorsalia et interossea).
  2. Additional fixation is provided by the iliolumbar ligament (lig. iliolumbale).

Ligaments Forming the Sciatic Foramina

In addition to the ligaments that directly reinforce the joints, large fibrous bands with critical topographical roles are located in the region of the pelvic ring.

These include:

These two powerful ligaments span between the bony structures of the pelvis and bridge the bone notches, converting them into the greater and lesser sciatic foramina. Important neurovascular bundles and muscles subsequently pass through these foramina.

Mnemonic

To remember the ligaments of the sacroiliac joint, orient yourself by planes: anterior (ventral), posterior (dorsal), and internal (interosseous) — ligg. sacroiliaca ventralia, dorsalia et interossea.

Frequently asked questions

Which specific bony notches are bridged by the sacrotuberous and sacrospinous ligaments?

The sacrotuberous and sacrospinous ligaments bridge the greater and lesser sciatic notches of the hip bone.

  • Greater sciatic notch (incisura ischiadica major) — converted by the sacrospinous ligament (lig. sacrospinale) and sacrotuberous ligament (lig. sacrotuberale) into the greater sciatic foramen.
  • Lesser sciatic notch (incisura ischiadica minor) — converted by the same ligaments into the lesser sciatic foramen.
Which muscles and neurovascular bundles pass through the greater sciatic foramen?

The greater sciatic foramen transmits the piriformis muscle (m. piriformis), which divides it into two compartments that transmit neurovascular bundles.

  • Suprapiriform foramen (foramen suprapiriforme) — transmits the superior gluteal neurovascular bundle (superior gluteal artery, veins, and nerve).
  • Infrapiriform foramen (foramen infrapiriforme) — transmits the inferior gluteal neurovascular bundle, the sciatic nerve (n. ischiadicus), the posterior femoral cutaneous nerve, and the pudendal neurovascular bundle.
What passes through the lesser sciatic foramen?

The lesser sciatic foramen transmits muscular and neurovascular structures heading toward the gluteal region and the ischioanal fossa.

  • Obturator internus muscle (m. obturatorius internus) — exits the pelvic cavity to reach the posterior aspect.
  • Pudendal neurovascular bundle — re-enters the pelvic cavity. It consists of the internal pudendal artery (a. pudenda interna), internal pudendal veins (vv. pudendae internae), and the pudendal nerve (n. pudendus).
What continuous connections (synarthroses) form the hip bone itself?

The hip bone itself is formed by continuous cartilaginous connections—temporary synchondroses.

  • Temporary synchondroses persist until puberty.
  • In the region of the acetabulum, they unite the three component parts of the hip bone: the pubis, ischium, and ilium.
Where is the obturator membrane located and what is its function?

The obturator membrane (membrana obturatoria) is located across the obturator foramen on the anterolateral wall of the pelvis.

It serves as a site of origin for the obturator internus muscle (m. obturatorius internus) from its inner surface.

What type of joint is the sacroiliac joint?

It is a plane joint that functions as an amphiarthrosis (a slightly movable joint).

What structures form the pubic symphysis?

The pubic symphysis is formed by the surfaces of the pubic bones, between which lies a fibrocartilaginous disc (sometimes containing a slit-like cavity), along with the superior pubic and arcuate pubic ligaments.

Which ligaments close the sciatic notches into foramina?

The greater and lesser sciatic foramina are formed by the sacrotuberous (lig. sacrotuberale) and sacrospinous (lig. sacrospinale) ligaments.

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