Pubis (Pubic Bone)

What is the Pelvis

The pelvis is one of the three bones that unite to form the hip bone, the other two being the ilium and ischium. It is the frontal section of the hip bone.

Where is the Pelvic Bone Located

The pelvic bone is situated at the frontal part of the hip bone, near the reproductive organs.

Key Facts

Functions

Given its part in the pelvis, it safeguards numerous essential organs within the abdominal cavity, such as the urinary bladder and reproductive organs.

Components and Structure

The pelvic bone or pubis is the smallest part of the hip bone. It consists of a small body situated anteromedially and two rami, superior pelvic ramus and inferior pelvic ramus, extending posterolatery from the body. The rami of the pelvic bone resemble the letter ‘K’ from an anterior view. Together, these two rami enclose part of the obturator foramen through which the obturator nerve, artery, and vein pass to reach the lower limb.

1. Body

The main part of the pelvic bone has three surfaces — front (external), back (internal), and symphyseal (medial) — that merge, except at the pelvic crest located at the anterosuperior part of the body. It marks the transition from external to internal surfaces. This crest ends laterally as the pelvic tubercle, where the medial end of the inguinal ligament attaches.

External (Front) Surface: The smooth front surface faces the inferolateral side. The adductors of the thigh attach here.

Internal (Back) Surface: This surface faces posterosuperiorly, forming the front wall of the lesser pelvis.

Symphyseal (Medial) Surface: The medial surface of the pelvic bone of left and right hip bones articulate with each other via symphyseal cartilage, forming the pelvic symphysis joint. The curved area below the pelvic symphysis is known as the pelvic arch, one of the sexually dimorphic areas of the pelvis. In males, the arch is v-shaped, whereas, in females, it is usually broader.

Pelvic Crest: The upper aspect of the body is marked by a rounded thickening called the pelvic crest. This crest separates the front and back surfaces of the bone. On its lateral end, the pelvic crest features the pelvic tubercle. This tubercle serves as a point of attachment for the inguinal ligament.

2. Superior Pelvic Ramus

The superior pelvic ramus is one-third of the pelvic bone. It starts at the pelvic tubercle and extends posterolaterally and upwards to the acetabulum, joining the ilium and ischium. It appears triangular in cross-section, having three surfaces.

Pectineal (Front) Surface: Extending from the pelvic tubercle to the iliopubic ramus, this surface is delimited anteriorly by the round obturator crest and by the pectineal line or pecten pubis posteriorly. The pectineal line is continuous with the arcuate line of the ilium. The pectineal and arcuate lines collectively form the linea terminalis or pelvic brim that separates the greater and lesser pelvis.

Obturator Surface: This surface faces posteroinferiorly and is bounded anteriorly by the obturator crest and inferiorly by its sharp inferior border.

Pelvic surface: The pelvic surface is relatively smooth and faces posterosuperiorly. It is limited by the pecten pubis above and the inferior border below.

3. Inferior Pelvic Ramus

The inferior pelvic ramus is thin and flat, making up one-third of the pelvis. It passes laterally and downward from the medial end of the superior ramus and becomes narrower as it descends to unite with the ischial ramus to complete the obturator foramen. It has two surfaces, anterolateral and posteromedial, which remain separated by the front and medial margins.

Anterolateral Surface: It is directed towards the thigh, running superiorly to the body of the pelvis.

Posteromedial Surface: This surface faces the lesser pelvis, where the crus of the penis (males) or clitoris (females) attach.

Articulations

• The pelvic bones of the left and right hip articulate through a cartilaginous joint called the pelvic symphysis.
• The bone also fuses with the other two components of the hip bone, ilium, and ischium.

Muscle and Ligament Attachments

Several vital muscles and ligaments insert or originate from the pelvic bone.

Muscles

Originating from the pubis

1. Gracilis and adductor brevis muscle: From the external surface of the body and inferior ramus
2. Obturator externus muscle and obturator internus muscle: From the external surface of the body
3. Adductor longus: From the upper body of the pubis just below the pelvic crest
4. Pectineus muscle: From the external surface of the superior ramus
5. Sphincter urethrae: From the conjoint ramus

Inserting into the pubis

1. Rectus abdominis muscle: On the lateral side of the pelvic crest
2. Pyramidalis muscle: Just below the attachment of the rectus abdominis muscle
3. Levator ani muscle (levator prostatae and puborectalis): on the medial surface of the body

Ligament Attachments

1. Pubofemoral and obturator ligament: At the obturator crest.
2. Inguinal ligament (Poupart ligament): At the pelvic crest.
3. Ventral pelvic ligament: At the medial aspect of the frontal surface of the body.
4. Puboprostatic ligament: At the pelvic surface of the body.
5. Lacunar and pectineal ligament: At the pecten pubis.

References

1. Pelvis – Radiopaedia.org
2. The Hip Bone – Teachmeanatomy.info
3. Hip bone – Kenhub.com
4. Bony pelvis – Kenhub.com
5. Pelvic Bone – Sciencedirect.com