PUBIS

 

The pubis is one of the three main bones that forms the pelvis. It is also known as the pubic bone or pelvic girdle. It constitutes the lower and anterior part of each side of the hip. Pubis bone is the most forward-facing and the smallest bone of the three bones that make up the hip bone. It is located at the front of the body, just below the abdomen.

The primary function of the pubis is to protect the urinary and reproductive organs. Its structure and function differ between individuals assigned female at birth and those assigned male at birth.

The pubis bone has two halves: right and left. It is connected by a cartilage called pubic symphysis. In most adults, the pubic symphysis is not completely rigid and can move by around 2 millimeters. It is covered by a layer of fat – the mons pubis.

The pubis bone is divided into three sections: 

A. Body 

B. Superior Pubic Ramus 

C. Inferior Pubic Ramus.

A.   BODY

The body is the largest portion of the pubis, forming the wide, strong, middle and flat part of the pubic bone. The body has a superior border or pubic crest, pubic tubercle at the lateral end of the pubic crest and three surfaces: anterior, posterior & medial.

The rough upper edge is the pubic crest, ends laterally at the pubic tubercle. The pubic crest separates the anterior and posterior surface of the bone. The tubercle is roughly 3cm from the pubic symphysis. The tubercle has a distinctive feature on the lower part of the abdominal wall and is important when localizing the superficial inguinal ring & femoral canal of inguinal canal. Both pubic crest and pubic tubercle are palpable and are partly obscured in males by the spermatic cord that crosses above it from the scrotum to the anterior abdominal wall

Surfaces

A. Anterior or External Surface: The smooth anterior surface faces the inferolateral side. The smooth posterior surfaces face upwards and backwards as the oblique anterior wall of the lesser pelvis and is related to the urinary bladder. The rough surface faces superomedially.

B. Posterior or Internal Surface: It faces posterosuperiorly, forming the anterior wall of the lesser pelvis. It is separated from the urinary bladder by the retropubic fat.

C. Medial or Symphyseal Surface: The medial surface which is elongated and oval, of the pubic bone of left and right hip bones articulate with each other via symphyseal cartilage forming the pubic symphysis joint. Removing the cartilage it has an irregular surface of small ridges and furrows or nodular elevation carrying considerably with age, features that are of forensic interest. The curved area below the pubic symphysis is known as the pubic arch, one of the sexually dimorphic areas of the pelvis. The males, this arch is a V-shaped whereas in females it is usually broader.

 

B.   SUPERIOR PUBIC RAMUS

The superior pubic ramus is 1/3^rd of the pubic bone. It starts at the pubic tubercle and extends postero-laterally and upwards to the acetabulum, joining the ilium and ischium. It forms the upper edge of the obturator foramen. It appears triangular in cross section and has three surfaces and three borders:

SURFACES

Anterior (Pectineal) surface: It is tilted slightly up, is triangular in outline and extends from the pubic tubercle to the iliopubic ramus. It is bounded in front by the rounded obturator crest and behind by the sharp pecten pubis also known as pectin line which with the crest, is the pubic part of the linea termanilis that is anterior part of the pelvic brim. Pelvic brim separates the greater and lesser pelvis.

Obturator Surface: It faces posteroinferiorly and is bounded anteriorly by the obturator crest and inferiorly by its sharp inferior border. It also gives attachment to the obturator membrane.

Inferior Surface: It part of the anterior boundary of the lesser pelvis. The surface is medially inclined, smooth, convex from downward. It is limited by the pecten pubis above and the sharp inferior border below.

BORDERS

Superior Border: It is also known as the pectin line or pecten pubis. The superior border has a sharp crest which extends from just behind the pubic tubercle to the posterior part of iliopubic eminence. It projects forward, the inferior crus of the subcutaneous inguinal ring and inguinal ligament are attached to it. The pectin line marks the brim of the lesser pelvis.

Anterior Border: It is also known as the obturator crest. The border is a rounded ridge, extending from the pubic tubercle to the acetabular notch. The junction of the pubic crest and to the medial part of the pubic bone is known as the angle. The border is articular and is marked by 8 to 9 transverse ridges which serve for the attachment of a thin layer of cartilage which intervenes between it and the interpubic fibrocartilaginous lamina.

Inferior Border: It is a sharp and forms the upper margin of the obturator foramen.

C.   INFERIOR PUBIC RAMUS

The inferior ramus is thin and flat, which passes laterally and downward from the medial end of the superior ramus and makes up 1/3^rd part of the pelvis. It becomes narrower as it descends and joins with the inferior ramus of the ischium below the obturator foramen. The joint may be locally thickened but not so obviously in adults. It has two surfaces and two borders.

SURFACES

Anterolateral Surface: The surface is rough and is directed towards the thigh, running superiorly to the body of the pubis. The surface is limited laterally by the margin of the obturator foramen.

Posteromedial Surface: It is continuous above with that of the body and is transversely convex. The medial part is often everted in males and gives attachment to the crus of the penis in males and clitoris in females. This surface faces the perineum medially; its smooth lateral part tilted up towards the pelvic cavity.

BORDERS

Medial Border: The border in the females is thick, rough and everted. It has two ridges separated by an intervening space. The ridge extends downwards and are continuous with the similar ridges on the inferior ramus of the ischium.

Lateral Border: It is thin and sharp; forms part of the circumference of the obturator foramen.

 

MUSCLE ATTACHMENTS

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 pubic 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 pubic 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 pubic crest.

3.    Ventral pubic ligament: At the medial aspect of the anterior surface of the body.

4.    Puboprostatic ligament: At the pelvic surface of the body.

5.    Lacunar and pectineal ligament: At the pecten pubis.

Ossification

Ossification of the pubis occurs at two ossification centers; these are found in the:

- superior pubic ramus, which appears in utero during the fourth to fifth months.

- body of pubis, which appears during early to middle adolescence.

These ossification centers fuse with each other during middle adolescence to early adulthood. Fusion between the body of ilium, body of ischium, and superior pubic ramus occurs at the acetabulum during middle to late adolescence, forming the fused hip bone. Fusion between the ramus of ischium and inferior pubic ramus occurs within the seventh to eighth years, forming the fused ischiopubic ramus.

Compiled & Written by Dr. Palak Shah