Os coxae (Hip bone):
• Each hip bone comprises three significant flat bones—ilium, ischium, and pubis.
• These bones unite to create a spacious acetabular cavity that connects with the femoral head.
ILIUM:
• A triangular flat bone positioned at the craniolateral aspect of the pelvis.
• It features two surfaces (gluteal and sacropelvic surfaces), three angles (medial, lateral, distal), and three borders (cranial or crest, medial, lateral).
• The upper section is flat, known as the wing, and the lower part is slender and considered as the shaft.
Gluteal surface:
• Broad and concave cranially.
- Narrow and convex distally.
• Gluteal surface is intersected by the curved gluteal line, extending from the midpoint of the medial border toward the tuber coxae.
• This surface is occupied by the Gluteus muscle.
Sacropelvic surface:
• The sacropelvic surface faces the pelvic cavity.
- Medially it has a triangular area for articulating with Sacrum.
- Laterally it has a quadrilateral area, which is covered by the iliacus muscle.
Angles of Ilium
1. External Angle (Lateral angle):
• The external angle is referred to as the tuber coxae.
• It is enlarged and exhibits 3 to 4 tuberculous prominences.
- It contributes towards formation of point of Hip.
- It is in the form of a large rough quadrangular mass for attachment of muscle.
2. Internal Angle (Medial angle):
• The internal angle is blunt and tilts backward.
• This angle is known as the tuber sacrale, as it articulates with the wings of the sacrum.
3. Distal or Cotyloid Angle:
• The distal (cotyloid) angle is expanded and combines with the corresponding angles of the pubis and ischium to form the cotyloid cavity.
• Towards the cranial aspect of this angle, there exists a fossa for the origin of the rectus femoris muscle, which can be termed as the supra-acetabular fossa.
• In the middle of the medial surface of the shaft, there is an elevated prominence known as the psoas tubercle, serving for the attachment of the psoas minor muscle.
Borders of ilium
1. Dorsal border / Cranial border / Crest of ilium – thin and concave.
2. Lateral border – thin, rough, and also concave.
3. Medial border
- It is concave and at the beginning of the shaft it divides into one anterior (pubic) and a posterior (ischiatic) border.
- The anterior becomes continuous with the anterior border of the pubis.
- The posterior one forms the greater ischiatic notch and is then raised on the cotyloid cavity to form the superior ischiatic spine.
ISCHIUM
- It is roughly a quadrilateral plate of bone.
- It is situated behind the pubis.
- It forms most of the pelvic floor.
- It has two surfaces, four borders, and four angles.
Surfaces
- The dorsal (pelvic) surface is concave and smooth and presents an impression of the obturator internus muscle close to the obturator foramen.
- Ventral surface is slightly convex and rough for the origin of the adductor muscle.
Borders
- The cranial border is concave and thin. It forms the caudal boundary of the obturator foramen.
- The caudal border is thick and inclined forward and forms ischial arch by joining with its fellow.
- The lateral border is concave and forms the lesser ischiatic notch.
- The medial border joins with the similar border of the bone of the opposite side and forms the ischial symphysis.
- Ventrally in the middle of the symphysis there is a prominence, known as the ventral tubercle.
Angles
- The cranio-internal angle is narrow and joins with the caudal angle of the pubis.
- The cranio-external angle is wide and joins with the cotyloid angles of ilium and pubis to form a cotyloid cavity.
- The caudo-internal angle meets with the similar angle of the other bone at the middle of the ischial arch.
- Caudo-external angle is expanded to form a trifid structure called ischial tuberosity or tuber ischii. This prominent tuber ischii is sometimes referred as pin bone.
PUBIS
- It is a small triangular shaped plate of bone.
- It is present at the cranio-medial side of the pelvic floor.
- It consists of two surfaces, three angles, and three borders.
Surfaces of Pubis
1. Dorsal Surface
- The dorsal (pelvic) surface is either smooth or occasionally slightly depressed.
- It accommodates the body of the urinary bladder.
2. Ventral surface
- The ventral surface is convex.
- It is rough in appearance for attachment of muscles.
Borders of Pubis
- The cranial border is slender (thin), slightly depressed, and exhibits a prominence on the lateral aspect known as the ilio-pubic eminence.
- The lateral border is thin and concave and forms the cranial boundary of the obturator foramen.
- The medial border contributes to the formation of the pubic symphysis, joining with the corresponding border of the opposite bone.
Angles of Pubis
- The cranio-lateral or acetabular angle is wide and connects with both the ischium and ilium.
- The cranio-medial angle unites with its corresponding angle on the opposite side at the pubic symphysis.
- The caudal angle is narrow and merges with the cranio-medial angle of the ischium.
Acetabulum
- The cotyloid cavity, or acetabulum, results from the convergence of corresponding angles of the ilium, ischium, and pubis, providing a socket for the femoral head.
- Placed Ventro-laterally in the pelvic girdle.
- Comprises two segments—an articular part and a non-articular part.
Articular part:
• The articular part is smooth in texture, located externally, and referred to as Facies lunata.
• The medial section of the rim of the articular part is interrupted by the acetabular notch.
Non-articular part:
• The non-articular part, known as the acetabular fossa, is situated in the center and is the deeper portion of this fossa.
• It serves as the point of attachment for the round ligament.
- It is also linked to the acetabular notch.
Obturator foramen
- It is the largest foramen of the body situated between the pubis and ischium.
- It is an oval or egg-shaped aperture whose axis is directed outward and forward.
- In lifetime it is closed by fibrous membranes and muscles, leaving a narrow space for passage of vessels and nerves.
- The muscles covering the foramen externally and internally are obturator externus and obturator internus respectively.
- Important terms related to Os coxae
Pelvic inlet
- It is the cranial opening of pelvic girdle.
- It is formed by the cranial border of sacrum, body of Ilium and the cranial border of pubis.
- The pelvic outlet
- It is caudal opening of pelvic girdle.
- It is formed by coccygeal vertebra above and ischial arch and ischial tuberosity below.
- Perinium
- Lateral walls of pelvic outlet are covered by caudal borders of Sacro sciatic ligaments.
- This is covering is known as Perinium.
4. Conjugate Diameter
- It is the distance between body of sacrum and cranial end of pubic symphysis.
5. Transverse diameter
- It is the distance between the two psoas tubercles.
Differences in the male and female Os coxae
1. The transverse and conjugate diameters are greater in females than in males.
2. In females, the bone is inclined more forward.
3. The pelvic outlet and ischial arch are larger and wider in females.
4. The ischia on both sides join at a wider angle in females, creating a more spacious cavity.
Os coxae of horse
1. It is more inclined forward.
2. Gluteal line is not prominent.
3. Ventral tubercle is absent.
4. The ischial tuberosity is not trifid.
5. The superior ischiatic spine is not sharp.
6. Cotyloid cavity is very wide.
7. Acetabular notch is also wide.
8. The secondary acetabular notch is absent.
9. Tuber sacrale is further inclined backward.
10. Psoas tubercle is underdeveloped.
11. Supra acetabular fossa is not prominent.
Os coxae of dog
1. The ilium of left side and that of right side are almost parallel to each other.
2. The gluteal surface of the ilium is concave.
3. The crest of ilium is strongly convex.
4. Ischium is twisted.
5. Ischial tuberosity is flat.
6. The superior ischiatic spine is blunt and both the greater and lesser ischiatic notches are shallow.
7. Acetabular notch is wide.
Os coxae of pig
1. The ilium is not much extended laterally.
2. The dorsal border of the ilium is convex.
3. The tuber sacrale is inclined caudally.
4. The ischial tuberosity bears three prominences.
5. The psoas and pectineal tubercles are prominent.
6. The rim of acetabulum is thicker.
Os coxae of fowl
1. The ilia are fused with the sacrum.
2. The pubis is long and in the form of a thin elongated stick.
3. The Acetabulum is perforated.
4. Between the ilium and ischium, there is an extra-large aperture, known as ilioischiatic foramen.
CLICK BELOW TO SEE THE 3D VIEW OF OS COXAE
