📝 STANDARD DESCRIPTION:
Large irregular bone of pelvic girdle.
Ox Standard — formed by fusion of 3 bones at ACETABULUM:
- Ilium (cranial, largest)
- Ischium (caudal)
- Pubis (medial, ventral)
Important Palpable Landmarks:
- Tuber Coxae = HOOK BONE (cranial angle of ilium)
- Tuber Sacrale = top angle, near sacrum
- Tuber Ischiadicum = PIN BONE (caudal angle of ischium)
Other Features:
- Acetabulum: cup-shaped socket for head of femur (with acetabular notch & fossa).
- Obturator Foramen: large oval hole between pubis & ischium; transmits OBTURATOR NERVE.
- Pelvic Symphysis: midline fusion of right & left pubis + ischium.
📚 DETAILED DESCRIPTION:
THE HIP BONE — OS COXAE
Each os coxae is a large flat-irregular bone made of 3 bones fused at the acetabulum:
• Ilium — wing-shaped, points cranially toward the sacrum.
• Ischium — caudal, forms the floor and back wall.
• Pubis — short, medial part forming the cranial floor.
The right & left os coxae meet ventrally at the pelvic symphysis and dorsally articulate with the sacrum at the sacroiliac joint — together they form the bony PELVIS (pelvic cavity = bony tunnel).
SURFACE LANDMARKS YOU CAN PALPATE on a live cow:
• Tuber Coxae (Hook bone): Cranio-lateral angle of the ilium; visible bump on the side of the rump. Used for body condition scoring.
• Tuber Sacrale: Dorso-medial angle close to the sacrum; the highest point of the rump.
• Tuber Ischiadicum (Pin bone): Caudal corner; sticks out on either side of the tail base.
The line joining hook → pin bones helps assess pelvic shape for calving ease.
ACETABULUM: A deep cup formed by all 3 bones (ilium, ischium, pubis meet here). The smooth crescent lunate surface articulates with the head of the femur; the acetabular fossa is non-articular and gives attachment to the round ligament.
OBTURATOR FORAMEN: The biggest hole in the body skeleton. Located between pubis & ischium. The obturator nerve and vessels exit here.
SEX DIFFERENCES: In the cow, the pelvic inlet is wider & more rounded (for calving); in the bull it is narrower & more V-shaped.
// COMPARATIVE ANALYSIS
| HORSE |
Pelvis narrower; acetabulum deeper. Tuber coxae very prominent (point of hip). |
| DOG |
Smaller, more horizontal pelvis. Common site of HIP DYSPLASIA — shallow acetabulum + loose hip → arthritis. |
| PIG |
Wide flat ilium; tuber coxae less obvious. |
| FOWL |
Os coxae fused with synsacrum (sacrum + lumbar + caudal vertebrae). Pubic symphysis OPEN in females (allows large egg passage). Renal fossa lodges kidneys. |
CLINICAL RELEVANCE
Pelvimetry: Measuring pelvic inlet in heifers before first calving — narrow inlet predicts dystocia.
Calving paralysis (downer cow): Compression of the obturator nerve as it crosses the floor of pelvis during difficult calf delivery → cow cannot rise; legs splay sideways.
Hip Dysplasia (Dog): Shallow acetabulum → loose hip joint → painful arthritis in large breeds.
