Overview
The hip bone (os coxae) results from the fusion of three bones, the ilium, ischium and pubis, which meet at the acetabulum. The two hip bones meet ventrally at the pelvic symphysis and articulate dorsally with the sacrum at the sacroiliac joints. In the cat the pelvis is long and narrow, with its axis almost parallel to the spine.
Key features
- Ilium: the cranial part. Its wing is narrow and elongated, with the palpable iliac crest and the auricular surface that articulates with the sacrum. The gluteal muscles arise from its lateral surface.
- Ischium: the caudal part, with the ischiatic tuberosity, palpable on each side of the tail base, origin of the hamstring muscles (biceps femoris, semitendinosus, semimembranosus). The ischiatic arch lies between the two ischia.
- Pubis: the ventral and medial part; it forms the cranial edge of the obturator foramen and the cranial part of the symphysis.
- Acetabulum: deep socket that receives the femoral head. Its articular surface is crescent-shaped (facies lunata), open ventrally at the acetabular notch, and surrounds the acetabular fossa, where the ligament of the femoral head attaches.
- Obturator foramen: large opening between the pubis and ischium, closed in life by a membrane and the obturator muscles.
Clinical relevance
- Pelvic fractures: among the most common fractures of the cat, nearly always from road accidents. They are usually multiple (the pelvic ring breaks in at least two places) and often come with sacroiliac luxation. Displaced fractures of the acetabulum or ilium usually need surgery.
- Narrowing of the pelvic canal: malunion of fractures reduces the canal diameter and can cause chronic constipation and megacolon.
- Hip dysplasia: in the cat it shows mainly as a shallow acetabulum with remodelling of its craniodorsal rim; the Maine Coon is predisposed. Clinical signs are usually mild.
- Associated injuries: in pelvic trauma the urethra, bladder and the sciatic and obturator nerves must be assessed.