📝 STANDARD DESCRIPTION:
Type: Synovial BALL-and-SOCKET (multiaxial).
Articulation: Head of femur in acetabulum.
Movements: Flexion, extension, slight abduction, adduction, rotation.
Ligaments:
1. Joint capsule — encloses the joint.
2. Round Ligament (Lig. capitis femoris) — from fovea capitis of femur to acetabular fossa. Holds head in socket.
3. Accessory Ligament (HORSE only!) — extra ligament from prepubic tendon to fovea capitis. Prevents abduction → that's why horses can't kick sideways like dogs.
Acetabular Labrum: fibrocartilage rim that deepens the socket.
📚 DETAILED DESCRIPTION:
HIP / COXOFEMORAL JOINT
The hip is a true ball-and-socket joint — it allows movement in all directions but its main movement is flexion/extension in the sagittal plane.
BONES: Head of femur (ball) + acetabulum of os coxae (socket).
JOINT-DEEPENING: The acetabular labrum is a ring of fibrocartilage that increases the depth of the socket and improves stability.
LIGAMENTS:
• Joint capsule: Strong fibrous sleeve enclosing the joint.
• Ligament of head of femur (Round ligament): Inside the joint — runs from the fovea capitis on the femoral head to the acetabular fossa. It carries a small artery to the femoral head in young animals.
• Accessory Ligament — UNIQUE TO HORSE: An extra strong band running from the prepubic tendon, through the acetabular notch, to the fovea capitis. It limits ABDUCTION (sideways movement) of the limb. This is why a horse cannot abduct its hindlimb much (cannot 'kick sideways' like a dog can). In other species this ligament is absent.
MOVEMENTS:
• Flexion-extension (main range of motion).
• Some abduction-adduction (limited in horse by accessory ligament).
• Some rotation.
CLINICAL — HIP DYSPLASIA (DOG):
Inherited condition in large dogs (German Shepherd, Labrador, Saint Bernard) where the acetabulum is shallow + femoral head is loose → joint instability → secondary arthritis. Diagnosed by X-ray hip score; managed by weight control, anti-inflammatories, or surgery (Triple Pelvic Osteotomy or Total Hip Replacement).
// COMPARATIVE ANALYSIS
| HORSE |
Has the unique ACCESSORY ligament → limited abduction. |
| DOG |
No accessory ligament → wide range of abduction (allows the dog to lift its leg). Hip dysplasia common. |
CLINICAL RELEVANCE
Hip Dysplasia (Dog): Most common orthopaedic problem in large breeds.
Coxofemoral Luxation (Dog): Dorso-cranial dislocation of femoral head after road accident — limb shortened, toe touches ground, leg held adducted.
