ischi-, ischio- +

(Greek: hip, hip-joint, hip-bone; haunch)

ischialgia (s) (noun) (no pl)
Pain in the hip; specifically the ischium; ischiodynia: Olive suffered in the area of her hip, and Dr. Body told her that she had a case of ischialgia, having its source in a condition of osteonecrosis.

Patty read about ischialgia being a rarely used term for sciatica, a neuralgia of the sciatic nerve.

Ischialgia is also known ischioneuralgia.

Surgical removal or excision of the ischium (the inferior dorsal portion of the os coxae (hip bone); it is a separate bone in early life).
Symmetrical conjoined twins united at the pelvis.
ischiodynia (s) (noun) (no pl)
Agony in the hip: Ischiodynia specifically refers to the ischium (seat bone of the pelvis).
1. Pain in the hip; specifically, the ischium or the lower part of the hip.
2. A rarely used term for sciatica.

Sciatica refers to a syndrome characterized by pain radiating from the back into the buttock and into the lower extremity along its posterior or lateral aspect and most commonly caused by prolapse of the intervertebral disk. The term is also used to refer to pain anywhere along the course of the sciatic (referring to the hip) nerve.

Inflammation of the ischium or lower hip.
Conjoined twins fused at the ischia, the axes of the two bodies extending in a straight line but in opposite directions; according to the number of lower limbs shared, classified as bipus, tripus, and tetrapus.
ischium (s), ischia (pl)
The lower section, or part, of the hip bone.

Ischium is the bone which forms the lower and back part of the pelvis. It bears the weight of the body when sitting.

os ischia
Hip joint.