Which structure does not contribute to the boundaries of the pelvic outlet?

The ischial spine does not contribute to the boundaries of the pelvic outlet.

The pelvis is the lower part of the trunk of the human body  present between the thighs and abdomen or the embedded skeleton in it. The pelvis has the main function of providing support for the intestine and contains reproductive organs and the bladder.

The space enclosed by the lower circumference of the lesser pelvis is called the pelvic outlet and is irregular structure. The boundaries of pelvic outlet are: pubic arch, the tip of coccyx, inferior margin of sacrotuberous ligament and the ischial tuberosities.

Ischial spine is an eminence or outgrowth triangular in shape and provides attachment to different internal and external structures.