Leg bondage
From Voyeurweb's Wiki about Sex
Leg bondage may be part of a bondage position and sexual bondage games. It typically means to immobilize her knees by using a rope, which goes around her thigh and her lower leg or ankle on both of her legs. She usually lies on her back during leg bondage. Once her knees are unable to unfold, she will feel somehow uncomfy and she is not able to stretch her legs. The lack of being able to move her legs freely might add to her sexual excitement, especially when stimulated.

