Final answer:
The hip joint functions to provide stability, allow movement, and support weight-bearing and balance during a unilateral stance due to its ball-and-socket structure and supporting ligaments.
Step-by-step explanation:
The function of the hip joint during unilateral stance includes providing stability and support, allowing for movement and flexibility, as well as assisting in weight-bearing and balance. As a multiaxial ball-and-socket joint, the hip joint connects the head of the femur with the acetabulum of the hip bone. It supports the weight of the body, with a range of motion that is more limited than at the shoulder to ensure stability during weight-bearing activities. The supporting ligaments such as the iliofemoral, pubofemoral, and ischiofemoral contribute to this stability, especially when standing.