Which joint surface is the proximal surface of the hip joint?

The acetabulum is the correct choice for the proximal surface of the hip joint. This structure is a deep, cup-shaped socket located on the lateral aspect of the pelvis. It serves as the articulation point for the head of the femur, thereby forming the hip joint. This joint is a ball-and-socket type, which allows for a wide range of motion in various directions.

The acetabulum is crucial for stability and mobility in the hip joint. It is positioned to accommodate the spherical head of the femur, creating a secure connection that bears weight and facilitates movements such as walking, running, and jumping. The surface of the acetabulum is lined with cartilage, which helps reduce friction and absorb shock during activities.

In contrast, the greater trochanter refers to a bony prominence on the femur where muscles attach; it is not a joint surface. The anatomical neck of the femur is situated just below the head of the femur, and while it plays a role in stability, it is not the articulating surface itself. The ischium is a part of the pelvic bone and contributes to the structure of the acetabulum but is not involved directly in forming the joint surface of the hip. Therefore, the acet