The human hip is a weight-bearing joint that needs to carry the weight of half of the body, in addition to any extra force that is acting up on it. It is a synovial joint, and comprises of a ball and socket. The hip needs to be both strong and
stable whilst providing a range of motions, including quick acceleration.
The bones of the hip joint are the pelvis and the femur. The pelvis is made up of three bones: the pubis, the ischium and the ilium, which together form the socket (acetabulum) part of the joint. At the top of the femur is the femoral head. This is round in shape, fitting into the socket in the pelvis.
Articular cartilage lines the outside of the femoral head and the inside of the acetabulum. As it is rubbery and smooth, it allows the two bones of the joint to move easily against each other and it absorbs shocks.
The bones are connected together by soft tissue called ligaments. Around the outside of the femur and pelvis are three ligaments, the iliofemoral, pubofemoral
and ischiofemoral ligaments, which join the femur head to the acetabulum. This join is known as a joint capsule, a watertight structure that stabilises the hip joint. Inside this capsule, there is a ligament (ligamentum teres) on top of the femoral head that attaches it to the inside of the acetabulum.
On top of the articular cartilage along the outside of the acetabulum is another, smaller ligament called the labrum. If the labrum becomes damaged, it can cause pain and a clicking hip joint.
There are 17 muscles that surround the hip. These muscles are subdivided
further into four groups according to their position around the hip joint. They are:
- The gluteal group (4 muscles):
The tensor fasciae latae, the gluteus minimus, the gluteus medius and the gluteus maximus
- The adductor group (5 muscles):
The adductor brevis, the adductor magnus, the adductor longus, the gracilis and the pectineus
- The lateral rotator group (6 muscles):
The externus and internus obturators, the piriformis, the superior and inferior gemelli, and the quadratus femoris
- The iliopsoas group (2 muscles):
The iliacus and the psoas major
The muscles in the gluteal group allow for extension, pulling the thigh backwards, and abduction, pulling the thigh away from the other. They also help to keep the pelvis level as the weight is shifted from one leg to the other during walking.
The adductor muscles main function is adduction, which is pulling the leg inwards to the opposite thigh.
The lateral rotator group all work together to create external (lateral)
rotation (when the thigh and knee rotate outward, away from the body),
internal (medial) rotation (when the thigh and knee rotate inward, towards the body) and circumduction (where the limb can be moved in a circular motion). This group also helps to keep the hip stable.
Finally, the iliopsoas group help to form the forward motion required for walking, and both muscles are involved in flexion - when the leg or knee is raised forwards towards the torso.
Hip related AnatomyStuff resources