Hip Anatomy

The hip is one of the most important joints for supporting the body's weight during biomechanical movements and when standing. This is due to the anatomy of this joint area, in which a series of ligaments and muscles come together to act precisely with the bones.

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Parts and anatomy of the hip

Bones and joints

The bones that make up the hip are the ilium (the upper part of which is known as the iliac crest), the sciatic spine, the ischium, the sacrum, the pubis, the acetabulum and the coccyx. The sciatic spine, in women, is displaced in relation to the pelvic cavity, the latter being much more open in the case of women so as not to obstruct the birth canal.

Within the hip are also the sacroiliac and coxofemoral joints. The first joint connects the iliac crest to the lumbar spine, forming the characteristic movements of the lower back. The second joint connects the head of the femur to the socket of the acetabulum, enabling the person to walk and perform other movements according to the amplitude of this joint body.

Muscles

• Piriformis: The purpose of this muscle is to allow external rotation, extension and adduction at the hip. It originates from the sacrum and inserts into the greater trochanter at the upper edge.
• Psoas iliacus: Located in the anterior area of the thigh, inside the abdominal cavity. The work of this muscle is to move the trunk and produce hip flexion. The internal iliac fossa and the lumbar vertebrae are its origin, while the trochanter of the femur is its insertion site.
• Tensor of the fascia lata: It is a thin, flattened muscle found on the gluteus. Its function is to stabilise hip movements and knee extension. It arises from the iliac spine and inserts into the lateral tendons of the fascia lata called the iliotibial band.
• Adductor: This muscle consists of three parts named adductor minimus, medius and adductor magnus. It originates from the pubis and ischium and inserts into the femur. Its job is to flex, rotate and stabilise the spine and pelvis.
• The gracilis: It is also known as the internal rectus and has several insertions, which are the symphysis pubis, the medial condyle of the tibia and some internal tendons. Internal rotation, abduction and flexion of the hip are the functions of this muscle.
• Pectineus: The activity of this muscle is to move the leg together with the adductors. It inserts on the femur in the area of the pectineus line and originates from the iliopubic ramus.
• Rectus femoris: It arises from the iliac spine and inserts on the quadriceps tendon. Knee extension and hip flexion are the two actions performed by this muscle.
• Gluteus: Like the adductor, it can be divided into three sections, named gluteus maximus, gluteus medius and gluteus minimus. They are located in the anterior part of the hip and insert on the edge of the iliotibial tract muscles and on the gluteal tuberosity. They vary in strength being the sides and edges of the sacrum and coccyx, as well as the sacrotuberous ligaments.
• Geminus superior and geminus inferior: They are also known as the superior gemellus and inferior gemellus. They are found in the gluteal and femoral regions of the body whose job is to adduct the hip and cause movements in the coxofemoral joint body.
• Quadratus femoris: Also known as the quadratus cruris, it travels from the ischium to the intertrochanteric crest. Its action is to rotate the femur laterally.
• Obturator internus: Named after its origin in the obturator foramen of the hip, it inserts into the trochanter of the femur and into the femoral fossa. Its action allows external rotation of the hip.
• Obturator externus: The external margin of the obturator foramen is the origin of this muscle, and its insertion is into the tendon of the femoral neck. Abduction of the hip is caused by this muscle.
• Sartorius: It is the longest muscle in the human anatomy and its course is on the superficial part of the thigh. Its job is to flex the hip and move the femur away from the femur via the adductors, which creates the ability to walk or place a heel on a line above the opposite knee.

Ligaments

• Round or femoral head ligament: It runs from the acetabulum to the fossa in the femoral head. This allows the coxofemoral joint to function.
• Iliofemoral: This ligament divides in its lower part in two, causing an inverted "Y" shape. It arises from the iliac spine and inserts into the anterior area of the femur, within the trochanter line (in two different areas, hence the name for each subdivision, Superior and Inferior).
• Pubofemoral: Its origin is at the top of the pubis and inserts into the lower section of the ischiofemoral, taking into account the intertrochanteric line.
• Ischiofemoral: its origin is the ischium, running along the posterior part of the acetabulum bone until it ends a little below the head of the femur.
• Sacrotuberous: It is considered as a continuation of the biceps femoris, its origin is in the upper area of the coccyx, in the tubercles of the sacrum and in the lower area of the sacrum. It joins the iliac spine with other ligaments.
• Sacrospinous: This ligament runs from the ischial spine to the edges of the coccyx and sacrum. Its function is to produce hip movements and to strengthen other ligaments.

Biomechanics of the hip joint

• Extension: When the leg is placed behind the hip line, the gluteus and hamstrings open 20 to 30°, depending on the flexion of the knee. This movement is limited by the iliofemoral ligament.
• Flexion: With this action it is possible to touch the trunk with the front of the thigh. Its amplitude can be from 90 to 120°, taking into account the flexion that occurs in the knee. In this case the muscles that work are the sartorius, rectus abdominis, tensor fascia latae and psoas iliacus.
• Adduction: This consists of moving the leg to the side, without bending the knee and until it reaches hip height (in the case of lying on one leg), parallel to the axis of the body, causing symmetry with the body. The amplitude of this movement does not exceed 30° and the muscles involved are the pectineus, adductors and rectus internus.
• Abduction: Moving the foot forward, without bending the knee, causes the fascia lata, gluteus and piriformis muscles to work. This movement can have an opening that can reach 180° when the person trains so that the pubofemoral and iliofemoral ligaments do not limit the amplitude.
• Internal rotation: Every time there is an inward movement of the foot, this type of biomechanical action occurs in the hip. The muscles involved are the gluteus medius, gluteus minimus and tensor fascia latae. If the leg is considered as the axis, this movement causes a maximum opening of 40°.
• External rotation: This is the opposite movement to the previous point performed by the foot. In this case the amplitude can reach up to 60° due to the extension of the iliofemoral and pubofemoral ligaments. The quadratus cruris, sartorius, geminus superior and inferior, sartorius, obturator externus and obturator internus muscles are involved.
• Circumduction: These are the circular movements that the hip can perform, taking into account the combination of rotations, adduction, abduction, flexion and extension.