The hip joint is the largest weight-bearing joint in the human body. It is also referred to as a ball and socket joint and is surrounded by muscles, ligaments, and tendons. The thigh bone or femur and the pelvis join to form the hip joint.
Any injury or disease of the hip will adversely affect the joint's range of motion and ability to bear weight.
The hip joint is made up of the following:
- Bones and joints
- Ligaments of the joint capsule
- Muscles and tendons
- Nerves and blood vessels that supply the bones and muscles of the hip
Bones and Joints
The hip joint is the junction where the hip joins the leg to the trunk of the body. It is comprised of two bones: the thigh bone or femur and the pelvis which is made up of three bones called ilium, ischium, and pubis. The ball of the hip joint is made by the femoral head while the socket is formed by the acetabulum. The Acetabulum is a deep, circular socket formed on the outer edge of the pelvis by the union of three bones: ilium, ischium, and pubis. The lower part of the ilium is attached by the pubis while the ischium is considerably behind the pubis. The stability of the hip is provided by the joint capsule or acetabulum and the muscles and ligaments which surround and support the hip joint.
The head of the femur rotates and glides within the acetabulum. A fibrocartilagenous lining called the labrum is attached to the acetabulum and further increases the depth of the socket.
The femur or thigh bone is one of the longest bones in the human body. The upper part of the thigh bone consists of the femoral head, femoral neck, and greater and lesser trochanters. The head of the femur joins the pelvis (acetabulum) to form the hip joint. Next, to the femoral neck, there are two protrusions known as greater and lesser trochanters which serve as sites of muscle attachment.
Articular cartilage is the thin, tough, flexible, and slippery surface lubricated by synovial fluid that covers the weight-bearing bones of the body. It enables smooth movements of the bones and reduces friction.
Ligaments are fibrous structures that connect bones to other bones. The hip joint is encircled with ligaments to provide stability to the hip by forming a dense and fibrous structure around the joint capsule. The ligaments adjoining the hip joint include:
Iliofemoral ligament: This is a Y-shaped ligament that connects the pelvis to the femoral head at the front of the joint. It helps in limiting the over-extension of the hip.
Pubofemoral ligament: This is a triangular shaped ligament that extends between the upper portion of the pubis and the iliofemoral ligament. It attaches the pubis to the femoral head.
Ischiofemoral ligament: This is a group of strong fibers that arise from the ischium behind the acetabulum and merge with the fibers of the joint capsule.
Ligamentum teres: This is a small ligament that extends from the tip of the femoral head to the acetabulum. Although it has no role in hip movement, it does have a small artery within that supplies blood to a part of the femoral head.
Acetabular labrum: The labrum is a fibrous cartilage ring which lines the acetabular socket. It deepens the cavity, increasing the stability and strength of the hip joint.
Muscles and Tendons
A long tendon called the iliotibial band runs along the femur from the hip to the knee and serves as an attachment site for several hip muscles including the following:
Gluteals: These are the muscles that form the buttocks. There are three muscles (gluteus minimus, gluteus maximus, and gluteus medius) that attach to the back of the pelvis and insert into the greater trochanter of the femur.
Adductors: These muscles are located in the thigh which helps in adduction, the action of pulling the leg back towards the midline.
Iliopsoas: This muscle is located in front of the hip joint and provides flexion. It is a deep muscle that originates from the lower back and pelvis and extends up to the inside surface of the upper part of the femur.
Rectus femoris: This is the largest band of muscles located in front of the thigh. They also are hip flexors.
Hamstring muscles: These begin at the bottom of the pelvis and run down the back of the thigh. Because they cross the back of the hip joint, they help in extension of the hip by pulling it backward.
Nerves and Arteries
Nerves of the hip transfer signals from the brain to the muscles to aid in hip movement. They also carry the sensory signals such as touch, pain, and temperature back to the brain.
The main nerves in the hip region include the femoral nerve in the front of the femur and the sciatic nerve at the back. The hip is also supplied by a smaller nerve known as the obturator nerve.
In addition to these nerves, there are blood vessels that supply blood to the lower limbs. The femoral artery, one of the largest arteries in the body, arises deep in the pelvis and can be felt in front of the upper thigh.
All of the anatomical parts of the hip work together to enable various hip movements. Hip movements include flexion, extension, abduction, adduction, circumduction, and hip rotation.
The gluteal muscles (situated in the buttocks) are necessary for the stability and movement of the hip joints. The tendons of two gluteal muscles (gluteus medius and gluteal minimus) are attached at the outer hip region and are often called the “rotator cuff of the hip.”
Stress fractures of the hip are a break in the upper part of the thigh bone (femur) that fits into the socket of the hip joint. It can occur in any part of the hip, however, it mostly occurs just below the ball of the ball-and-socket hip joint called the femoral neck.
A hip labral tear is an injury to the labrum, the cartilage that surrounds the outside rim of your hip joint socket. The labrum helps to deepen the socket and provide stability to the joint. It also acts as a cushion and enables smooth movement of the joint.
Hip synovitis, also called transient hip synovitis or toxic synovitis, is a condition characterized by inflammation of the synovial tissues that surround the hip joint. It is the most common cause for sudden hip pain that occurs in young children between the age of 2 and 9. It affects boys more commonly than girls and is most of the time limited to only one side of the hip.
Developmental dysplasia of the hip (DDH) or hip dysplasia is a condition that is seen in infants and young children because of developmental problems in the hip joint. The femur (thighbone) partially or completely slips out of the hip socket leading to dislocation at the hip joint. It is most common in the first-born baby with a family history of the disorder.
Irritable hip, also known as acute transient synovitis, is a common disorder of childhood characterized by hip pain and limping. The term transient means that it does not last long. It usually occurs before puberty and affects only one hip. Boys aged between 4 to 10 years are most often affected.
The hip joint consists of the femur (thighbone) and pelvic bone, which is made up of the fusion of three bones – the ischium, pubis, and ilium. The femur has two boney prominences close to the hip joint – the greater and lesser trochanters. Hip pointer is an injury or bruise to the iliac crest (curved upper border of the ilium) or greater trochanter, or the surrounding muscles or tissues.
The inflammation of the joints is referred to as arthritis. Inflammation arises when the smooth lining called cartilage at the ends of bones wears away. In some cases, the inflammation is caused when the lining of the joint becomes inflamed as part of an underlying systemic disease.
The hamstring is a group of three muscles that run along the back of the thigh from the hip to the knee. Hamstring injuries occur when these muscles are strained or pulled. They are common in dancers and athletes of all sorts including runners and those who play football, soccer, basketball, tennis, etc.
Physical therapy is an exercise program that helps you to improve movement, relieve pain, encourage blood flow for faster healing, and restore your physical function and fitness level. The main aim of physical therapy is to make your daily activities, such as walking, getting in and out of bed and climbing stairs, easier.
The gluteus medius is one of the major muscles of the hip; essential for the movement of the lower body and keeping the pelvis level during ambulation. The gluteus medius muscle arises from the top of the pelvic bone and attaches to the outer side of the thighbone or femur at the greater trochanter by the gluteus medius tendon.
Arthroscopy, also referred to as keyhole or minimally invasive surgery, is a procedure in which an arthroscope is inserted into a joint to check for any damage and to repair the problem at the same time. An arthroscope is a small, fiber-optic instrument consisting of a lens, light source, and video camera.
Hip replacement is a surgery performed to replace parts of a diseased hip joint with a prosthesis. The goal of hip replacement is to eliminate pain and enable you to return to your normal activities. You can help in the recovery and improve the outcomes of the procedure by following certain precautions and changing the way you carry out your daily activities.
Physical examination of the hip is the key component in diagnosing the cause of your hip pain or hip pathology. The physical examination of the hip by your doctor includes a visual inspection of your hip, palpation of the hip to diagnose tenderness or any abnormality, etc; and testing range of motion of the hip.