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 thighbone 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 of the Hip
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 thighbone 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 that surround and support the hip joint.
The head of the femur rotates and glides within the acetabulum. A fibrocartilaginous lining called the labrum is attached to the acetabulum and further increases the depth of the socket.
The femur is one of the longest bones in the human body. The upper part of the thighbone 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 of the Hip Joint
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 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 fibres that arise from the ischium behind the acetabulum and merge with the fibres 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 of the Hip Joint
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:
- Gluteal: 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 in the thighs which help in adduction, the action of pulling the leg back towards the midline.
- Iliopsoas: This muscle is 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 are also called 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 backwards.
Nerves and Arteries of the Hip Joint
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 the anatomical parts of the hip work together to enable various movements. Hip movements include flexion, extension, abduction, adduction, circumduction, and hip rotation.
Hip pain, one of the common symptoms that patients complain of, may not always be felt precisely over the hip joint. Pain may be felt in and around the hip joint and the cause for pain is multifactorial. The exact position of your hip pain suggests the probable cause or underlying condition causing pain. Pain felt inside the hip joint or your groin area is more likely to be because of the problems within the hip joint. Likewise, the pain felt on the outer side of your hip, upper thigh or buttocks may be a result of the problems of the muscles, ligaments, tendons and soft tissues surrounding the hip joint. However, certain disease conditions affecting other parts of your body such as lower back or knees also cause hip pain.
Osteoarthritis, also called degenerative joint disease, is the most common form of arthritis. It occurs most often in older people. This disease affects the tissue covering the ends of bones in a joint (cartilage). In a person with osteoarthritis, the cartilage becomes damaged and worn out causing pain, swelling, stiffness and restricted movement in the affected joint. Although osteoarthritis may affect various joints including hips, knees, hands, and spine, hip joint is most commonly affected. Rarely, the disease may affect the shoulders, wrists and feet.
Inflammation of the joints is referred to as arthritis. The inflammation arises when the smooth covering (cartilage) at the end surfaces of the 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. These conditions are referred to as inflammatory arthritis.
The hip joint is a ball and socket joint. The “ball” is the head of the femur, or thighbone, and the “socket” is the cup shaped acetabulum. The joint is surrounded by muscles, ligaments, and tendons that support and hold the bones of the joint in place. Hip dislocation occurs when the head of the femur moves out of the socket. The femoral head can dislocate either backward (posterior dislocation) or forward (anterior dislocation).
Hip joint injections involve injecting medicine directly into the hip joint to diagnose the source of pain or treat pain due to conditions such as arthritis, injury or mechanical stress of the hip joint. Hip pain may be experienced in the hip, buttock, leg or low back. The injection contains a combination of a numbing medicine and cortisone (an anti-inflammatory agent). Numbing medicine delivers temporary relief from pain, provided the hip joint is the source of the pain. It thus serves a diagnostic function and helps to confirm or deny whether the joint is the source of pain. Cortisone serves to reduce the inflammation in the joint providing long term pain benefit.
Arthritis is inflammation of the joints resulting in pain, swelling, stiffness and limited movement. Hip arthritis is a common cause of chronic hip pain and disability.
Revision hip replacement is a complex surgical procedure in which all or part of a previously implanted hip-joint is replaced with a new artificial hip-joint. Total hip replacement surgery is an option to relieve severe arthritis pain that limits your daily activities. During total hip replacement, the damaged cartilage and bone is removed from the hip joint and replaced with artificial components. At times, hip replacement implants can wear out for various reasons and may need to be replaced with the help of a surgical procedure known as revision hip replacement surgery.
Hip fractures refer to any kind of breakage or damage in the thighbone (femur). People over the age of 65, especially women, are highly vulnerable to hip fractures. You will require assistance after hip fractures from family members as well as health professionals and may also be required to be admitted to the hospital for further assistance. Hip fractures can be caused due to weak bones (osteoporosis) or from a fall. Osteoporosis is due to various factors such as age, gender, nutrition, life style or heredity.
Hip replacement is a surgery performed to replace parts of a diseased hip joint with an artificial prosthesis. The goal of hip replacement is to eliminate pain and return you to your normal activities. You can help in recovery and improve the outcomes of the procedure by following certain precautions and changing the way you carry out your daily activities.