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 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. These conditions are referred to as inflammatory arthritis.
Hip instability can be traumatic or atraumatic. Traumatic instability can be caused by injuries from sports or motor vehicle accidents. These injuries can damage the bony structures, labrum, and cartilage of the hip joint and form loose bodies. It can range from severe dislocation to a simple subluxation (partial displacement) of the hip joint.
The hip joint is one of the most important and flexible joints in the human body which allows us to walk, run, bend and perform physical activities. It is a ball (femoral head) and socket joint formed between the hip bone and femur (thighbone). It is surrounded by strong muscles and tough ligaments that prevent its dislocation.
The femur or thigh bone is the longest and strongest bone in the body, connecting the hip to the knee. A femur fracture is a break in the femur. The distal femur is the lower part of the thigh bone which flares out like an upside-down funnel and its lower end is covered by a smooth, slippery articular cartilage that protects and cushions the bone during movement.
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.
Hip replacement is a surgical procedure in which the damaged cartilage and bone are removed from the hip joint and replaced with artificial components. Any resulting fractures or breaks in the bone around the implant are called periprosthetic hip fractures. They usually occur around the stem of the implant and sometimes to the socket (acetabulum).
Hip osteonecrosis occurs due to disruption of the blood supply to the highest part of the thigh bone (femoral head). Due to lack of nourishment, the bone tissue of the femoral head dies and gradually collapses, which may further lead to degeneration of the underlying cartilage.
Robotic anterior total hip arthroplasty is a minimally invasive surgical procedure that involves the use of a specialized robotic system to remove the damaged parts of a hip joint and replace them with an artificial prosthesis or implant from an anterior approach rather than a traditional total hip arthroplasty approach.
For a successful total hip replacement, accurate positioning of the implants is crucial to accomplish a good clinical outcome. Computer-navigated total hip replacement is an advanced technology developed to provide more accurate positioning of an implant.
Hip replacement surgery is one of the most common orthopedic surgeries performed. It involves the replacement of the damaged hip bone (ball shaped upper end of the femur) with a ceramic ball attached to a metal stem that is fixed into the femur and placing a new cup with a special liner in the pelvis.
Anterior hip replacement surgery is performed under general anesthesia or regional anesthesia. You will lie down on your back, on a special operating table that enables your surgeon to perform the surgery from the front of the hip. Your surgeon may use fluoroscopic imaging during the surgery to ensure the accuracy of component positioning and to minimize leg length inequality.
Posterior hip replacement is a minimally invasive surgical procedure in which the worn out or damaged surfaces of the hip joint are removed and replaced with artificial joint components made of metal, ceramic, or plastic. It is also referred to as muscle sparing surgery because key muscles and tendons are left intact while accessing the hip joint, enabling a quicker return to normal activity.
Custom total hip replacement, also called bespoke hip replacement or patient-specific hip replacement, is a newer, more advanced technology in total hip arthroplasty that uses an individualized hip implant for the replacement of the damaged or injured components of the hip joint.
During total hip replacement, the damaged cartilage and bone are 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.
Revision hip replacement surgery is performed under general anesthesia. During the procedure, your surgeon will make an incision over the hip to expose the joint. Then, the femur is dislocated from the acetabulum so that the old plastic liner and metal socket can be removed from the acetabulum.
Reoperation of a total hip replacement to resolve a painful hip condition arising out of a damaged or worn out prosthesis (artificial hip joint) is known as correction of a failed hip replacement. During this corrective surgery, a partial or complete exchange of the prostheses that were implanted during the original surgery is done.
Hip fractures involve a break that occurs near the hip in the upper part of the femur or thigh bone. The thigh bone has two bony processes on the upper part - the greater and lesser trochanters. The lesser trochanter projects from the base of the femoral neck on the back of the thigh bone.
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.
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.
Exercising the muscles that surround and support the hip help restore range of motion and joint strength after hip replacement surgery. To ensure a positive surgical outcome, you are recommended to perform physical therapy exercises 2-3 times a day and walk for 30 minutes every day.