Total Hip Replacement (THR)

Total hip replacement (also known as total hip arthroplasty), which was first performed in 1960, is a surgical procedure in which the damaged cartilage and bone is removed from the hip joint and replaced with artificial components. Since 1960, improvements in joint replacement surgical techniques and technology have greatly increased the effectiveness of total hip replacement, and it is one of the most successful operations in all of medicine, with satisfaction rates reported of about 95%. Hip replacement surgery is a relatively safe procedure that can predictably relieve pain, increase motion, and help you return to enjoying normal, everyday activities.

Anatomy

The hip is one of the body's largest weight-bearing joints. It is a ball-and-socket joint, with the socket formed by the acetabulum (which is part of the large pelvis bone) and the ball is the femoral head (which is the upper end of the femur or thighbone). The bone surfaces of the ball and socket are covered with articular (hyaline) cartilage, a smooth tissue that cushions the ends of the bones and enables them to move smoothly. A thin tissue called synovial membrane surrounds the hip joint, and in a healthy hip, this membrane makes a small amount of fluid that lubricates the cartilage and eliminates almost all friction during hip movements. Bands of tissue called ligaments as well as the hip capsule connect the ball to the socket and provide stability to the joint.

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Normal hip anatomy

Causes of Hip Arthritis

Any process that can damage the protective smooth layer of joint surface cartilage may lead to osteoarthritis, causing extreme pain and difficulty in performing daily activities. The exact cause of osteoarthritis is not known, and there is currently no medical cure. All non-surgical (conservative) therapies aim to manage the disease and relieve symptoms. Joint replacement surgery is the only real solution for symptomatic end-stage arthritis.  

There are a number of diseases and conditions that may cause damage to the articular cartilage resulting in arthritis, and these include:

• Osteoarthritis – This is the most common form of hip arthritis. It is an age-related "wear and tear" type of arthritis, and usually occurs in people 50 years of age and older and often in individuals with a family history of arthritis. Over time, the joint cartilage cushioning the bones of the hip becomes thinner or completely absent exposing bare bone. In addition, the bones become thicker around the edges of the joint and may form bony “spurs” (osteophytes). These factors can cause pain, swelling and restriction in hip movement.
• Inflammation of the joint (inflammatory arthritis – the commonest being rheumatoid arthritis) – Rheumatoid arthritis is an autoimmune disease in which the tissue lining the joint (synovial membrane) becomes inflamed and thickened with production of excessive joint fluid containing destructive enzymes and factors. This chronic inflammation can damage the cartilage, leading to pain and stiffness. 
• Post-traumatic arthritis - This results from a hip injury (such as a previous labral tear or chondral injury), fracture, or traumatic dislocation.
• Avascular necrosis – In avascular necrosis (also commonly referred to as "osteonecrosis"), the blood supply to the head of the femur is lost or restricted, and may cause death of the bone with collapse of the hip joint surface, and secondary arthritis develops. An injury to the hip, such as a dislocation or fracture, may limit the blood supply to the femoral head. And there are a number of specific associated factors (e.g. excess alcohol or longer term use of steroids) and diseases that will also precipitate avascular necrosis (see the section on Hip Avascular Necrosis).
• Childhood hip disease - Some infants and children have hip problems. Even though the problems appear to have been successfully treated during childhood, they may still cause arthritis later on in life. This happens because the hip may not grow normally, and the joint surfaces are affected by the changes in the patterns of force applied. Some of these conditions include developmental hip dysplasia (DDH), Perthes disease, or slipped capital femoral epiphysis (where the round growing part of the femoral head slides of the neck of the femur).
• Increased body weight.
• Repetitive overuse – Probably secondary to recurrent labral or chondral surface injury.
• Joint infection (septic arthritis) – The bacterial infection leads to rapid joint surface cartilage destruction.  This is an orthopaedic emergency.  Delay in management will inevitably cause irreversible joint damage and secondary arthritis, requiring hip replacement once the area has been sterilised (infection eradicated).
• Connective tissue disorders (such as systemic lupus erythematosus).

Indications for Total Hip Replacement

Total hip replacement surgery is commonly indicated for severe osteoarthritis of the hip that has failed to respond to non-surgical treatments. 

A number of diseases and conditions can cause damage to the articular (joint surface) cartilage that result in hip pain and disability, with osteoarthritis, rheumatoid arthritis, and post-traumatic arthritis being the most common.

In hip osteoarthritis, the smooth articular cartilage wears away and becomes frayed and rough, with secondary joint space narrowing, formation of bone spurs.

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Total hip replacement may be advised if you have:

• Hip pain that limits everyday activities, such as walking or bending
• Hip pain that continues while resting, either day or night
• Stiffness in a hip that limits the ability to move or lift the leg
• Inadequate pain relief from conservative (non-surgical) treatments including anti-inflammatory drugs, physical therapy, or walking supports

Recommendations for surgery are based on a patient's pain and disability, and not their age. Most patients who undergo total hip replacement are aged 50 to 80, but each patient must be individually evaluated. Total hip replacements have been performed successfully at all ages, from the young teenager with juvenile chronic arthritis to the elderly patient with degenerative osteoarthritis.

With current generation technology, techniques and implants, the total hip prosthesis should last over 20 years.

Description

During a total hip replacement (also called total hip arthroplasty), the damaged bone and cartilage is removed and replaced with prosthetic (artificial) components. The steps involved include:

• The damaged femoral head is removed and replaced with a metal stem that is inserted into the hollow centre (marrow in the canal) of the femur. The femoral stem may be either cemented or "press fit" (uncemented) into the bone.
• A metal or ceramic ball is impacted on the upper part of the stem. This ball acts as a substitute for the damaged femoral head that was removed.
• The damaged cartilage surface of the socket (acetabulum) is removed and replaced with a metal socket (shell). Screws or cement (cement is usually only used with all-plastic sockets) are sometimes used to hold the socket in place.
• A plastic, ceramic, or metal spacer (liner) is inserted into the acetabular shell to allow for a smooth gliding surface.