Hip replacement
Hip replacement, also hip arthroplasty, is a surgical procedure in which the hip joint is replaced by a prosthetic implant. Such joint replacement surgery generally is conducted to relieve arthritis pain or fix severe physical joint damage.

# History
The earliest recorded attempts at hip replacement (Gluck T, 1891), which were carried out in Germany, used ivory to replace the femoral head (the ball on the femur). 
In 1960 a Burmese orthopaedic surgeon, Dr. San Baw (29 June 19227 December 1984), pioneered the use of ivory hip prostheses to replace ununited fractures of the neck of femur ("hip bones"), when he first used an ivory prosthesis to replace the fractured hip bone of an 83 year old Burmese Buddhist nun, Daw Punya.  This was done while Dr. San Baw was the chief of orthopeadic surgery at Mandalay General Hospital in Manadalay, Burma. Dr. San Baw used over 300 ivory hip replacements from the 1960s to 1980s. He presented a paper entitled "Ivory hip replacements for ununited fractures of the neck of femur" at the conference of the British Orthopeadic Association held in London in September 1969. An 88% success rate was discerned in that Dr. San Baw's patients ranging from the ages of 24 to 87 were able to walk, squat, ride the bicycle and play football a few weeks after their fractured hip bones were replaced with ivory prostheses. Ivory may have been used beacause it was cheaper than metal at that time in Burma and also was thought to have good biomechanical properties including "biological bonding" of ivory with the human tissues nearby.  An extract from Dr San Baw's paper, which he presented at the British Orthopeadic Association's Conference in 1969, is published in Journal of Bone and Joint Surgery (British edition), February 1970.

# Modern process
The modern artificial joint owes much to the work of John Charnley at Wrightington Hospital; his work in the field of tribology resulted in a design that completely replaced the other designs by the 1970s. Charnley's design consisted of three parts
- a metal (originally stainless steel) femoral component,
- a teflon acetabular component which was replaced by high molecular weight polyethylene in 1962, both of which were fixed to the bone using
- acrylic bone cement.
The replacement joint, which was known as the Low Friction Arthroplasty, was lubricated with synovial fluid. The small femoral head (7/8" (22.2mm)) was chosen for its decreased wear rate; however, this has relatively poor stability (the larger the head of a replacement the less likely it is to dislocate, but the more wear debris produced due to the increased surface area). For over two decades, the Charnley Low Friction Arthroplasty design was the most used system in the world, far surpassing the other available options (like McKee and Ring). Recently the use of a polished tapered cemented hip replacement (like Exeter) and uncemented hip replacements have become more popular. Once an uncommon operation, hip replacement is now common, even among active athletes including racecar drivers Bobby Labonte and Dale Jarrett.

# Costs
In a paper published August 14, 2007 in The Japan Times, signed by K. Rogoff, it is mentioned that 250.000 hip replacements are performed in the U.S. each year, for an average cost of $6.000.  However, that is quite contrary to what CNN-TV reported on Dec. 5, 2000, that the average cost of hip replacement surgery is $25,000.
Surgery costs vary from country to country, with the US typically being among the highest-priced markets, and countries like Thailand, Cuba and Argentina, among the lowest.

# Complications
In the short term post-operatively, infection is a major concern. Reported rates are about 1%. Deep infection will often require one or two stage revision surgery with an extended hospital stay and antibiotics. Recurrent dislocation is another indication for revision. The rate is also about 1%.
In the long term, many problems relate to osteolysis from wear debris. An inflammatory process causes bone resorption and subsequent loosening or fracture often requiring revision surgery. Very hard Ceramic bearing surfaces are being used in the hope that they will have less wear and less osteolysis with better long term results. Large metal heads are also used for similar reasons, these also have excellent wear characteristics and benefit from a different mode of lubrication. A greater head neck ratio also contributes to stability. These new prosthesis do not always have the long term results or reliability of established metal on poly bearings.

# Indications
Total hip replacement is most commonly used to treat joint failure caused by osteoarthritis. Other indications include rheumatoid arthritis, avascular necrosis, traumatic arthritis, protrusio acetabuli certain hip fractures, benign and malignant bone tumors, arthritis associated with Paget's disease, ankylosing spondylitis and juvenile rheumatoid arthritis. The aims of the procedure are pain relief and improvement in hip function. Hip replacement is usually considered only once other therapies, such as pain medications, have failed.

# Techniques
There are several different incisions, defined by their relation to the gluteus medius. The approaches are posterior (Moore),  lateral (Hardinge or Liverpool), antero-lateral (Watson-Jones), anterior (Smith-Petersen) and greater trochanter osteotomy. There is no compelling evidence in the literature for any particular approach, but consensus of professional opinion favours either modified anterio-lateral (Hardinge) or posterior approach.
- The posterior (Moore) approach accesses the joint through the back, taking piriformis muscle and the short external rotators off the femur. This approach gives excellent access to the acetabulum and preserves the hip abductors. Critics cite a higher dislocation rate although repair of capsule and SERs negates this risk.
- The lateral approach is also commonly used for hip replacement. The approach requires elevation of the hip abductors (gluteus medius and gluteus minimus) in order to access the joint. The abductors may be lifted up by osteotomy of the greater trochanter and reapplying it afterwards using cables (as per Charnley), or may be divided at their tendinous portion, or through the functional tendon (as per Hardinge) and repaired using sutures.
- The anterolateral approach develops the interval between the tensor fasciae latae and the gluteus medius.
- The anterior approach utilises an interval between the sartorius and tensor fascia latae.
The double incision surgery and minimally invasive surgery seeks to reduce soft tissue damage through reducing the size of the incision. However component positioning accuracy is impaired and surgeons using these approaches are advised to use computer guidance systems.

# Side effects
A few hip replacement patients suffer chronic pain after the surgery. Usually, X-ray and MRI cannot detect any problem with the hip joint replacement. Doctors do not know the source of the pain, or how to cure it. Generally, it is believed that such pain is caused by nerve damage during the replacement surgery.

# Research
Knowledge of the loads to which hip implants are subjected is a fundamental prerequisite for their optimal biomechanical design, long-term success, and improved rehabilitation outcomes. In vivo load measurements are made with instrumented implants and calculations by using mathematical musculoskeletal models which are performed at different research laboratories such as at the Benjamin Franklin Campus at the Berlin University.-8|]]