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hip replacement is a surgical procedure in which the hip joint is replaced by a prosthetic implant. Hip replacement surgery can be performed as a total replacement or a hemi (half) replacement. Such joint replacement orthopaedic surgerygenerally is conducted to relieve arthritis pain or fix severe physical joint damage as part of hip fracture treatment. A total hip replacement (total hip arthroplasty) consists of replacing both the acetabulum and the femoral head whilehemiarthroplasty generally only replaces the femoral head. Hip replacement is currently the most common orthopaedic operation, though patient satisfaction short and long term varies widely.
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).[1]
In 1940 at Johns Hopkins hospital, Dr. Austin T. Moore (1899–1963), an American surgeon, reported and performed the first metallic hip replacement surgery. The original prosthesis he designed was a proximal femoral replacement, with a large fixed head, made of the Cobalt-Chrome alloyVitallium. It was about a foot in length and it bolted to the resected end of the femoral shaft (hemiarthroplasty). A later version of Dr. Moore’s prosthesis, the so-called Austin Moore, developed in Columbia, SC was introduced in 1952 is still in use today, although rarely. Like modern hip implants it is inserted into the medullary canal of the femur. It depends on bone growth through a hole in the stem for long term attachment.
In 1960 a Burmese orthopaedic surgeon, Dr. San Baw (29 June 1922 – 7 December 1984), pioneered the use of ivory hip prostheses to replace ununited fractures of the neck of femur when he first used an ivory prosthesis to replace the fractured hip bone of an 83 year old Burmese Buddhistnun, Daw Punya.[2] This was done while Dr. San Baw was the chief of orthopaedic surgery at Mandalay General Hospital in Mandalay, 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 Orthopaedic 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 a bicycle and play football a few weeks after their fractured hip bones were replaced with ivory prostheses. Ivory may have been used because 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 Orthopaedic Association’s Conference in 1969, is published in Journal of Bone and Joint Surgery (British edition), February 1970. With modern hip replacement surgery, one can expect to walk immediately post-op.
The replacement joint, which was known as the Low Friction Arthroplasty, was lubricated with synovial fluid. The small femoral head (7/8″ (22.2 mm)) was chosen for Dr. Charnley’s belief that it would have lower friction against the acetabular component and thus wear out the acetabulum more slowly. Unfortunately, the smaller head dislocated more easily. Alternative designs with larger heads such as the Mueller prosthesis were proposed. Stability was improved, but acetabular wear and subsequent failure rates were increased with these designs. The Teflon acetabular components of Dr. Charnley’s early designs failed within a year or two of implantation. This prompted a search for a more suitable material. A German salesman showed a polyethylene gear sample to Dr. Charnley’s machinist, sparking the idea to use this material for the acetabular component. The Ultra High Molecular weight Polyethylene or UHMWPE acetabular component was introduced in 1962. Dr. Charnley’s other major contribution was to use polymethylmethacrylate (PMMA) bone cement to attach the two components to the bone. For over two decades, the Charnley Low Friction Arthroplasty, and derivative designs were the most used systems in the world. It formed the basis for all modern hip implants.
The Exeter hip stem was developed in the United Kingdom during the same time as the Charnley device. This is also a cemented device, but with a slightly different stem geometry. Both designs have shown excellent long-term durability when properly placed and are still wisely used in slightly modified versions.
Early implant designs had the potential to loosen from their attachment to the bones, becoming painful typically ten to twelve years after placement. In addition to the devices loosening, erosion of the bone around the implant was seen on x-rays. Initially surgeons believed this was caused by an abnormal reaction in response to the cement holding the implant in place. That belief prompted a search for an alternative method to attach the implants. The Austin Moore device had a small hole in the stem into which bone graft was placed before implanting the stem. It was hoped bone would then grow through the window over time and hold the stem in position. Success was unpredictable and the fixation not very robust. In the early 1980s, surgeons in the United States applied a coating of small beads to the Austin Moore device and implanted it without cement. The beads were constructed so that gaps between beads matched the size or the pores in native bone. Over time, bone cells from the patient would grow into these spaces and fix the stem in position. The stem was modified slightly to fit more tightly into the femoral canal, resulting in the Anatomic Medullary Locking (AML) stem design. With time, other forms of stem surface treatment and stem geometry have been developed and improved.
Initial hip designs were made of a one-piece femoral component and a one-piece acetabular component. Current designs have a femoral stem and separate head piece. Using an independent head allows the surgeon to adjust leg length (some heads seat more or less onto the stem) and to select from various materials from which the head is formed. A modern acetabulum component is also made up of two parts: a metal shell with a coating for bone attachment and a separate liner. First the shell is placed. Its position can be adjusted, unlike the original cemented cup design which are fixed in place once the cement sets. When proper positioning of the metal shell is obtained, the surgeon may select a liner made from various materials.
To combat loosening caused by polyethylene wear debris, hip manufacturers developed improved and novel materials for the acetabular liners. Ceramic heads mated with regular polyethylene liners or a ceramic liner were the first significant alternative. Metal liners to mate with a metal head were also developed. At the same time these designs were being developed, the problems that caused polyethylene wear were determined and manufacturing of this material improved. Highly-crosslinked UHMWPE was introduced in the late 1990s. The most recent data comparing the various bearing surfaces has shown no clinically significant differences in their performance. Potential early problems with each material are discussed below. Performance data after 20 or 30 years may be needed to demonstrate significant differences in the devices. All newer materials allow use of larger diameter femoral heads. Use of larger heads significantly decreases the chance of the hip dislocating, which remains the greatest complication of the surgery.
To date, when currently available implants are used, there is no demonstrable difference in performance of cemented versus uncemented stems, and no significant difference in the clinical performance of the various methods of surface treatment of uncemented devices. Uncemented stems are selected for patients with good quality bone that can resist the forces needed to drive the stem in tightly. Cemented devices are typically selected for patients with poor quality bone who are at risk of fracture during stem insertion. Cemented stems are less expensive due to lower manufacturing cost, but require good surgical technique to place them correctly. Uncemented stems can cause pain with activity in up to 20% of patients during the first year after placement as the bone adapts to the device. This is rarely seen with cemented stems.
Once an uncommon operation reserved for frail patients with a limited life expectancy, hip replacement is now common, even among active athletes including race car drivers Bobby Labonte and Dale Jarrett, and British Open runner-up, golfer Tom Watson.