The Advent of Total Hip Replacement

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The Advent of Total Hip Replacement

Overview

In 1961 John Charnley (1911-1982) developed successful surgery for replacing diseased or injured hip joints with artificial joints. Many surgeons consider total hip replacement (THR) the greatest surgical advance of the second half of the twentieth century, because it has dramatically improved the quality of millions of lives and is relatively free of complications.

Background

The skeletal system gives the body shape, strength, and structure. Generally, it is durable enough to do this, except for a few troublesome areas, particularly the movable joints, which are the weakest parts of the skeleton. Joints, especially the hips and knees but also the shoulders, elbows, wrists, knuckles, and ankles, deteriorate with age, are easily injured, and are commonly subject to debilitating chronic diseases such as arthritis. Joint diseases and injuries have caused agony and disability since the beginning of time, but until the 1950s there was little that doctors could do to help. The best remedy for a diseased or injured joint is to replace it altogether, but that became technologically possible only through Charnley's work.

The human pelvis on each side contains a cup or socket called the "acetabulum." The ball-and-socket hip joint is formed by the head of the femur rotating in the acetabulum, lubricated by synovial fluid, supported by ligaments and muscles, and cushioned by cartilage. The head of the femur is connected to the shaft by the neck. Between the neck and shaft of the femur are two protuberances, the greater (outer) and lesser (inner) trochanters.

Any artificial body part is a "prosthesis." This could be anything from a wooden leg to a plastic heart valve to a set of dentures. Surgery to replace a natural joint with a prosthesis is "arthroplasty," from the Greek words arthron ("joint") and plassein ("to form, to shape, or to create"). The surgeon literally creates a new joint. Arthroplasty can also mean rebuilding a joint without using a prosthesis.

The first successful arthroplasty was performed at Pennsylvania Hospital, Philadelphia, in 1826 by John Rhea Barton (1794-1871), who reported the case as "On the Treatment of Anchylosis by the Formation of Artificial Joints," in The North American Medical and Surgical Journal. Ankylosis is the pathological stiffening of a joint. A 21-year-old sailor had fallen on his hip. Within a year of the injury the hip joint had become immovable and he had lost the use of his leg. The head of the femur had knitted into the acetabulum so that the pelvis and the femur were as one bone, with the leg turned inward.

Barton operated 20 months after the injury. He made a large cross-shaped incision centered over the greater trochanter, retracted the soft tissue, sawed through the femur transversely between the two trochanters, then returned the soft tissues to their place and closed the wound. Four months later, after intense physical therapy, the sailor was walking short distances without crutches.

Barton's arthroplasty did not involve the insertion of any prosthesis. He turned a disabled ball-and-socket joint into a functional hinge joint using only the bone, muscle, and ligaments of the disabled joint—and did it all in seven minutes. In the era before anesthesia surgeons had to work fast.

Barton's success was miraculous and isolated. The permanence of a fabricated joint with no natural connectives or lubrication could not be guaranteed, although Barton's sailor apparently overcame the improbable odds. Successful hip arthroplasty without prosthesis was reported by Royal Whitman (1857-1946) in 1924, but surgeons gradually came to understand that prostheses would be needed to achieve their goal of artificial joints with more inherent strength, more dependable structure, less friction, and greater endurance.

Modern hip prosthetic arthroplasty began in the 1920s. The femoral head was left alone, but an artificial cup was inserted into the acetabulum, mainly as a barrier against ankylosis or reankylosis. The first material used for the cup was glass (1923), but that was abandoned because it abraded or broke under the body's weight. A form of celluloid, viscaloid, was tried (1925), but the body tended to reject it. Pyrex then became the standard (1933), but problems remained with abrasion and breakage. Bakelite was used briefly (1937).

In 1937 at Harvard, Marius Nygaard Smith-Petersen (1886-1953) began experimenting with metals for acetabular cups. He built upon the work of Charles Scott Venable (1877-1961), Walter G. Stuck, and Asa Beach. He reported his design of a successful cup made of "Vitallium," a relatively inert, generally biocompatible alloy of cobalt, chromium, and molybdenum, patented by Charles H. Prange for Austenal Laboratories in 1934 and first used in dentistry.

The next major advance occurred when Jean Judet and Robert Louis Judet of Paris, France, developed a steel-reinforced acrylic femoral head. They reported in 1950 that this device reduced pain for 70% of patients and increased mobility for 90%, but two thirds of patients still needed a cane after the operation. The main problem with the Judet prosthesis was friction. The new joint sometimes even squeaked.

In 1938 Roy J. Plunkett invented polytetrafluorethylene (PTFE), a low-friction, nearly inert substance commonly known as "Teflon." In the 1950s Charnley experimented with Teflon acetabular cups and metal femoral heads to produce slippery, well-lubricated, and therefore longer lasting and less painful joints. His 1961 report of a successful operation marked the long-awaited breakthrough in low-friction prosthetic arthroplasty. For the first time both the acetabulum and the head of the femur could be replaced with artificial materials. This was the first genuine THR.

Impact

Total Hip Replacement has had a profound impact on the ability of the medical community to treat hip joint problems. As of 1994, 120,000 THR operations were being performed each year in the United States. Millions have been performed worldwide. Almost all patients receive distinct relief from their hip conditions. Sometimes re-operations are necessary to replace defective, deteriorated, or improperly installed implants, but the long-term prognosis for THR remains among the most optimistic for all surgical procedures. Rates of complication such as infection or induced thrombosis (blood clots) dropped significantly after the 1980s because of more effective prophylactic and anticoagulant drugs, earlier and more thorough physical therapy, and shorter hospital stays.

In 1950 40-year-old patients with degenerative hip disease might end up in wheelchairs by age 60. In 2000 similar patients, after THR, could be walking, playing golf, or cycling in their seventies and eighties.

One of the main problems with THR is the gradual disintegration of the materials of the artificial ball-and-socket joint. Early in the 1960s Charnley realized that Teflon was not adequate for the socket because it would erode and discharge irritating debris into the joint and surrounding tissues. His experiments with other synthetic low-friction materials led him in 1963 to high density polyethylene, which is still preferred by most THR surgeons.

Meanwhile, research in prostheses for other joints was advancing. In 1959 Earl W. Brannon and Gerold Klein reported the first successful prosthesis for a finger joint. A.B. Swanson introduced flexible silicone finger joint prostheses in 1966. Frank H. Gunston made major breakthroughs in knee replacement surgery in the 1960s and 1970s. Each type of joint presents its unique set of problems for researchers. The hip and knee are significantly different from other joints because of the tremendous load of weight and stress they must bear.

One controversy among THR surgeons is how to attach the prosthesis to the bone. The acetabulum is reamed and the cup prosthesis is inserted. The head and neck of the femur are removed either above or through the trochanters and the stem of the ball prosthesis is inserted into the shaft of the femur. The question is whether these components should be cemented to the residual bone or adhered in some cementless way. Bone will usually grow into a porous or roughened surface and create a strong bond without cement. On the other hand, bone cement may provide a stronger and more durable bond but may be more likely to cause infection or injury to surrounding tissues. Polymethylmethacrylate (PMMA) bone cement, introduced by Charnley in the early 1960s, is still the standard, but it sometimes loosens and generates debris. Whether to cement or not to cement often depends upon the age of the patient. Older patients, with thinner and weaker bones, often do better with cemented prostheses.

Debris control, friction control, and the bone/prosthesis bond remain areas of concern. Research into these problems generally centers around the materials used. Titanium, for example, was tried in the 1980s but proved too soft. David G. Murray, who chaired the prestigious U.S. National Institutes of Health Consensus Development Conference on Total Hip Replacement in 1994, prefers for the ball component an alloy of cobalt, chromium, and molybdenum with a porous or roughened femoral stem. Surgeons also use polished hardened ceramics such as alumina or zirconia for the head. The femoral stem is sometimes coated with another ceramic, hydroxyapatite, because it is chemically similar to bone and therefore adheres well without cement. With many minor improvements, ultrahigh molecular weight polyethylene for the socket has been used since Charnley's time, but methods of attaching it to the acetabulum vary. Acetabular components backed with porous ceramic-coated metal have so far shown the best results.

ERIC V.D. LUFT