The miracle surgery which helps the lame walk may have its price. New evidence shows that metallic debris from the replaced joints travels to other organs, possibly causing cancer.
There is no doubt that replacing the cartilage of hip or knee joints (worn away by osteoarthritis) with an artificial joint has transformed the life of many older people who would otherwise be confined to a wheelchair.
Hip replacement is now thought to be the most common form of surgery in the UK (more than 45,000 operations were performed in 1991 (The Guardian, February 23, 1993). Approximately 120,000 knee replacements are performed annually in America (N Eng J Med, 1990; 323: 801-807). And it's undoubtedly big business. The cost of performing these operations was estimated at $3.5 billion in 1990 (JAMA, May 4, 1994).
However, there's a catch. You might not think such a commonly performed operation could turn into a walking time bomb, but varying surgical standards (JAMA, May 4, 1994; 271, No 17: 1349) and the use of unproven materials are being blamed for hip replacements wearing out and a wide range of life threatening side effects from chronic infection to cancer and thrombosis.
In the last decade, the number of first time failures requiring surgical revision has trebled to 12 per cent. One in 90 patients who undergoes a total hip replacement will die. One in every 35 is re-admitted to hospital as an emergency within a month of the operation (BMJ, December 7, 1992). An overall analysis of knee replacements in America shows a complication rate running at 18 per cent. Infections and a blockage in the lung (pulmonary embolism), or blood clot in the vein, are cited as the most common complications (Rev de Chir Orth et Rep de l'App Mot, 1993; 79 (7): 577-585). A stroke caused by a pulmonary embolism remains the most common cause of death in patients undergoing knee replacements (JAMA, June 8, 1994; and Lancet, April 24, 1993).
Bio material failure is a frequent cause, with the metal titanium a particular culprit (Orthopedics, Nov 1993). When used in an artificial hip, titanium is generally combined with two other metals vanadium and aluminium. But this mixture is too soft for use as a bearing surface, and the materials have been shown to break down, sending particles into the body (Amer J of Surg Path, Jan 1994). The long term effects of this process remain unknown, although new evidence shows that high levels of microscopic potentially carcinogenic debris (generated through surface friction as the replacement grinds against the bone, or by simple corrosion) migrate to the body's major organs.
The Bristol Wear Debris team, a group of analysts based in England, have carried out a post mortem comparison of patients with and without metal implants from joint replacement surgery. High levels of debris in the liver, lymph glands (Annales de Rad, 1993; 36 (2): 114-117), bone marrow and spleen were discovered in samples taken from patients with stainless steel and cobalt chrome implants ( J of Bone & Joint Surg, September 1994). But the highest number of particles were taken from within patients whose joint replacements were considered to be loose and worn. Most of the debris came from the joint's matt coating (J of Bone Joint Surg, Nov 1993). The level of cobalt found in one patient's bone marrow was several thousand times that considered to be normal (Amer J of Surg Path, Jan 1994).
Although the researchers at Bristol have not yet proved a link with the disease, they have reported that the accumulation of these metallic particles is associated with chronic inflammation (Orth Rev, May 1994), lymph node disease, the destruction of bone marrow, bone resorption and a loosening of the implant.
"There is concern," they write guardedly, "that metals used in prosthesis may cause neoplasia (cancer), since they are potentially carcinogenic in other
situations" (The Journal of Bone and Joint Surgery, September 1994).
The incidence of cancer in 433 hip
replacement patients operated on between 1967 and 1973 shows the risk of site specific cancer increased. The use of chrome cobalt molybdenum alloy as a possible cause requires further investigation (Orth, Feb 1991).
The London Bone Tumour Service has reported three cases where titanium alloy prostheses caused the formation of fluid filled cysts containing metallic debris (Clin Rad, April 1993).
Other complications include sciatic nerve palsy (SNP), regarded as one of the most distressing conditions associated with total hip replacement (J of Arth, Feb 1994). The retention of urine after the operation is another quite common problem, although the condition is usually treated with alpha blockers which of course are known to have worrying side effects (Clin Orth & Rel Res, Aug 1991).
Aggressive granulomatosis is a potentially devastating complication from joint replacement surgery, where there is a severe, allergic reaction to the implant material (Can Assoc of Rad J, Aug 1994). Knee replacement patients are also at high risk of developing deep venous thrombosis (DVT) in the calf (Br J of Rad, Mar 1993).
In the operation, the surgeon removes the damaged cartilage (soft lining of
the joint), plus a small amount of the
underlying bone. The artificial joint (made from metal and polyethylene) is cemented into place with acrylic cement. A patient with no complications will spend four to five days convalescing in the hospital, followed by a month at home. He can return to regular walking and activity over the next two to three months.
Or so it says in the textbook and when the operation is sold to you as a patient. However, a problem arises when the
current tried and tested technology reaches the end of its natural life. Replacing the replacement is a complex operation being performed more and more, which involves bone loss and the removal of scarred tissue.
As the number of hip and knee replacements is growing, so is the number of operations to replace the replacements that have become infected, an expensive procedure whose cost is creating a strong incentive for surgeons to avoid infection in the first place (Curr Op in Rheum, Mar 1994). It has also been suggested that second operations for failed replacements should be performed by specialist centres because of the unsatisfactory track record of repeat operations (Uges for Laiger, Sept 6, 1993).
Infection is a problem in all forms of surgery, but with an operation as radical as total hip replacement, the risk is multiplied: "If there is infection, then the operation is a complete failure," says Mike Wroblewski, successor to John Charnley, who pioneered the operation at the Wrightington Hospital in Wigan over 30 years ago.
The effects of infection during a hip or knee replacement can be devastating and lead to a loss of function, amputation, even death (Curr Op in Rheum, May 1993). Associations have also been made between oral infection and subsequent blood infection after total joint replacement operations (BMJ, Aug 20-27, 1994), particularly if the patients have periodontal disease. Nevertheless, few doctors take the same precautions with hip replacement patients that they do with heart valve patients who receive antibiotic treatment with oral surgery (British Medical Journal, 12 October 1994).
The Royal Orthopedic Hospital in Birmingham, England has shown that 91 per cent of patients who received the Charnley hip replacement (the stem, ball and cup device named after John Charnley) still had them in place after 10 years with 82 per cent after 20 years (BMJ, Feb 1).
Nevertheless, a enormously lucrative market has grown up. For some time now, medical technology firms have been trying to get round the wear out problem by fixing artificial joints to the bone biologically by using small metal beads, or mesh. These products called "uncemented porous coated" knee replacements have proved not to be as successful as the cemented variety (J of Bone & Joint Surg, Aug 1994).
In one of the many studies demonstrating this in the Journal of Bone and Joint Surgery (July 1991), of the 96 patients undergoing 108 knee replacements, around a fifth had also failed more often because of problems with the replacement's tibial (lower leg bone) component. After seven years, more than half the replacements had been recommended for revision. A Swedish study which examined the success rate of these devices in hip replacements found only a quarter could survive (Acta Orth Scand Supp, 1990).
Many orthopedic surgeons complain that many of these so called "designer hips" are not tested properly before they're released on to the market. Manufacturers are continually introducing new models, although their largely
theoretical claims for these supposedly improved products remain unproven and are often quietly withdrawn, claims Dr Chris Bulstrode, an orthopedic
surgeon at the John Radcliffe Hospital, Oxford, England (BMJ, March 20, 1993): "You can design a hip replacement in your garden shed today and be putting it into patients tomorrow," he says (Guardian, February 23, 1993).
In 1971, the Charnley design was the only artificial hip available. Twenty or so years later, 34 varieties have flooded the market. Fellow surgeons, says Bulstrode, are too willing to accept the inducements that go with designer hips: "There's more money in design than success rates," he continues. "Every year there's a new colour, a new shape, a new coating."
It's the same with knee replacements. Development of the current technology began in the 1950s, and there are
now hundreds of prosthetic designs available.
To counter the hype of profit motivated manufacturers, orthopedic doctors are calling for better monitoring of the long term outcome of hip replacement operations. This would include the setting up of a national register of patients and the development of a more sophisticated measure of failure other than the current one which simply records the number of patients who need to have their operation repeated.