Implant for Knee and Hip Repair

More and more people in the Western World are walking around with artificial hips and knees and aging baby boomers are leading the way. That is partly because excess weight is fraying their joints earlier. Between the years 2000 and 2006, knee replacements shot up by 65 percent. 

Hip and knee replacements get high marks for relieving arthritis pain. Though the procedures can have serious complications and don’t always restore perfect mobility, more than 80 percent of people said they were satisfied with their new joints, according to a Consumer Reports survey. And since then, advances in pain control and rehabilitation have sped recovery. 

But the increase in younger patients, who will eventually outlive their artificial joints, poses challenges. Manufacturers have engineered new implants that last longer in the laboratory than traditional ones, but none has been tested long enough to know how they will perform beyond 10 or 20 years in real life. Yet the implants, as well as several controversial surgical procedures, have been heavily advertised to consumers and rapidly accepted into practice.

As hip and knee implants are somewhat similar to dental implants, I thought it would be interesting to get familiarized with that type of surgery.

Why good joints go bad 

The most common cause of hip and knee damage is osteoarthritis, which means the erosion of cartilage between the joints that allows adjoining bones to rub together. Joints damaged by rheumatoid arthritis, a less common but more serious disorder, can be replaced as necessary when medical treatment has failed. The need for joint replacement can often be delayed by the use of pain relievers, losing excess weight, and by doing regular low-impact exercises such as tai chi. The Arthritis Foundation website (www.arthritis.org) has information on choosing the right exercise for you to help relief arthritis pain. 

But when the damage is advanced, joint replacement becomes a good option. In knee replacement, surgeons remove damaged portions of the thighbone, shinbone or kneecap and insert artificial parts, generally using cement to help keep them in place. In hip replacement, they cut off the head of the thighbone, or femur, and hollow out its shaft. Then they insert a new hip socket and a new femoral head, anchored by a stem that’s wedged into the shaft, usually without cement. In either operation, the parts are usually made of metal and polyethylene, a plastic. They can last 20 years, but they wear out earlier in younger, heavier, and more active people. 

The most common reason hip and knee implants fail is loosening. As metal and plastic rub together, the friction wears away the surfaces, creating tiny plastic particles around the joint. The body attempts to remove those particles but in the process removes bone as well, causing the implant to loosen. The joint then has to be replaced, a procedure known as revision surgery, which is usually less successful than the original operation because of the bone loss. 

New parts for old bones 

Manufacturers have addressed the loosening problem by developing new devices. But each has drawbacks. Many patients base their choice on advertising. But it is recommended to find a physician instead who is knowledgeable about the issues and make a collaborative decision. 

	Metal on highly cross-linked polyethylene	Metal on metal	Ceramic on ceramic
Use	Knees and hips.	Hips only.	Hips only.
Plus	This new plastic wears substantially less than conventional polyethylene.	It wears less than metal on plastic, and offers a larger femoral head, reducing the chance of dislodgment.	It’s likely to wear out the slowest.
Minus	It has a shorter track record and might be more prone to fracture.	It releases metal particles into the bloodstream that have unknown effects on the body and are particularly worrisome in women of childbearing age. Moreover, a few patients have developed allergies to the metal debris.	It poses a rare but serious risk of chipping or braking. Moreover, up to 7 percent of patients have complained of squeaky ceramic hips.
Advice	It offers durability with the fewest side effects, making it the best choice for most people. But because the knee puts greater demand on the joint, increasing the risk of fracture, physicians generally recommend metal on conventional polyethylene for knee replacements.	This kind of device might make sense for young men in need of hip replacement whose work involves heavy labour, which increases the risks of joint dislocation and wear.	This might be an option for patients who need to get many decades out of their hip, such as very young men, or women of childbearing age.

 

A smaller cut 

Some surgeons now use a technique called minimally invasive surgery, which might limit damage to muscle and tissue. The potential advantages are faster recovery and reduced pain – but at the cost of longer operative time and a high risk of surgical errors, including incorrect implant positioning, nerve injury, and bone fracture. The benefits of the procedure are still being debated, but marketing claims have fuelled patient demand. Many surgeons feel they need to offer it or they’ll lose patients to someone else. But the scientific evidence that this technique makes a substantial difference is lacking. 

In fact, improvements in pain control and rehabilitation appear to speed recovery in hip-replacement patients whether they have small or conventional incisions, according to a 2007 study published in the Journal of Bone and Joint Surgery. Physicians note the same effect in knee patients. 

Many surgeons now use “mini” cuts that are significantly smaller than traditional incisions but large enough for them to view the operating field. Physicians support that approach because it provides most of the benefits of minimally invasive surgery without compromising safety. But they note that large-boned patients still require larger incisions, as do those who are overweight, have a joint deformity, or have had prior surgery on the joint. 

Hip resurfacing 

Aimed at younger patients who want to delay total hip replacement, this procedure removes only the damaged joint surfaces. The socket is replaced with a metal cup and the femoral head is shaved down and covered by a metal cap anchored by a short stem. That preserves more of the thighbone, making future revision surgery easier. 

“Patients read marketing materials and want this procedure. But the appeal of preserving bone can lead to false expectations.” 

Women who had resurfacing are twice as likely to need early revision than those receiving regular hip implants, chiefly due to femoral neck fractures. Women might be at higher risk for such fractures because their bones are smaller and weaken at menopause. 

Additional concerns include the complexity of the operation and metal-on-metal debris. Some surgeons avoid the procedure altogether, others recommend it only for younger men, and some propose it for strong-boned patients regardless of gender. But most agree that resurfacing is not advisable in patients who are likely to have weak bones – such as postmenopausal women, people over age 65, or those who score poorly on bone-density tests. 

Partial knee replacement 

In this procedure surgeons replace only the eroded side of the knee. Compared wit h total knee replacement, it offers a smaller incision, faster recovery, and superior function. Moreover, it might buy patients 10 to 15 years before they need total knee replacement. 

But the operation isn’t as durable or predictable as total knee replacement. In the same British study, which looked at more than 80,000 knee patients, early revision rates were twice as high for those who had partial knee replacement, especially among younger patients. Common reasons for failure include loosening and arthritis in other parts of the knee. 

“Partial knees are great in the right person. But only one in 20 people who need knee replacement are candidates.” Patients should have arthritis in only one side of the knee, intact ligaments, and good range of motion. In addition, they can’t be very heavy, nor too bowlegged or knock-kneed.

In french: Implants pour hanches et genoux