Hip Science: Better Bone Implants

ke4roh writes "Space, medicine, and invention often cross paths. In this case, the invention is a new artificial hip. Scientists are researching ways to manufacture strong and porous ceramics with the benefit of microgravity - subtracting the effects of convection and settling from their experiment. In the end, they hope to offer a permanent artificial hip - much more user-friendly than today's models that come unglued and require replacement after only 5-10 years of use. It's just one more way space research helps to make life better on Earth."

Comments

Yes But

[4of12]

I know they're trying to reduce the effect of buoyant (natural) convection by going into the microgravity environment. And, pure density-driven convection due to the differences in density of air and molten ceramic will also be minimized in space.

But if there are temperature gradients in the molten ceramic, they might still have to contend with molten bubbles migrating due to thermocapillary (Marangoni) convection. The surface tension of the air/liquid interface is generally a function of temperature.

Good luck to them, anyway.

AVN a reason to keep looking for better prostheses

[paulsc]

Bo Jackson, and many other middle aged people, including myself, lose their hip joints to AVN (avascular necrosis) or accident. At 42, I had crippling pain in both legs, so intense that a ten step walk down the hall to the bathroom was eventually an impossible journey.

AVN is a result of the human body's Architect and Prime Contractor making the entire blood supply for the head of the femur a single, badly oriented blood vessel. If the vessel becomes blocked or narrowed, the top of the femur loses its circulation and dies, and the cartilage necessary to keep the natural joint working can't be repaired. Within a short time, dead bone is grinding against living cartilage in the pelvic socket, which wears out quickly and painfully, or the head of the femur breaks, and dead, can't heal. This happens every year to a single digit percentage of the population, about evenly distributed between men and women. Smoking and some other personal health issues, including race and heredity, have been statistically linked to AVN, but no studies of which I'm aware have firmly established a causal relationship between health behaviors, environtmental factors, heredity and AVN. Accidental breakage is a another reason hip replacement surgery is performed, especially if the femoral head is severly damaged, and is unlikely to be able to heal.

100 years ago, and even today in medically underserved areas, hip joint failures, and the resulting loss of locomotion, resultant infections, and stress cause(d) high rates of subsequent mortality, within a few months, as other posters have mentioned. The various forms of hip prostheses are thus literally life saving devices, not just ways for little old ladies to enjoy a few more Arthur Murray dance lessons. It is hard for healthy people to appreciate just how debilitating and life threatening the loss of mobility is, but I assure you, it is a very, very real threat to life, within weeks, from many mortality paths.

The literature quotes the common "life span" of THR (total hip replacement) type prostheses at an average of 10 to 12 years. I have one that was originally installed in 1994, and the other which was a revision done in 1999, due to involvement in a tripping type accident. The joint replaced in 1994 appears sound in follow up X-rays, which look to predict failure by picking up very small particles in the extra cellular fluid, or in the joint parts themselves, near the joint movement surfaces, indicating that significant spalling wear is present. But the far more usual cause of failure is actually failure of the cement or bone that hold the joint parts in place. The usual indication of such failure is pain, caused by small fractures and infection of the bone surrounding the implants, or excessive movement of the implant parts in the bone cavities of the pelvis and femur made during surgery. In my case, and that of thousands of other THR patients of recent years, the former practice of cementing the replacement parts to living bone has changed to having the surfaces of the parts present a rough surface, to which living bone, which is accurately "machined" during surgery using jigs and a reaming toolset provided by the joint manufacturer, to achieve very close tolerance fit of the artifical hip parts to the living bone remaining. Under such close tolerances, and with immediate physical therapy, new bone will actually grow into the the implant surfaces, and be superior in overall life to the cemented versions. This remains an on-going investigation where ceramic surfaces show real promise.

Many designs of hip prostheses are easily damaged by torque moments and shock loads presented to the joint during common situations such as minor stumbles, or kicking or pushing small but dense objects. Learning to respect the hardware, and being very careful about shoes, walking surfaces, and instantaneous loads is all part of having the mobility the artifical joints provide. With care, most activities can be managed, and don't "wear out" the joints, but activities that put deformative shock loads into the plastic or metal "cup" parts surrounding the "ball" surface of the femur replacement portion of a THR are really, really bad ideas, and can result in premature or even instaneouses failures. This is more often due to crush and fracture failures of the supporting bone tissues, but in my case, I actually sheared a 3/8 inch diameter stainless steel "rod" forming the offset for the "head" of the femoral replacement part. There may have been some prior contributing damage to the joint part from surgical insertion damage, or in vitro degradation, but it is hard to know since the removed parts are hard to analyse, may suffer additional damage in extraction, and are often changed by years of immersion in the fluids of the living body.

If I live to a normal age for a man of my background, I'll face the surgeon another 4 to 6 times for revisions, so I'd like to see a "permanent" THR developed, as would thousands of others. Advanced materials leading to a substantially stronger, longer lived joint, are the most desirable course, and probably, the most likely. I applaud the folks involved in this, and I am grateful to the American taxpayers, and to NASA for time and space aboard shuttle missions, to do the early science that might lead to such materials.