Ways to Heal Broken Bones : Part 2

by Food and Drug Administration (FDA)

(Page 2 of 3)

Approved replacements for fractures in shoulder joints also consist of a ball and stem.

Andrew Bender, M.D., the orthopedist who implanted Wallace's partial replacement, says this simple model has been in use 30 to 40 years. "It has different size balls, one size stem, so it's not an exact fit. But it gives what we call a three-point fixation for some immediate tightness. The stem has holes for bone to grow through and across for more permanence."

Bender pressed in Wallace's device without cement, a snug fit. He cements only if the fit is very, very loose. "Modern day hip replacement without cement is relatively quick, both sides. She had only one side done and good bone, so it didn't take long."

If a replacement fails, it usually does so within 5 to 10 years. Simple models tend not to fail in the very old, Yahiro says. "A person in a chair or bed most of the time won't put demands on the joint that, say, Bo Jackson does." (Jackson had a hip replacement in 1992 due to a football injury.)

For higher demand, there are more precisely fitted models.

A robot that drills a more precise hole for the stem, to possibly keep the joint intact longer, is under investigation for use in cementless hip joint replacements. (See "Robots in the Operating Room," July-August 1993 FDA Consumer.)

An external fixator — a pin-and-rod frame — can keep the joint from being compressed by other bones, to heal before a load, or stress, is put on it again. Pins are inserted on one side of the limb through the skin, muscle and bone, out the other side, and attached to the external rod, forming the frame.

About 30 percent of patients get infected at the pin site, so meticulous hygiene is crucial. "It's a race," says Kenneth McDermott, who reviews the devices for the Center for Devices and Radiological Health. "The pin goes through the skin, and infection can go right down the pin."

Internal fixation devices pose less risk of infection. These metal plates, rods, wires, screws, nails, pins, staples, and anchors may sometimes be left in. A tiny pin may not be felt, but plates or screws may cause irritation or pain. The decision whether to remove the device in a second surgery is made on a case-by-case basis.

Surgery to remove a screw in the very old may be too risky. For a 20-year-old, benefits of a second surgery may outweigh risks. In the ankle, plates and screws are customarily removed. Yahiro says, "The bones are so superficial, the device often rubs on the shoe."

McDermott gives another reason for removing a plate or screw: "It can take the load off the bone, causing the bone to resorb and weaken."

Fixators and internal fixation devices are used also for some mid-bone fractures.

Grafts

The surgeon may graft bone to replace a missing segment that had to be surgically removed due to infection.

For a small segment, tissue can be taken from the patient's own bone (autologous graft).

Cadaver bone (allograft) may be used, especially for a large segment. Though dead tissue, cadaver bone provides a scaffold for living bone to grow into and remodel the graft. For healing to occur — and sometimes it doesn't — the body must put blood vessels into the graft to nurture the new living bone as it replaces the dead tissue. Healing takes longer than with an autologous graft.

Another option is a substitute bone graft, fashioned with help from nonhuman substances. FDA recently approved two such grafts:

Pro Osteon Implant 500 Coralline Hydroxyapatite Bone Void Filler(1992) — Fills holes near the ends of long bones in adults. It derives from marine coral, whose spongy calcium structure resembles human cancellous bone.

Collagraft Bone Graft Matrix(1993) — Treats long-bone fractures and other injury-caused areas of missing bone of 30 milliliters (1.8 cubic inches) or less. The product — consisting of purified cow collagen and a chemical, hydroxyapatite-tricalcium phosphate — is mixed with the patient's marrow into a paste and put into the area of missing bone to encourage new bone growth. It's not for use in certain patients, such as those with osteomyelitis (bone inflammation) at the fracture site, severe allergies, or allergy to cow collagen, and those being desensitized to meat products, as the treatment injections may contain cow collagen.

When these substitute grafts are placed next to healthy bone, the body remodels them in the same way it remodels human grafts. But according to Center for Devices and Radiological Health reviewer Nadine Rosile, "The substitute grafts aren't strong enough for use without a fixation device to stabilize the fracture."

A bone filler paste now under investigation, however, is as strong as bone within 12 hours, according to a report of a study of patients whose wrist fractures were injected with the paste. The report, in the March 24, 1995, issue of Science, stated that the paste stabilized the bone during healing and was eventually remodeled. The patients had greater grip strength at six months than historical controls (other patients in the past who had not been treated with the paste) had at two years, the report stated.

Also under investigation are injections of growth factor proteins, such as morphogenic protein and transforming growth factor-beta, found naturally in the body in very small amounts.

"The proteins turn on cells to produce bone," Yahiro says. "Animal studies show growth with injections similar to that with autologous grafts." The hope, he says, is that injected fractures, even with large areas of missing bone, will heal faster and be stronger, without grafts.

About the Author

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