They are the generation that popularized jogging, marathon running, racquetball and mountain biking. And now, more of the 78 million baby boomers born between 1946 and 1964 are wearing out their bodies at an earlier age than their parents or grandparents.

They are the generation that popularized jogging, marathon running, racquetball and mountain biking. And now, more of the 78 million baby boomers born between 1946 and 1964 are wearing out their bodies at an earlier age than their parents or grandparents.

Doctors are regularly seeing them for worn-out knees, hips, shoulders and spinal discs. They have arthritis, tendinitis, bursitis and stress fractures. They struggle with the national predisposition toward weight gain even as their doctors advise them that regular exercise prevents everything from diabetes to Alzheimer's disease.

Not surprisingly, the generation of improvisation, ingenuity and innovation is counting on technology to keep its members active into old age.

There are some medical technologies available to help them, and others are on the horizon, says Dr. Sean Hassinger, an orthopedic surgeon at Presbyterian Medical Group.

Success of the procedures and devices, however, often is a function of realistic expectations on the part of the patients, he says. Many times, a person's level of activity has to change after surgery.

"Knees are the most commonly performed procedure and site of problems," Hassinger notes.

About 534,000 total knee replacements and 235,000 total hip replacements are done in the United States each year, and the numbers are increasing annually, according to the American Academy of Orthopedic Surgeons.

The prosthetics being used today are far superior to the earlier versions, and the latest generation of replacements boasts of "highly cross-linked polyethylene plastics that show little to no wear in patients who have had the implants for a number of years," Hassinger says.

A smaller group of patients may be candidates for partial knee or partial hip replacements, in which an implant is used only on the portion of the joint that is arthritic. That allows for less trauma to the joint, preservation of more bone, a smaller incision and faster post-surgery recovery.

Joint resurfacing, or arthrosurfacing, is another option being used by some doctors in hips, says Hassinger.

The hip socket is sometimes replaced as in a traditional replacement surgery, but rather than replacing the ball at the top of the femur with an artificial ball attached to a metallic stem, the existing ball is retained and reshaped to hold a metallic cap. "The concept is similar to capping a tooth," Hassinger says.

Depending on the type of replacement required, a minimally invasive surgical technique may be used.

"The goal should be elimination or mitigation of pain and a return to a more active lifestyle," Hassinger says. But implants don't provide the same range of motion as a healthy knee or hip.

Walking, swimming, using elliptical or treadmill machines are fine; running, jumping, cutting or torquing motions should be avoided. Consequently, people with replacements should stay away from high-impact sports or exercises such as basketball, baseball, football, soccer, jogging, sparring and the like.

High-impact activities can cause wear on an implant and even cause it to become loose, he says.

Elbow replacements use the same materials as hip and knee replacements.

The diseased joint surfaces are cut away and metal stems are pressed into the humerus and ulna, the two bones on either side of the elbow joint. The two stems are then joined by a hinge or a polyethylene ring, depending on the design.

The replacements have a higher failure rate and are best used on people with low physical demand on the joint.

Better for active boomers is a procedure called fascial interposition in which damaged articular cartilage and bone spurs are removed from the damaged joint. The surgeon then harvests, locally or from another site on the body, a flat piece of fascia tissue, the connective tissue that wraps around muscles. The tissue is folded and fastened into the elbow joint to act as a cushion.

The tissue isn't as tough as cartilage but should function well for 10 to 15 years or more. People who have had the procedure should avoid torquing motions of the arm as well as heavy weight lifting or activities that involve hard throwing, Hassinger says.

Total shoulder joint replacement surgery alleviates pain by replacing the damaged bone and cartilage with a metal and plastic implant.

"You won't get normal range of motion and most people shouldn't expect more than 150 degrees of flexion," Hassinger says.

Implants are also available to replace the large knuckles that join the hand bones to the finger bones, as well as implants to replace the smaller joints of the fingers.

Pain relief is excellent, range of motion is good but not normal.

The most common site for arthritis in the toes is the large joint at the base of the big toe, although arthritis can certainly cause problems at the other toe joints, too, says Dr. Richmond Kilpatrick, a podiatrist with Presbyterian Medical Group.

Total and partial joint replacements are available for the toes.

Another alternative is arthosurfacing, Kilpatrick says, in which damaged cartilage is removed from an arthritic toe joint and a metal cap is attached to one of the bones. The capped surface simply articulates against the end of the other bone.

One of the best methods of pain relief remains fusion, in which the surgeon removes part of the toe joint, letting the toe bones grow together, or fuse.