MENISCUS MIRACLE "The implant restores a lot of the function that native cartilage provides," says Christopher Kaeding, MD.

Once the knee's cartilage goes, it doesn't come back. The limited healing potential and limited options for repair of this shock absorber between femur and tibia have traditionally spelled a steady progression of pain, osteoarthritis and ultimately joint replacement. On the horizons of sports medicine, however, orthopedic surgeons are eagerly observing whether emerging developments might slow the damage, restore function and even regenerate cartilage. Are these advancements the future of knee repair?

Meniscus implants
Christopher Kaeding, MD, first heard about the possibilities of a plastic meniscus implant during a peer's presentation at the American Academy of Orthopaedic Surgeons conference a few years ago. "He said he was working with a group that was developing an implant that could offer some advantages, and asked 'Are you interested in working with us?'" he recalls.

Since the conventional treatment of damaged or deteriorating cartilage tended to involve either routinely icing of the knee (inexpensive and accessible, but not a long-term fix) or undergoing partial or total knee replacement surgery (as solutions go, a last resort), his answer was an enthusiastic yes.

After reviewing the group's preliminary studies and visiting their lab for a training session on the implant's sizing and insertion, Dr. Kaeding, the executive director of sports medicine at Ohio State University's Wexner Medical Center in Columbus, Ohio, led the nation's first FDA-approved, multi-center, randomized control trial for the NUsurface Meniscus Implant, manufactured by Active Implants.

"The implant restores a lot of the function that native cartilage provides," says Dr. Kaeding. "It makes the surface of the 2 bones, the femur and the tibia, more congruent. They match up better. When their contact area is larger, it spreads the load over a wider area, which dissipates the peak contact forces."

The clinicians' hope is that this supplemental implant will decrease the persistent pain of a damaged or decaying meniscus, slow the development of arthritis, and postpone or prevent the need for knee replacement surgery. Evidence-based findings are still years away, but based on the handful of trial surgeries Dr. Kaeding has undertaken at his site and the reports of the hundred or so done in Europe and Israel in recent years, the outlook looks outstanding.

PATCH WORKS The successful outcomes of autologous chondrocyte implantation have stoked the excitement surrounding stem-cell-driven cartilage repair.

"I've been impressed by how quickly patients are off crutches and back to normal activities," he says. "It's only taken them about 12 days to 2 weeks."

The insertion procedure is low-impact. A knee arthroscopy prepares the site — "we want to reduce the meniscus to a nice vertical rim," says Dr. Kaeding — and the plastic implant is slipped in through a small incision to supplement and replace the weakened or missing cartilage. "It appears that over time, it contours to a patient's natural anatomy, but that's not certain yet," he notes.

Another uncertainty is just how large of a patient population, and at what stages of injury, this implant might help. "We don't know how much arthritis you can have in the knee and, when you put an implant in, still get relief," he says. The FDA trial, due to its closely regulated nature, is unlikely to definitively answer the question of best candidates. "The inclusion and exclusion criteria of who's eligible is tight. The patient has to have lost meniscus on the medial side, and suffer pain, but their arthritis can't be too advanced."

The eventual comparison of outcomes between the trial subjects who receive implants and those who get injections, physical therapy and a knee brace should be enlightening, says Dr. Kaeding, and if the implant ultimately receives the FDA's pre-market approval, it'll open avenues for further exploration. "Hopefully, this is a solution," he says.

QUALITY CHECK A custom-made knee implant is inspected and compared to its manufacturing specifications.

Stem cell transplants
In another corner of sports medicine, physicians are exploring not just how to forestall the decay of knee cartilage, but also whether this damage could possibly be reversed. The main ingredient in this repair would come from within the patient's own body, with an assist from science.

The growing excitement surrounding stem cell therapy comes from its versatility, says Christopher C. Dodson, MD, an attending orthopedic surgeon at the Rothman Institute in Philadelphia, Pa., and an associate professor at Thomas Jefferson University. Derived from the bone marrow from a patient's hip or adipose tissue from their abdomen or buttocks, "stem cells can become anything in the right environment. They can grow cartilage, and they can heal lesions, with the same strength" as the original tissue, he says. "They can do tendon-to-bone or bone-to-bone."

Implanting stem cells into a compromised knee could halt the progression of damage and regenerate lost cartilage. It might even accelerate healing. "Where we think this will be especially beneficial is among young athletes," says Dr. Dodson. "ACL healing is always a challenge. While we're waiting for the healing, what if there's a way we could speed things up?"

Given the strong outcomes he and his colleagues have seen from autologous chondrocyte implantation (ACI) in sports injury cases, they're eager to put stem cells to the test. In ACI, small strips of cartilage are arthroscopically removed from the joint. In a laboratory environment, the chondrocytes — or cartilage cells — are isolated and cultivated for 6 weeks until they increase in number. Thus revivified, they're injected into the joint beneath a patch sewn in as a scaffold during open surgery. In the best-case scenario, they kick-start the growth of new cartilage and fill in the defect. Because stem cells, like chondrocytes, originate from the patient's own tissue, the risk of rejection is low. But the advantage of stem cell implantation over ACI is that it doesn't require an initial harvest from the damaged joint.

There's a catch, though. At present, stem cells can't be "supercharged" for most knee repairs the way that chondrocytes can. While stem cells can be harvested from the patient and then injected directly into the joint, the amount that are put to work varies from case to case, which may affect the results. "We could concentrate them if we manipulate them in the lab, which would grow and multiply the number of cells," says Dr. Dodson. "But in the U.S., stem cells currently cannot be used when they've been manipulated in any way. The FDA hasn't approved that as safe. If we're going to manipulate, it has to be in the context of a trial."

Animal studies are experimenting with different methods of delivering stem cells to the diseased joint. It's an important consideration, says Dr. Dodson. "A gel or a scaffold is needed to hold the cells in the right environment. You want to prevent them from growing too much, as that could result in cell growth incongruity. And you want something made from inert materials, that the body won't reject."

But the eventual findings of human clinical trials, now underway and growing in number, would be even more valuable in comparing the safety and effectiveness of stem cell therapy to ACI and other repair strategies. Randomized control trials of arthritis patients have difficulties of their own, however. "The hard part is, no one wants placebos," says Dr. Dodson.

Also, as with the meniscus implant, clinicians haven't yet been able to determine a dividing line between the ideal candidate to benefit from stem cell implantation and the patient for whom knee replacement is the most viable option.

"Anecdotally, it shows great promise," says Dr. Dodson. "Truthfully, we don't know yet." He recalls when, a few years ago, platelet-rich plasma therapy was the next big thing that was going to revolutionize sports medicine. "We still use it, but sometimes it works great, and sometimes it doesn't make a difference. Overall, we're still confused about the healing response in the body. But time will tell."

Custom 3D-printed replacements
Beyond a certain degree of damage or disease, the most effective option for restoring the knee's structure and function is joint replacement. While prosthetic implants are available in a range of standardized sizes, they're not likely to provide a perfect fit in every case. 3D-printing technology, however, is making the concept of custom-made knee implants, designed to fit each patient's individual anatomy, a reality.

These on-demand implants promise not only a faster recovery with less pain, but also better alignment and more stability for improved function over standard prosthetics, says Gary Levengood, MD, of Sports Medicine South in Lawrenceville, Ga. He's placed more than 200 of the custom-made knees into his patients.

"I hear people report that probably 60% of patients who get off-the-shelf implants do remarkably well," he says. "But what about the other 40%? With custom, it's more like 95% who do extremely well. Patients have told me that the custom-made knee feels more like a natural knee. Over time, they find they're not constantly saying, 'This is a replaced knee.'"

A UNIQUE KNEE "Patients have told me that the custom-made knee feels more like a natural knee," says Gary Levengood, MD.

For the past 4 years, Dr. Levengood has been obtaining customized joints from a Massachusetts-based firm called ConforMIS. He sends a CT scan of the knee, as well as imaging slices of the hip and ankle in order to map the center of alignment. Computerized printers that are able to create solid objects layer by layer use the CT imaging data to form a wax mold of the knee joint, with which the company casts metal implants precisely the shape and size of the patient's own anatomy. Along with the implants, the company sends sterile, single-use, calibrated instrumentation designed and 3D-printed specifically for use in each case.

In the curvature of its condyles, the knee is more anatomically complex than the ball-and-socket hip joint. But recreating that unique radius of motion is not the only benefit that individualized implants offer, says Dr. Levengood.

An implant whose design is based on a patient's own anatomy means surgeons and their patients won't have to settle for one that's over- or under-sized. This in turn can reduce the procedure's lasting impact, since a surgeon may not have to remove as much bone to accommodate the implant. "It's really more of a resurfacing than a replacement," he says.

Additionally, conventional knee replacement surgery requires intensive soft tissue maintenance in order to rebalance ligament tension. Since customized implants are pre-balanced, that effort isn't necessary.

Implanting customized knees is accessible to any ortho doc who's performing the traditional procedure, says Dr. Levengood. With the help of regional anesthesia, an effective pain management plan, and a home-based physical therapy regimen, they can even be done outpatient. Dr. Levengood's patients can walk the hospital corridors shortly after their surgeries. As an added bonus, the delivery of customized implants and instruments means there's no expensive inventory to consign and store.

The ideal candidates for custom-made knees, he says, are healthy patients in their late 50s or early 60s who are active and want to remain active, but "it works across the spectrum, as young as 45, as old as 90. It's best with patients who don't have a lot of deformity in the joint."

There's no reason, he says, why the specialty knees can't run as long as traditional implant options do. "We don't have 20-year data, but the materials are the same as off-the-shelf models," he says. "Nothing in the metallurgy, nothing in the polyethylene, nothing in the cement is different. The difference is more about the shape than the composition, and the difference in shape means a difference in wear. You get less wear with a more congruent shape."

The application of custom-created implant technology isn't limited to knees, either. "I see custom joints of all types printed," he says. "Shoulders, hips, ankles, even wrists, elbows, fingers, toes. Any place you can do 3D mapping, you can create a custom joint." OSM