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Kevin Stone, M.D.: Strides in Cartilage Growth and Repair


May 08, 2001

Dr. Kevin Stone is an orthopedic surgeon specializing in sports injuries, particularly those of the knee and shoulder. He is recognized internationally as an authority on cartilage growth, replacement, and repair. He is a founder and chairman of the Stone Foundation for Sports Medicine and Arthritis Research, a leading center for treatment of athletes with joint injuries.


Since 1988, Dr. Stone has been a physician for the U.S. Ski Team and the World Professional Ski Tour. He has also been the physician for the U.S. Olympic Training Center, The U.S. Olympic Festival, the International Winter Special Olympics, the Smuin Ballet and other numerous sports and dance organizations.


Dr. Stone received a B.A. from Harvard College and an M.D. from the University of North Carolina School of Medicine. He completed his internship in internal medicine at Harvard Beth Israel Hospital, a residency year at Stanford University Hospital and orthopedic residency at the combined Orthopedic Residency Program at Harvard.




Knee1: What first attracted you to working with the knee?


I injured my own knee playing soccer at Harvard, and the orthopedist who repaired my knee impressed me. I realized that I was interested in solving the problems of athletes and people with arthritis.


Knee1: What’s the greatest challenge in your opinion, to working with the knee?


It is a beautifully designed joint that goes through one to three million cycles, or steps per year, and carries up to five times its body weight. Nature has designed a joint that man cannot reproduce, yet at the same time it does respond to efforts to stimulate healing and to re-grow cartilage. The more we learn about it, the better we are at restoring the knee to its original function.


Knee1: You concentrated some of your efforts towards cartilage regeneration. Can you explain some of the work that you have done in this area?


Starting in 1984, I began a project to figure out how to replace the meniscus cartilage. In the first ten years of my research, I focused primarily on re-growing the meniscus cartilage, and did that by designing a collagen scaffold, which was designed to act as a regeneration template to re-grow the meniscus. We eventually received FDA-approval to implant that design in humans, which we started doing in 1990 at The Stone Clinic in San Francisco. The scaffold is now available in Europe and in Australia, and is completing a wide clinical trial in the United States. We will use it for people who have lost a portion of their meniscus cartilage, rather than all of it. We will use it to re-grow that segment of missing cartilage.


What areas of the meniscus does this procedure repair?


It primarily repairs tissue in the posterior and the mid-section of the meniscus cartilage. We have learned that we can take even a vascular regions, which are regions that do not receive blood and make them vascular by creating a new blood supply in the area.


How do you do that?


We do that by needling the periphery of the meniscus, so we can stimulate a new blood supply to the central portion.


How have advances in the last few years of technology eased your work with cartilage and meniscus repair?


In the progression of re-growing meniscus, we shifted in 1993 or 1994 to replacing the entire meniscus cartilage. We did that by improving the techniques of meniscus allograft replacement, where we take a meniscus from a cadaver and use that to implant it in a human’s knee. A friend of mine in Germany started that procedure in 1986, however the replacement technique was slow to evolve into a successful technique. I wrote the first technique paper in 1991. After time we started to improve the technique; now we are able to replace the meniscus cartilage in young people as well as in older people who might want to delay the time in which they need total knee replacement. In our most recent studies at The Stone Clinic, we transplanted meniscus cartilage in fifty people with arthritic knees and so far have been able to delay the time in which they would go on to a total knee replacement.


What was your success rate with that?


So far, in the last four years of about fifty meniscus replacements in arthritic knees, only three of those arthritic patients have gone on to a unicondylar or a total knee replacement—and these are severely arthritic knees. However there is a 14% re-tear rate of the allograft in arthritic knees in this time period.


Starting in 1996 we started a project to see if we could use pig tissues to replace the cartilage inside the knee. Our focus there is to see if we can remove the antigens, or the carbohydrates that cause tissue rejection from pig tissue, so they could be used to replace human tissues. That project has now moved far enough along that we expect to start replacing tornanterior cruciate ligaments (ACLs) in humans with pig ligaments this coming summer. The product is called Z-Lig and is produced by a company we formed called CrossCart Inc. in San Francisco.


With whom have you worked on the project—the University or a research laboratory?


We started that project and funded it independently. We formed a private company, CrossCart Inc, which built its own laboratory here in San Francisco. The first product that will come out of that research will be a new ACL, or anterior cruciate ligament. Currently people who rupture the ACL today have their own patellar tendon, hamstring, or occasionally a cadaver allograft used to re-build their ligament. It is our expectation that if the pig tissue transplant is successful, people will no longer have to harvest their own tissues in order to rebuild the knee.


How is the pig tissue graft harvested?


After the pig is used for meat, the heart valve is sent off the folks who use pig heart vales. We then obtain the knees, and harvest the patellar tendon with bone just as we would from human. We take that out and use enzymatic techniques to remove the antigens. Then, we sterilize the tissue. The pig bone-patellar tendon-bone is the graft that would be used to rebuild someone’s ACL. The beauty of it is that the tissue is as strong as that of an eighteen year old. So even if you are forty or fifty and you have ruptured your cruciate ligament, rather than using your own tissue, you would be able to get strong young healthy and sterile tissue. Additionally, if we were to hand this graft to an orthopedic surgeon and not tell him if it was a human’s tissue or a pig’s tissue he wouldn’t be able to tell the difference—the tissue is very similar.


Is it the same length as a human ACL?


Yes, we can vary the length, depending on the size of the pig.


How have the advances in technology helped your research and you practice?


For us, advances in technology have been helpful both on the tissue treatment side and the implantation side. We’ve been able to harness some of these biochemical treatments in treating pig tissues, in order to make them transplantable, in order to make better scaffolds, which is what we used when we designed the meniscus scaffold. We’ve also used advances in instrumentation in order to make the surgery that we use for people’s knees less painful, through smaller holes, and done virtually completely as an outpatient.


What have been some of the greatest advances in arthroscopy in the last few years that you’ve used to repair knees?


Most recently, the advances in instrumentation have permitted us to harvest articular cartilage and bones from people’s knees and make a paste out of that tissue. We use that paste, which is called paste grafting, in order to repair arthritic defects of traumatic defects in articular cartilage. The instrumentation advances have permitted us to develop new techniques to regrow damaged areas of cartilage. That is the first one that has influenced our practice. The second one is that we have been able to work on a new osteotomy technique where we’ve been able to correct misaligned knees, which is bow legs, through much smaller incisions, and using wedges in order to open the bone rather than plates and screws as we used to have to do in the past.


You were also one of the first to remark that it was unwise to let a PCL tear go untreated. Can you explain what the role of the PCL is and the long-term effect of injuring that ligament?


The posterior cruciate ligament is the central pivot point for the knee joint. When you injure the PCL, most commonly from banging your knee on the dashboard when you car hits an immovable object or when skiing or snowboarding and hitting a tree, the tibia is driven posterior and the femur is driven anterior and the PCL will rupture. When it ruptures, you lose that central guide wire of the knee. We know that although many people can function adequately with out it, over time they tend to wear out the medial compartment of the knee, the inside portion of the knee, and they develop arthritis in that area, because the joint mechanics have become abnormal. Surgeons have been reluctant to rebuild the PCL in the past because the surgical techniques only used to lead to fair results and the rehabilitation post-operatively was thought to require a long period of immobilization. What we found more recently is that the PCL can be reconstructed by principles similar to the ACL, in that early mobilization or early strength training after reconstruction leads to better results than we had though in the past. Those results tend to protect the knee better than leaving the PCL untreated.


How do you repair the PCL?


Surgically at the time of rupture, if we see it freshly ruptured, we can insert sutures by a arthroscopic technique and anchor that PCL back to the bone, all arthroscopically. If the PCL is completely ruptured in its mid-substance, then it is better to go ahead and reconstruct it primarily. We most commonly do that by using the patellar tendon bone construct that we use for the ACL. We hope in the near future that we’ll be shifting to pig tissues as well.


Can explain how nutrition plays a role in orthopedic injuries?


I think we’ve learned a lot form our patients over the last few years. Probably the most important thing is that there are things people can eat or take that influence their joint health. The most important one has been glucosamine. Our patients came into our office saying, I have taken this supplement glucosamine and have given up taking my ibuprofen. We like most physicians, didn’t listen as carefully as maybe we should have the first couple of years, and after awhile so many of our patients were reporting relief that we started reviewing the available literature. We found that glucosamine, taken orally, is absorbed into the cartilage, and tends to hydrate the cartilage, which is way we think people’s knees tend to feel so much better when they take glucosamine. We have become convinced enough that we’ve actually developed a beverage for our patients because they hated taking the large glucosamine pills. We called it Joint Juice, and it’s provided some fun for us and the ability to help our patients take a nutrient that we think is really helpful for their joints.


How do patients get their hands on joint juice?


They can find it at JointJuice.Com as well as Alberston’s and Raley’s stores in Northern California.


There have been few if any United States studies on glucosamine, but you would still recommend it for your patients?


We have an enormous amount of anecdotal results from our patients, for one. For another, we did review the world’s literature on prospective double blind studies that were done and concluded that enough of them were suggestive of beneficial effect, as did the Journal of the American Medical Association. Lastly, we will be initiating a study where we will shortly be feeding Joint Juice to rabbits whose ACLs have been cut. We know that in a rabbit, by three to six months when you cut their ACL, you create an arthritic knee. Additionally, in those rabbits, we are going to create articular cartilage legions. W should this year be able to answer the question when an animal is fed Joint Juice glucosamine does it have a beneficial effect on repairing cartilage injuries or preventing arthritics. I think that study will be very helpful in answering those questions. Lastly, there is a national NIH funded study right now of people taking glucosamine to determine its effectiveness.


With advances in procedure and technology that you have described, do you see us winning the war against arthritis in the next few decades?


Yes, I think we are making huge strides, both on a hormonal/genetic/chemical level as well as on the treatment of the disease itself.


Do you have any tips on what people can do to keep their knees healthy this spring as they return to physical activity?


We ask our patients or athletes to do something athletic every day, as opposed to two or three times a week. Do something you enjoy from a training or activity perspective for a minimum of twenty minutes a day. This activity must boost the heart rate to be effective. For those who are dedicated to one sport or one activity, we have focused quite a bit on cross training—varying the activity. A cyclist can mix up their bike training with weight lifting or pool exercises. We find variety keeps athletes interested, helps train their bodies, and helps prevent injuries.

Last updated: 08-May-01

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