Clinical trial aims to improve knee injury treatmentWEST LAFAYETTE, Ind. -- While football players toss the pigskin on the field, physicians are using another part of the pig to tackle a common but serious knee injury associated with sports.
Clinical trials are under way to test a new material derived from pigs' intestines that, when inserted into the human body, may serve as a scaffold around which the body can regenerate damaged tissues, such as torn ligaments or tendons.
The new material -- which is, in essence, sausage casing -- was developed through a partnership between Purdue University and DePuy Orthopaedics Inc. of Warsaw, Ind.
Stephen Peoples, vice president of clinical and regulatory affairs at DePuy, says the company has received approval from the FDA to initiate Phase I clinical trials of a device made from the material. It will be used to replace ruptured ligaments in "blowouts," or anterior cruciate ligament knee injuries, that involve damage to a ligament that runs from the femur, or thigh bone, to the tibia, the bone below the knee.
Such knee injuries are common in skiers and also occur in sports such as soccer, basketball, volleyball and football. The injury occurs when a player suddenly decelerates or quickly stops, changing direction at the same time, causing an overextension of the knee joint in either direction.
The new material offers hopes of a less invasive treatment and a more comfortable recovery for patients with such knee injuries, says Dr. Stephen F. Badylak, director of research for Purdue's Hillenbrand Biomedical Engineering Center and head physician for Purdue's athletes.
The Phase I clinical trials will begin this month. The first 12 surgeries will be carried out at Valley Presbyterian Hospital in Van Nuys, Calif., and at Aspen Valley Hospital in Aspen, Colo.
The material, called SIS for small-intestinal submucosa, is derived from the middle layers of the small intestine of pigs. Once these layers of intestine are removed, they are disinfected and processed into different forms, such as tubes, sheets or fibers, and sterilized and stored for future use.
Though the intestinal lining that gives rise to the raw material for SIS is very thin -- 80 to 100 microns, or about as thick as a piece of office paper -- the material is extremely strong, Badylak says.
Animal studies show that once the material is placed within a body, it appears to aid the body's natural healing response.
"For example, when SIS is inserted into the site of a wound, there is a proliferation of new blood vessels created in the immediate area," Badylak says. "This is very important in the wound-healing response, because the blood vessels not only nourish the graft, but they also bring to it all the molecules the body needs to rebuild the tissue."
This ability to remodel makes SIS ideal in orthopedic applications such as replacement material for damaged ligaments and tendons, Badylak says. Torn or damaged ligaments and tendons -- the fibrous tissues that connect bone, cartilage and muscle -- make up the bulk of sports-related injuries.
"Anterior cruciate ligament knee injuries can be a career-ending injury for many athletes," he says. "The surgical procedure used to treat this problem usually involves taking a piece of connective tissue, or tendon, along with some bone from a separate location in the same knee and replacing the injured ligament. This procedure can be as traumatic to the patient as the ligament tear."
Other treatments that have been used for this type of knee injury include replacing damaged ligaments with synthetic fibers. Badylak says synthetic implants tended to fail or weaken over time.
Animal studies with SIS have shown encouraging results. When damaged ligaments are removed and replaced with long, thin strands of SIS material bundled together, the replacements form a new ligament-like structure of collagen infiltrated with cells, and become stronger over time. The SIS material is anchored to the bones through small holes drilled for this purpose.
"The SIS implants generally start out weaker than synthetic ligaments, but become heavier and stronger with use, just like natural tissue," Badylak says.
Though SIS comes from a biological source, the studies to date indicate there are no problems with rejection. Badylak says he believes that the material is readily accepted because it is composed of molecules that are very similar to human molecules and it works alongside the body's own repair mechanisms.
"We're using a mixture of molecules developed and organized by Mother Nature," he says. "SIS is a composite of connective tissues that include collagen, proteins, growth factors and various other molecules."
Badylak says this natural mix of proteins and other molecules may help induce the body to "rebuild" injured tissue by providing a framework for cells on which they can build new tissue.
"Animal studies show, for example, that when SIS is inserted into a body, neighboring cells migrate to the area, which then allows the body to rebuild and perform like the original tissue," he says. "We suspect that once the body deposits its own proteins and molecules at the site, the SIS is degraded and eliminated from the body."
Dick Tarr, vice president for research and development at DePuy., says, "We are extremely excited about this breakthrough technology and our success in moving from the laboratory to human trials."
The Purdue-DePuy team also plans to expand applications for SIS into other orthopedic areas such as tendons and other musculoskeletal tissue applications. DePuy has obtained exclusive rights to orthopedic applications of the material.
The Purdue group also is working with a number of other companies and institutions to develop additional applications in other body systems such as the skin, urinary bladder and the heart.
DePuy is the world's oldest orthopedic company and is a leading designer, manufacturer and distributor of orthopedic devices and supplies. Its products are used primarily by orthopedic medical specialists and, in the case of the company's spinal implants, spinal specialists and neurosurgeons. Its products are used in both surgical and nonsurgical therapies to treat patients with musculoskeletal conditions resulting from degenerative diseases, deformities, trauma and sports-related injuries.
Sources: Stephen F. Badylak, (765) 494-2995; e-mail, firstname.lastname@example.org