CELOS RESEARCHERS
PUT THE RIGHT FOOT FORWARD

Steven Infanti

Foot complications are one of the long-term consequences of diabetes, and it is not surprising that diabetes is the leading cause of nontraumatic lower-extremity amputations in the U.S. There are more than 60,000 lower limb amputations a year in the United States among people with diabetes, but researchers in the college believe that improved techniques for foot care and healthcare provider education can reduce those rates.

While people with diabetes may check their glucose levels frequently, many of these patients and even members of the health community fail to monitor the condition of their feet. The college's Center for Locomotion Studies (CELOS) hopes to change the way the medical community and people with diabetes think about foot complications, and to reduce the number of lower limb amputations among this group.

"Amputations can be prevented and reduced among people with diabetes," says Dr. Peter Cavanagh, director of CELOS. Cavanagh and other CELOS researchers have been compiling data for years that allows them to identify high-risk patients before they develop foot lesions. Physicians and patients once thought vascular disease, or poor circulation, was the major factor in diabetic foot problems. While vascular disease can play a role, it is now recognized to be a secondary issue in most cases, says Cavanagh.

After 10 to 15 years of living with the disease, people with diabetes have a 30 to 50 percent chance of experiencing damage to the nerves of their feet and legs. This damage affects all part of the nervous system, but it is the loss of sensation that can cause most problems for the feet, says Cavanagh.

"The loss can be so severe that people can injure their feet without realizing it," says Cavanagh. A simple abrasion on a diabetic's foot can go unnoticed and untreated. It's possible for a person with diabetes to get an ulcer on the plantar surface of the forefoot, for example, which can becomes a ready portal for infection. If the ulcer goes to the bone and an infection starts, the only treatment for infected bone is surgical removal.

"The most common type of injury is skin breakdown due to repetitive stress - walking in poorly cushioned shoes that allow stress to be applied to a prominent bony region of the foot," says Cavanagh. The research at CELOS is based on the belief that foot injury, such as an ulcer on the bottom of the foot, results from a mechanical insult to insensitive tissue. Thus an injury has to be healed by removal of mechanical stress, and the healed foot has to be kept from future damage by providing an acceptable mechanical interface between the foot and the world for the rest of the patient's life.

Research at CELOS on healing has shed light on the mechanism of action of a frequently used treatment called the Total Contact Cast (TCC). In this approach, the foot is encased in a close fitting plaster cast that specifically isolates the area of the ulcer from stress. Although the treatment needs specialized care and frequent cast changes, it has been shown that application of a TCC can heal ulcers that have existed for many months or years in a typical time of 6-8 weeks.

"While previous conventional wisdom had suggested that the cast distributes pressure evenly over the entire surface of the foot, our research shows that this was not the case, and that local pressure reduction in the area of the ulcer was the key," explains Cavanagh.

The Total Contact Cast is one of the many approaches used in the Penn State Diabetic Foot Clinics at the University Park campus and the Hershey Medical Center, which were founded by Cavanagh and Drs. Jan Ulbrecht and Greg Caputo. These clinics, which have served thousands of patients, are collaborative ventures between the Departments of Medicine and Orthopedics and Rehabilitation at the Hershey Medical Center and the College of Health and Human Development.

The research work at CELOS is both experimental and theoretical. Typical of the experimental approach is a recent study, Cavanagh notes, which examined the optimal design for a type of footwear called a rocker shoe.

This shoe features a rigid contoured outsole which allows the patient to walk without extending the metatarsophalangeal joints of the foot. The skin overlying these small joints between the toes and the ball of the foot are key sites of plantar ulceration, and research has shown that extension of the joints causes the natural protective padding to be moved away from the bony prominences.

By using pressure sensitive insoles between the shoe and the foot while varying the geometry of the outsole, CELOS researchers showed that pressures on the ball of the foot could be relieved by as much as 40 percent. An ongoing investigation of the tissues in this region of the foot is being pursued using high-resolution Magnetic Resonance Imaging (MRI) in collaboration with the faculty from the Department of Radiology at The Milton S. Hershey Medical Center.

The complexity of foot structure and of the interaction between the foot and the shoe has led researchers to develop mathematical and mechanical models to predict the best methods of relieving injury-causing stress. One such approach, an engineering technique called finite element analysis, involves representing the complex structure of the foot as thousands of small geometric elements with well-defined properties. Dr. David Lemmon, a CELOS engineer, has shown that such models can be predictive of experimental data with a remarkable degree of accuracy. This approach offers the researcher the opportunity to test many different combinations of foot-shoe interfaces to identify the optimal condition for a given foot. An undergraduate honors student from the College of Engineering, Jeff Saucerman, is working at CELOS to extend the complexity of the current models for his honors thesis.

A unique cadaver model has been used by CELOS faculty member Dr. Neil Sharkey, to investigate the role of Achilles tendon lengthening, a procedure often used by orthopaedic surgeons on diabetic patients to reduce pressure under the ball of the foot. Sharkey and his students have built a simulator which moves a foot through a typical pattern of motion while applying typical muscle forces to the tendons which cross the ankle.

This results in a simulation, which is remarkably similar to the mechanical conditions which occur during normal walking. Application of this approach has shown that Achilles tendon lengthening is an appropriate procedure for patients with severely restricted motion at the ankle.