Exploring Innovative Treatment Options for Degenerative Disk Disease

Originally Published MDDI August 2001

R&D Digest

A monthly review of new technologies and medical device innovations

THIS MONTH: Exploring Innovative Treatment Options for Degenerative Disk Disease | New Analytical Technique Could Provide Tools for Assessing Parkinson's Disease Patients

New Implants Offer Relief of Spinal Pain

In April, the BAK/C Cervical Interbody Fusion System from Sulzer Spine-Tech (Minneapolis) became the first cervical interbody fusion device to receive marketing approval from FDA. The company previously introduced the first lumbar interbody fusion device, according to Sulzer Spine-Tech.

The cylindrical titanium alloy implant is designed to be placed between any of the third to seventh cervical vertebrae to provide immediate stability and promote fusion between vertebral bodies. According to Rich Lunsford, Sulzer Spine-Tech president, "Most surgeons prefer to use bone harvested from the patient in cervical spinal fusion procedures. Due to its unique design, BAK/C collects local bone during implant insertion, resulting in autograft without the need for bone harvest from the patient's hip."

According to the company, results of multicenter clinical studies showed significantly higher fusion rates at every follow-up interval for BAK/C patients when compared with those for patients who had an anterior cervical diskectomy and fusion. There were also fewer complications reported by those receiving the BAK/C device—17% compared with 25% in the control group.

Another technology, developed as a nonfusion alternative for treating degenerative disk disease, is currently being studied at 10 centers in the United States. The investigational device from Link Spine Group Inc. (Branford, CT), the SB Charité Intervertebral Dynamic Disk Spacer, provides total disk replacement in the lumbar spine. Disk replacement is viewed as a desirable alternative for some patients—particularly those who are active adults.

The U.S. study recently received attention when 41-year-old triathlete Karl Nusch was treated at the Cedars-Sinai Medical Center Institute for Spinal Disorders (Los Angeles) using Link's SB Charité device. Nusch's treatment underscores one of the advantages believed to result from total disk replacement.

Patients who undergo fusion surgery must restrict their motion for up to a year. In contract, patients who receive artificial disks are encouraged to be mobile right away, according to Nusch's surgeons, John J. Regan, MD, director of research and education at the Cedars-Sinai Institute and Robert S. Bray Jr., MD, director of the institute.

The SB Charité prosthesis consists of two cobalt chromium alloy end plates with an ultra-high-molecular-weight polyethylene sliding core between. Says Brian Cameron, president of Link Spine Group, "It is important to note that the SB Charité device is made of the same materials that have been implanted in millions of patients having had total hip or knee replacement surgery—cobalt-chromium alloy and polyethylene. We know that these materials are well tolerated by the human body."

Commenting on the current U.S. studies, Cameron notes, "We will follow each patient for a minimum of two years before presenting the data to the FDA. We are looking for submission to the FDA sometime in early 2004."

Taking Aim on Neuromuscular Tremors

A novel method for analyzing the steadiness of a marksman's aim eventually may be useful in diagnosing and monitoring tremors in patients with certain neuromuscular disorders. Developed by researchers from Penn State and the University of Verona, Italy, the technique could provide the basis for a sort of steadiness profile or body tremor "fingerprint" for any individual.

Says Joseph P. Cusumano, MD, Penn State associate professor of engineering science and mechanics, "Such a 'fingerprint' can be useful in a clinical setting to diagnose and track the progression of a neuromuscular disorder or injury, or the recovery from such a disorder or injury."

Developed by Cusumano and coinvestigator Paola Cesari, MD, director of the University of Verona Movement Science Laboratory, the new analysis technique entails use of video cameras to collect movement data from a person shooting at a target. The subject's movements are then reduced to their basic elements, which enables the researchers to determine how and why tremor varies as the person adjusts his or her joint angles to try to maintain a steady aim. Cusumano and Cesari combined a method of statistical data analysis, called principal component analysis, with stability analysis that relates tremor in the body joint positions to tremor of the target point. Cusumano says, "This combination of analyses is familiar in robotics but is new in the area of movement science."

According to Cusumano, "The new procedure allows the researchers to evaluate individual athletes and understand the specific configurations in which they hold their limbs to maximize the way in which the natural tremor in their body is controlled when they aim at a target."

The researcher explains that from this perspective, the natural tremor functions as an input at the body's joints. The output is the tremor or vibration at the task level—the target of the pointing. "We can use our method to show how this input-output relationship is affected by different limb configurations, which one can think of as 'aiming strategies,'" Cusumano says. "Thus, instead of just saying 'person X has more tremor than person Y,' one can adjust the position of the body and see its connection to performance in a very detailed way that is unique to each person. In short, an effective strategy will diminish the effect of body tremor at the task, while an ineffective one will attenuate tremor less, or even amplify it."

Use of the technique in a clinical setting is easy to imagine, according to Cusumano. "The calculations could be automated, and an appropriate user interface can be designed to enable the clinician to use the results without needing to get into all of the mathematics. The equipment required is very modest and readily available—compared to an MRI machine, for example." Such equipment would probably consist of some data acquisition system, such as a force platform and a 3-D motion analysis system, and a PC with appropriate software. He adds, "The method is noninvasive and can be performed easily on clothed subjects in an open, general-purpose space."

In their study, the researchers asked 16 people with varying degrees of expertise to aim an air pistol and shoot at a target. All subjects had a reflective marker attached to the tip of their gun, and on their wrist, elbow, shoulder, neck, head, and hip. Two optoelectrical cameras equipped with infrared illuminators tracked the markers and collected movement data. Using a computer, the researchers analyzed each image from the cameras and extracted the position of each marker as a function of time to produce a data stream.

While the group has performed studies only on athletes so far, they are currently planning to look at Parkinson's disease patients next year. Cusumano notes that the researchers have "an affiliation with a hospital in Italy that will allow us to explore purely clinical issues related to eventual application."

Says Cusumano, "The main scientific problem that we need to address with the experiments on Parkinson's subjects is to examine the details of the coordination patterns adopted by individuals to manage tremor, and identify different categories of adaptations. Because our method does much more than just quantify tremor, it is a tool that should enable us to see the differences needed for such categorization, which is the first step in the direction of clinical application."

The researcher explains that current screening tests require individuals to accomplish some basic task, such as pointing or standing, possibly with impediments or under different perceptual conditions. The subject's performance is then evaluated according to different qualitative criteria. "Using our analysis method, we aim to make such screening tests both more comprehensive as well as more quantitatively precise," he says.

The researchers suggest that there are three stages at which the technique may eventually be applied—diagnosis, prognosis, and treatment. Cusumano comments, "In the short term we are looking primarily at just the identification of pathologies and the tracking of their course. Even for that, we need at least five years of hard work since the clinical testing has not even been begun. Further down the road, prognostic and therapeutic applications can be envisaged."

Copyright ©2001 Medical Device & Diagnostic Industry