Rancho Los Amigos Develops Innovative Technology

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Orthotics has taken a page from prosthetic technology. A research team from Rancho Los Amigos, Downey, California, has developed an AFO with dynamic dorsiflexion control similar to what has been achieved by many devices in lower-limb prosthetics.

The research team, which included Roger Weber, CPO, Ronan Reynolds, Samuel Landsberger, ScD, and Donald McNeal, PhD, used biomechanics and analysis methods to create the posterior strut AFO with controllable dorsiflexion resistance.

The research also has helped in developing a promising KAFO design.

The Challenge

"Our challenge was to develop a dynamic orthosis that is light in weight and cosmetically appealing, while allowing independent control of plantarflexion and dorsiflexion resistance, with dorsiflexion resistance being both dynamic and nonlinear," Weber explained in a presentation during the 2005 Annual Meeting and Scientific Symposium of the American Academy of Orthotists and Prosthetists (the Academy).

Hinged Vertebrace with progressive dorsistop and light shockcord dorsiflexion assist for patients with quadriceps weakness.
Hinged Vertebrace with progressive dorsistop and light shockcord dorsiflexion assist for patients with quadriceps weakness.

"Additionally, we wanted an orthosis that could be custom-modified for an individual's height, weight, motor deficit, and activity level. Prosthetics has handled these challenges before, but with orthotics we have additional challenges such as strict space and weight limitations, and limitations on a patient's 'gadget tolerance.'"

The team started with the question, "What does an energy-storing 'graphite' prosthetic system do?" The answer, they found, is: generally two main functions. These functions are 1) to control weight acceptance during initial heel contact, and 2) to controllably deflect in dorsiflexion and store energy from mid-stance to toe-off. Additionally, hybrid prosthetics generally have some inversion, eversion, and rotary control.

The need for soft initial heel contact is even more important in orthotics than it is in prosthetics, because many orthosis users have proximal weakness. "If the ankle forces at initial contact are not managed, a flexion moment may be generated at the knee, and at the hip, which the wearer may not be able to control." Thus, there must be a relatively soft heel or the ability to allow plantarflexion during loading response to manage these forces.

The Solution

Non-hinged Vertebrace with progressive dorsistop and stiff dorsiflexion assist for patients with strong quadriceps.
Non-hinged Vertebrace with progressive dorsistop and stiff dorsiflexion assist for patients with strong quadriceps.

The Rancho team developed what they call "The Vertebral Orthosis," which somewhat replicates the spine's vertebral column. The orthosis has several distinct components. First is the main support, which consists of a pre-manufactured graphite strut that is selected based on patient requirements, such as weight, activity, etc.

Ideally, this will conform to the proper plantar-resist/ dorsi-assist needed by the patient. However, if necessary, a mechanical posterior articulation is incorporated with an integrated dorsiflexion assist. Alternating graphite struts, with some crossing the ankle joint and others not crossing, also can be used to create plantarflexion and dorsiflexion resistances independent of one another, Weber explained.

So how is the correct amount of dorsiflexion resistance for specific dorsiflexion angles and input loads figured out and achieved?

A quantitative process has been developed. Using this process, the team can predict the required dorsiflexion resistance for a particular patient and custom-engineer the orthosis to generate this resistance.

To achieve this, the orthosis utilizes segmented sections between the foot shell and calf which replicate "vertebral bodies." The graphite strut passes through the posterior area, linking the segments together with a flexible structure. Along the medial and lateral parameters a channel is created, which can be used with elastic bands for increased dorsiflexion assist, as well as aid in the alignment of the vertebral bodies during loading. Based on the required dorsiflexion resistance, spacing between vertebral bodies that sequentially close under load has been calculated to allow for non-linear dorsiflexion resistance without terminal collapse. This, therefore, creates a dynamic ground reaction knee stabilizing orthosis.

Several versions of the "Vertebral Orthosis" have been developed, which allow each orthosis to have independent plantar/dorsiflexion in a controlled and quantifiable manner, Weber said. At the time of the Academy presentation, clinical trials had been performed with five subjects and evaluated in a pathokinesiology lab after two months of usage. The results are currently being analyzed.

A grant from the National Institute on Disability and Rehabilitation Research (NIDRR) of the US Department of Education supported this research.

KAFO: Knee Stability

During gait, the normal human knee flexes during loading response and during swing. However, the research team realized that existing knee braces for patients with quadriceps weakness flex only at loading response, only at swing, or not at all. They came to the logical conclusion that a brace that flexes at both times may improve the velocity and efficiency of gait.

During normal gait, the knee flexes to an angle of 17 degrees, and during swing it flexes to an angle of 60 degrees, Ronan Reynolds noted. This requires significant quadriceps strength; however if a person's quadriceps are weakened below a grade 3, due to such conditions as spina bifida, muscular dystrophy, polio, or cerebral palsy, KAFOs are commonly prescribed.

Three types of knee joints are available for KAFOs, said Reynolds. The first type does not bend at all during the gait cycle, such as a drop lock. These have a sleeve that slides over and locks a simple hinge. To sit down, the patient raises the sleeve and the joint can then rotate.

The second type bends at loading response. One example bends at loading response, and the knee is supported by a coil spring so it doesn't collapse. During swing, this spring resists flexion and locks the knee in extension. The third type is locked during loading response but unlocks during swing.

None of these joints allow knee flexion during both loading response and swing, as does the normal human knee, Reynolds pointed out. Not allowing flexion at loading response may increase the impact loads on hip and the knee, and delay tibial advancement and foot flat, he explained. Not allowing flexion during swing usually forces circumduction of the leg for toe clearance, which may cause slower and less efficient gait. To solve these problems, the Rehabilitation Engineering Program has developed a KAFO that stably allows knee flexion at loading response and during swing.

A normal knee is naturally unstable while flexed and needs to be supported with muscles to prevent collapse. Thus, if a person is weak or paralyzed, the muscles need to be replaced with a mechanism. This mechanism should apply a moment across the knee during loading response that varies nonlinearly with flexion angle, Reynolds explained. Additionally, it must lock before initial contact and unlock before swing.

The team used the vertebrace technology developed in the AFO project described earlier in this article to provide a non-linear spring for use as an extension assist and an extension stop on the knee joint. This spring can provide a predictable non-linear stiffness tailored to a particular patient's requirements, according to Reynolds. The team has added to this spring a locking/unlocking linkage driven by the dorsiflexion/plantarflexion angle of the ankle. KAFOs using this design are currently being developed and evaluated, Reynolds added. This work also was supported by a grant from the NIDRR.