Taffy Bowman, CPO
Adjustable dynamic response (ADR) is a new concept for most orthotists. The ability to store and release energy that is adjustable for the individual or for changing gait patterns has not received a lot of attention. In the prosthetic field, we have been talking about the ability to offer dynamic response since the introduction of dynamic-response feet in the mid-1980s.1 Dynamic response prosthetic feet were designed to address the limitations of SACH and single-axis feet. That is, patients found SACH and single-axis feet to be too stiff to permit comfortable ambulation at more than a moderate pace.1 Dynamic response feet address this limitation and are now embraced by clinicians and patients as being the preferred feet for not only highly active amputees, but also for those who simply desire improvement for routine daily walking. We can apply our dynamic response experience used in the prosthetic field to our understanding of using ADR in orthotics.
The use of ADR in orthotic management stemmed from many of the same reasons as prosthetic dynamic-response feet. Typically, solid ankle design AFOs and drop lock or bail style knee joints are too restrictive for patients, while free motion may not provide enough stability. Rigid stops may be too abrupt to allow a smooth rollover. Dorsi-assist joints may provide an increased toe pickup during swing but not facilitate smooth rollover during stance. Selecting the appropriate trim lines, ankle, and/or knee components for patients depends more upon the experience of the treating clinician than on scientific rationale. Matching the involved weakness of patients with the perfect orthosis sometimes becomes a matter of trial and error, or at least adjustment and modification, for maximum improvement in the patient's gait. ADR for use in orthotic management has been developed to help address these limitations. ADR is the result of the marriage of gait analysis and the development of compensating orthotic technologies to address gait deviations seen throughout the gait cycle, particularly during stance.
The stance phase of gait entails 60 percent of the gait cycle. Because stance is where patients spend most of their time during ambulation, this area deserves considerable attention when considering orthotic management. According to Perry, the primary function of the muscles during stance is to stabilize the joints as the body weight progresses over the supporting limb.2 In normal gait, internal muscles successfully restrain the torque being applied to the limb (internal or supply torque) by the external ground reaction forces (external or demand torque). In pathological gait, the supply torque fails to respond appropriately to the demand torque. Shock absorption of the limb is compromised due to inadequate muscle response. Providing a means of balancing internal torque supply with external torque demand during the stance phase of gait is the primary focus of ADR.
ADR can be viewed as a marriage between inherently weak musculature with an external source of torque restraint. By marrying muscles that are not able to properly respond to ground reaction forces with an external component, we aim to achieve a union of balanced torque responses. This union allows patients with pathological gait the ability to have a gait pattern more similar to normal. Also, knee and ankle motion does not have to be compromised. Ultraflex's UltraSafeStep™ ankle joint allows 0-40 degrees of dorsiflexion and plantarflexion, and the UltraSafeStep knee joint allows 0-30 degrees degrees of knee flexion during stance. Ultraflex's UltraSafeStep knee and ankle components allow range of motion (ROM) to occur as close to normal throughout the gait cycle, yet be dynamically constrained as needed to prevent instability.
A traditional double-action ankle joint (figure 1) most commonly utilizes compression springs in the posterior channel to provide a dorsiflexion assist. Two springs used in combination with each other (medial and lateral) provide approximately 18 in./lb. of toe pickup.3 This method is often very effective in promoting clearance of the foot during swing. However, the design is not intended to nor does it provide appropriate torque restraint for stance phase control. In addition, a rigid stop is commonly used in a DAAJ to prevent the foot from slapping during the initial part of the stance phase. This ground reaction force in turn goes from the ankle to the knee.3
The Ultraflex UltraSafeStep ankle joint Figure 2 uses elastomers (figure 2) in the anterior and posterior channels of the component to restrain the tibialis anterior during loading response and the gastroc-soleus complex during terminal stance. The torque response for these elastomers provides 0-240 in./lb. for the tibialis anterior and 0-360 in./lb. for the gastroc-soleus complex. The elastomers allow for shock absorption and preventing ground reaction forces from adversely effecting more proximal joints.
For the most part, stance control orthoses (SCOs) lock the knee joint to provide knee stability during stance and unlock during swing to promote more natural ROM, flexion of the knee, and foot clearance. SCOs are designed primarily for patients with isolated quad weakness, so patients with more involved lower-extremity weakness are often excluded from being candidates for such orthoses. In contrast, the Ultraflex UltraSafeStep knee joint is designed specifically for use on patients with more involved lower-extremity weakness, which is far more common in clinical practice.
Looking at the data for sagittal plane ROM at the knee during stance, in normal gait the knee typically goes from 3 to 18 degrees during loading response and near 40 degrees by pre-swing (figure 3).
The ADR knee joint allows from 0-30 degrees ROM available for both the stance and the swing phases of gait. Elastomer bumpers to augment the quadriceps function dampen the ROM. If a patient needs maximum stability in the initial part of the rehab process, the joint can be locked in full extension. As the patient gains strength throughout the rehab process, the joint can be adjusted to allow more ROM to mimic more normal gait.
ADR and carbon fiber technologies can offer a very successful combination for the right patients. Carbon fiber offers increased strength, decreased weight, increased intimacy of fit, and better translation of forces to orthotic componentry than standard plastics.
In a recent case study, a patient was converted from a traditional plastic KAFO with limited motion to an Ultraflex KAFO with ADR with promising results. The Ultraflex KAFO demonstrated how ADR technology provides stance support at both the knee and the ankle dynamically. This minimizes compensations while allowing more normal knee-ankle-foot biomechanics (knee flexion and ankle-foot rollover) to maximize speed at reduced energy cost. This case study will be presented at the 2008 Annual Meeting and Scientific Symposium in Orlando, Florida.
ADR was originally developed for the changing needs common to stroke survivors. As patients progress with their rehabilitation program, it is common to see varying amounts of strength, balance, and coordination return to the patient. The technology allows for increased stability in the early phases of rehabilitation and less restriction of available muscle use in the latter phases. ADR not only suits the needs of stroke survivors, but almost any patient affected with gait inefficiencies such as quadriceps weakness, paralytic equinus, or crouch gait can benefit.
ADR represents an exciting area of technological advancement in the field of orthotics. By understanding how normal gait occurs and how we want to fully address the gait cycle in individuals with pathological gait, we can implement a more thorough approach to gait management. Ultraflex's UltraSafeStep knee and ankle components offer patients dynamic stability and safety without limiting ROM or use of inherent muscle strength. As orthotic clinicians, it is a privilege to offer a technologically advanced solution that focuses more on the ability of the patient than the disability.
For more information on Ultraflex UltraSafeStep Technology, contact Ultraflex's Clinical and Technical Support at 800.220.6670.
Michael JW. "Prosthetic Suspensions and Components." Atlas of Amputations and Limb Deficiencies. Third Edition. 2004; 33:409-427.
Perry J. "Ground Reaction Force and Vector Analysis." Gait Analysis Normal and Pathological Function. 1992; 19:413-429.
Lunsford T. Orthology: Pathomechanics of Lower-Limb Orthotic Design. 1998; 20-34.
Taffy Bowman oversees Clinical Affairs at Ultraflex Systems Inc., located in Pottstown, Pennsylvania, where she is responsible for education, research, and patient care. Bowman is a graduate of Northwestern University's Prosthetic and Orthotic Certificate programs and has been in the profession for 12 years. She is a member of the American Academy of Orthotists and Prosthetists, the Association of Children's Prosthetic-Orthotic Clinics, and the American Academy for Cerebral Palsy and Developmental Medicine.