O R T H O T I C T E C H N O L O G Y

hat is Adjustable DynamicResponse? In the prostheticfield, we have been talking

about the ability to offer dynamicresponse since the introduction ofdynamic-response feet in the mid-1980s1. Dynamic response prostheticfeet were designed to address the limi-tations of SACH and single-axis feet.That is, patients found SACH and sin-gle-axis feet to be too stiff to permitcomfortable ambulation at more than amoderate pace1. Dynamic response feetaddress this limitation and are nowembraced by clinicians and patients asbeing the preferred feet for not onlyhighly active amputees, but also thosewho simply desire improvement forroutine daily walking. The practitionercan use what exists for dynamicresponse in the prosthetic field andrelate it to an understanding of using

adjustable dynamic response (ADR) inorthotics.

The use of ADR in orthotic manage-ment stemmed from many of the samereasons for use of prosthetic dynamic-response feet. Typically, solid ankledesign AFOs and drop lock or bail styleknee joints are too restrictive forpatients, while free motion may notprovide enough stability. Rigid stopsmay be too abrupt to allow a smoothrollover. Dorsi-assist joints may providean increased toe-pickup during swing,but not facilitate smooth rollover dur-ing stance. Selecting the appropriatetrim lines, and ankle and/or knee com-ponents for patients relies more on theexperience of the treating clinician thanon scientific rationale. Matching theinvolved weakness of patients with theperfect orthosis sometimes becomes amatter of trial and error, or at least

adjustment and modification, for maxi-mum improvement in the patient’s gait.ADR for use in orthotic managementhas been developed to help addressthese limitations. ADR is the result ofthe marriage of gait analysis and thedevelopment of compensating orthotictechnologies to address gait deviationsseen throughout the gait cycle, particu-larly during stance.

Orthotic Managementin the Stance Phase

The stance phase of gait entails 60percent of the gait cycle. Because stanceis where patients spend most of theirtime during ambulation, this areadeserves considerable attention whenconsidering orthotic management.According to J. Perry, the primary func-tion of the muscles during stance is to

Managing Gait Deviations withAdjustable Dynamic Response

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Adjustable Dynamic Response (ADR) is a new concept for most orthotists.The abilityto store and release energy that is adjustable for the individual or for changing gaitpatterns has not received a lot of attention.

W

By:Taffy Bowman, CPOUltraflex Systems, Clinical Affairs

stabilize the joints as the body weightprogresses over the supporting limb2.In normal gait, internal muscles suc-cessfully restrain the torque beingapplied to the limb (internal or supplytorque) by the external ground reactionforces (external or demand torque). Inpathological gait, the supply torquefails to respond appropriately to thedemand torque. Shock absorption ofthe limb is compromised due to inade-quate muscle response. Providing ameans of balancing internal torquesupply with external torque demandduring the stance phase of gait is theprimary focus of ADR.

Marriage of Supplyand Demand

ADR can be viewed as a marriagebetween inherently weak musculaturewith an external source of torquerestraint. By marrying muscles that arenot able to properly respond to groundreaction forces with an external com-ponent, we aim to achieve a union ofbalanced torque responses. This unionallows patients with pathological gaitthe ability to have a gait pattern moresimilar to normal. Also, knee and anklemotion does not have to be compro-mised. The USS™ ankle joint fromUltraflex allows 0-40º of dorsi-flexionand plantar-flexion and the USS kneejoint allows 0-30º degrees of knee flex-ion during stance. Ultraflex’s UltraSafe-Step knee and ankle components allowROM to occur as close to normalthroughout the gait cycle, yet be

dynamically constrained as needed toprevent instability.

Double-Action AnkleJoint Departure

A traditionaldouble-action anklejoint (DAAJ) mostcommonly utilizescompression springsin the posterior chan-nel to provide a dorsi-flexion assist (Fig.1). Twosprings used in combina-tion with each other(medial and lateral) pro-vide approximately 18 in/lbs of toe pickup3. This method is often very effectivein promoting clearance of the foot dur-ing swing. However, the design is notintended to provide appropriate torquerestraint for stance phase control. Inaddition, a rigid stop is commonlyused in a DAAJ to prevent the footfrom slapping during the initial part ofthe stance phase. This ground reactionforce in turn goes from the ankle to theknee3.

The Ultraflex USS ankle joint useselastomers (Fig. 2) in the anterior and

posterior chan-nels of the com-ponent torestrain the tib-ialis anteriorduring loadingresponse andthe gastroc-soleus complex

during terminal stance. The torqueresponse for these elastomers provides0-240 in/lbs for the tibialis anterior and0-360 in/lbs for the gastroc-soleuscomplex. The elastomers allow forshock absorption, preventing groundreaction forces from adversely effectingmore proximal joints.

Ultraflex Knee JointDifference

For the most part, Stance ControlOrthoses (SCOs) lock the knee joint toprovide knee stability during stanceand unlock during swing to promotemore natural ROM, flexion of the hipand foot clearance. SCOs are designedprimarily for patients with isolatedquad weakness, so patients with moreinvolved lower extremity weakness areoften excluded from being candidatesfor such orthoses. In contrast, theUltraflex USS knee joint is designedspecifically for use on patients withmore involved lower extremity weak-ness, which is far more common inclinical practice.

Looking at the data for sagittal planeROM at the knee during stance, in normal gait the knee typically goesfrom 3º to 18º during loading responseand near 40º by pre-swing (Fig.3).

The ADR knee joint allows from 0-30º ROM available for both thestance and the swing phases of gait.Elastomer bumpers work to augmentthe quadriceps function and dampenthe ROM. If a patient needs maxi-mum stability in the initial part of

Alignment 2009 53

Ultraflex ADR CAFO demonstrating the five phases of stance: Initial Contact, Loading Response, Mid-Stance, Terminal Stance and Pre-Swing.

Figure 1

Figure 2

their rehab process, the joint can belocked in full extension. As they gainstrength throughout their rehabprocess, the joint can be adjusted toallow more ROM to mimic morenormal gait.

ADR PerformancePowered By Carbon Fiber

ADR and carbon fiber technologiescan offer a very successful combina-tion for the right patients. Carbonfiber offers increased strength,decreased weight, increased intimacyof fit, and better translation of forcesto orthotic componentry than stan-dard plastics.

In a recent case study, a patient wasconverted from a traditional plasticKAFO with limited motion to a USSKAFO with ADR with promisingresults. The USS KAFO demonstratedhow ADR technology provides stancesupport at both the knee and theankle dynamically. This minimizescompensations, while allowing morenormal knee-ankle-foot biomechan-ics (knee flexion and ankle-foot roll-over) to maximize speed at reducedenergy cost.

Who Can Benefit from ADR?

ADR was originally developed for thechanging needs common to stroke sur-vivors. As patients progress with theirrehabilitation program, it’s common tosee varying amounts of strength, bal-ance and coordination return to thepatient. The technology allows forincreased stability in the early phases ofrehabilitation and less restriction ofavailable muscle use in the latter phases.ADR not only suits the needs of strokesurvivors, but almost any patient affect-ed with gait inefficiencies such asquadriceps weakness, paralytic equinusor crouch gait can benefit.

Focusing on Ability,not the Disability

ADR represents an exciting area oftechnological advancement in the field oforthotics. By understanding how normalgait occurs and how we want to fullyaddress the gait cycle in individuals withpathological gait, we can implement amore thorough approach to gait man-agement. Ultraflex’s USS knee and anklecomponents offer patients dynamic sta-bility and safety without limiting ROM

54 Alignment 2009

or use of inherent muscle strength. Asorthotic clinicians, it’s a privilege to offera technologically advanced solution thatfocuses more on the ability of the patientthan the disability.

For more information on UltraflexUSS™ Technology, contact Ultraflex’sClinical and Technical Support at 1-800-220-6670.

References:1Michael JW. Prosthetic Suspensions andComponents. Atlas of Amputations and LimbDeficiencies. Third Edition. 2004; 33:409-427.

2Perry J. Ground Reaction Force and VectorAnalysis. Gait Analysis Normal andPathological Function. 1992; 19:413-429.

3Lunsford T. Orthology: Pathomechanics ofLower-Limb Orthotic Design. 1998; 20-34.

About the Author:Taffy Bowman oversees ClinicalAffairs at UltraflexSystems Inc., locatedin Pottstown, Penn-sylvania, where she isresponsible for educa-tion, research andpatient care. Bowman is a graduate ofNorthwestern University’s Prosthetic andOrthotic Certificate programs and has beenin the profession for 13 years.

O R T H O T I C T E C H N O L O G Y

Figure 3