American Academy of Orthotists & Prosthetists

Normalizing Shank Kinematics with Adjustable Dynamic Response™ (ADR™)

• Keith Smith, CO, LO, FAAOP
• Taffy Bowman, CPO

The term "shank" is often used in gait labs and refers to the lower part of the limb between the knee and the ankle. Normalizing shank kinematics, or shank motion, is an important biomechanical principle that is critical to optimizing gait function. Normalizing the kinematics of the shank throughout gait with the use of orthotic management has received a fair amount of attention, particularly due to the work done by Owen¹ and Bowers² at The University of Strathclyde, Glasgow, Scotland. Likewise, the concept of shank kinematics has also been referred to as "tibial advancement in gait" by Perry.³ In protocol development for orthotic management of the limb during stance phase (when the foot is on the ground and emphasis is on optimizing tibial progression over the foot in the sagittal plane), as orthotists we may ask, "What type of AFO allows us the ability to normalize shank kinematics or tibial advancement?"

Owen points out, "Children with pathological gait have abnormal shank kinematics. Normalizing shank kinematics produces the best chance of achieving optimum thigh and trunk kinematics and knee and hip kinetics."¹ The Strathclyde Approach, as taught by clinicians such as Owen and Bowers, focuses on the angle of the shank throughout stance relative to the floor. If we control the angle of the shank, or the kinematic, we then influence the kinetics, or forces associated with gait. This concept offers us much possibility at helping to normalize pathological gait with orthotic management.¹

The "Tuning" Approach: Angle of the Shank Relative to the Floor

The Strathclyde Approach uses the term Ankle-Foot-Orthosis-Footwear-Combination (AFOFC). As the name suggests, emphasis is placed both on the AFO and the footwear. By "tuning" the AFOFC relative to the vertical, it allows the practitioner to take control of shank kinematics. The term "tuning" refers to the adjustment of the heel-sole differential of the shoe to produce an effect on shank kinematics. Manipulating kinematics results in influencing kinetics. This approach uses shoe wedges and modifications to manipulate the angles of the shank in the AFOFC. An algorithm for AFOFC design has been carefully developed for this approach and is currently being used in gait labs.³ For example, a patient presenting with a fixed equinus contracture or knee-flexed position may be fitted with a solid AFO set in plantarflexion with a shoe wedge to promote an inclined shank at midstance.

The "Traditional" Approach

Over the years, a variety of AFO designs have emerged in an effort to come up with the best solution or produce the most effective outcome. For instance, a patient who exhibits significant weakness would traditionally be fit with a design that is more rigid, with stiffer trimlines. If the patient needs less control, a more flexible design would be chosen. This variance in strength leads to some patients getting a hinged design that allows, assists, or stops certain motions while others get a solid design that stops most motion in the sagittal plane of the tibia over the foot. Shoe wedges or lifts to augment the final tibial angle to the ground may or may not be implemented. At this time, there is no set algorithm that can be used with the traditional approach. Further, there is much art and variation in the traditional approach, and the authors suggest more science is needed in this area.

The Goal of AFOs for Children

The goal of AFOs for children is to give them improved function while still maintaining the priorities of normal gait. Gage addresses gait priorities as (1) stability in stance; (2) clearance in swing; (3) preposition of the foot at initial contact; (4) adequate step length; and (5) energy conservation.⁵

It is important to note that the first priority, according to Gage, is stability in stance. Therefore, stability in stance or, stated another way, normalizing shank kinematics, should be the number-one priority in orthotic gait management.

Challenges of Traditional AFO Designs

Gage points out some of the challenges with traditional AFO designs. A leaf-spring AFO, for example, can be used to control mild equinus and or valgus positioning during swing, and it may also position the foot during terminal swing for initial contact, but patients with more significant equinus may not be adequately controlled with this more flexible design. A rigid AFO or an AFO with a plantarflexion block may control stance phase deformities such as varus, valgus, or equinus, but the rigidity can be counterproductive in terminal stance, not allowing plantarflexion and consequently blocking acceleration for third rocker. Hinged AFOs with plantarflexion stops and free dorsiflexion may promote function in children because of the less restrained design, but may encourage crouch gait in the long term.⁵

The Ideal Orthosis

Gage states that the ideal orthosis is "a device that would control the position of the foot in swing phase, initial contact and loading response, but leave the ankle completely unencumbered during midstance and terminal stance".⁵

Development of Adjustable Dynamic Response (ADR)

Utilizing the elements of Gage's ideal orthosis, in conjunction with the importance of normalizing shank kinematics as demonstrated by the Strathclyde Approach, provides the research background for the development of Adjustable Dynamic Response™ (ADR™) technology. This technology provides patients with a range of motion (ROM) that is stabilized, thereby limiting the compromises often associated with traditional orthoses. ADR technology provides adjustable muscle augmentation, stability in stance, smooth rollover, and clearance in swing.

ADR has received an increasing amount of attention over the last several years since the 2004 introduction of UltraSafeStep™ knee and ankle components developed by Ultraflex® for management of adult pathological gait such as post-stroke and post-polio. ADR utilizes elastomer technology to dampen or restrain ROM during gait, versus holding or stopping motion. The component resists motion rather than stopping it all together.

Introduced in May of 2009, UltraSafeGait™, the pediatric ADR version of the UltraSafeStep, is specifically sized and designed for patients weighing 110 lb. (50kg) or less. The anterior and posterior elastomer channels, as shown in Figure 1, allow for 140 in./lb. of torque restraint per channel. This amount of torque restraint is capable of augmenting the eccentric work of the tibia and the gastroc-soleus during stance. ADR elastomer technology, compared to spring technology that offers 15-18 in./lb. of toe pick-up for swing phase, is in a class of its own.

Figure 1: UltraSafeGait Pediatric ADR component

UltraSafeGait ADR technology was designed to give patients stability as well as motion in an AFO component. This stability and motion is obtained by making adjustments to the component during observational gait analysis in the clinic setting by increasing or decreasing resistance. The clinician has the ability in the field to fine tune first, second, and third rocker in real time, influencing shank kinematics with simple component adjustments without removing the AFO. For example, a patient who has a crouched gait pattern could have dorsiflexion resistance increased in the anterior channel as range of motion of the knee is increased. Or, a patient who hyperextends the knee could have the resistance increased in the posterior channel to decrease this tendency. Opposed to "tuning" a solid AFO with heel wedges to control shank kinematics, ADR allows you to control shank kinematics by providing adjustable resistance within a component.

Clinical Example: Managing Multiple Orthotic Goals

Our patient is an 8-year-old boy born with spina bifida, GMFCS level III; he is non-verbal but enjoys activities such as swimming, T-ball, and playing video games. He has undergone two separate surgeries to remove two different spinal tumors at the ages of four and seven. He presents with significant spasticity in his lower limbs causing ROM deficits, gross weakness of the lower limb, and significant crouch during gait. The patient began receiving orthotic management when he was one year old and has had a number of orthoses over the past several years. Past orthotic management consisted of primarily ground-reaction AFOs, either solid-ankle designs set at 90 degrees or hinged designs allowing the angle to be locked or set in a fixed position to accommodate his hamstring tightness.

Figure 2a: Initial fitting in March 2009. (USG ankle joint set with anterior elastomer compressed to create dorsiflexion restraint/knee extension moment.)

Figure 2b: Follow-up appointment October 2009. Patient demonstrates increased knee extension at terminal stance and increased step length. (USG ankle joint set with increased anterior elastomer compression after patient's knee extension ROM has increased.)

Goal 1: Improving ROM

Currently, he has been prescribed an Ultraflex dynamic resting stretching knee orthosis for his right side to address his popliteal angle, which measured -35 degree R2 prior to intervention. At the three-month follow-up visit, he progressed to a -20 degree R2 popliteal angle, demonstrating a 15-degree increase in knee ROM. His parents report that the patient wears his stretching knee orthosis at night while he is sleeping and sometimes during homework. Average wear time is 8-10 hours per day at a tension setting of five. Both measurements were taken prior to him receiving botulinum toxin type A, which he receives every three months.

Goal 2: Provide Stability in Stance while Normalizing Shank Kinematics

In addition to the patient's nighttime knee orthosis, he was recommended for bilateral floor-reaction style ADR AFOs to improve stability and control crouch during gait. The ADR ankle joints were initially set with resistance from the anterior channel to decrease his tendency to ambulate in a crouched position. As the forefoot is loaded, the ADR joints allow for adjustable resistance into dorsiflexion, instead of being held in a fixed position. As range of motion at the knee has increased, his treating orthotist has been able to increase the resistance in this anterior channel, which has lead to a reduction in the crouch pattern. (See Figures 2a and 2b.) The distinguishing factor in his new treatment modality is that instead of being in a fixed ankle position, the ADR AFOs allow an adjustable ankle-dorsiflexion resistance. As the patient gains knee ROM, the resistance can be increased at the ankle to create an improved knee extension/ankle plantarflexion couple.

Future Research

The UltraSafeGait ankle-joint system is currently under a prospective study to examine the efficiency of the technology with patients with cerebral palsy in treating crouch-gait patterns as well as equinus with knee hyperextension in the sagittal plane. Future research looks to develop outcome measures that would increase functional ambulation for the patient with crouch-gait patterns or equinus with knee hyperextension with a focus on resistance rather than limitations.

Clinical Significance

This technology may have created a tool to provide dynamic resistance to motion and adjust shank kinematics in a clinical setting. It also allows customized solutions to unique individual patient presentation and pathologies. Adjustable dynamic response is a significant clinical advancement in the field of orthotic management for controlling shank kinematics.

References

1. Owen E. Tuning of ankle-foot orthosis combinations for children with cerebral palsy, spina bifida and other conditions. Proceedings of European Society of Movement Analysis in Adults and Children (ESMAC) Seminars:pg. 4. 2004.

2. Bowers R, Meadows B. Use of an ankle foot orthosis to optimize hip and knee biomechanics following stroke. The Academy Today. 3(2):A10-11. 2007.

3. Owen E. A clinical algorithm for the design and tuning of ankle foot orthosis footwear combinations (AFOFCs) based on shank kinematics. Gait and Posture. 22(S):S36-37. (2005).

4. Perry J. Gait Analysis Normal and Pathological Function. Thorofare, NJ. Slack Inc. 1992.

5. Gage JR. The Treatment of Gait Problems in Cerebral Palsy: pg. 279. London. Mac Keith Press. 2004.

Keith M. Smith, CO, LO, FAAOP is a practicing orthotist employed at the Orthotic and Prosthetic Lab Inc. in St. Louis, Missouri, where he specializes in clinics in scoliosis and pediatrics with neurologic involvement. Smith has participated in and published with the American Academy of Orthotists and Prosthetists' first Clinical Standards of Practice Consensus Conference on the Orthotic Treatment of Idiopathic Scoliosis and Scheuermann's Kyphosis. He has been actively involved in research in the field, publishing numerous times in the Journal of Prosthetics and Orthotics as well as lecturing at numerous Academy as well as American Orthotic & Prosthetic Association (AOPA) meetings and functions. Smith won the Thranhardt honorarium at the Academy Annual Meeting in 2004 for his presentation on "A New Design for Scoliosis and its Coronal Plane Deviations." Smith is currently the president of the Academy.

Taffy Bowman , CPO, is employed by Ultraflex Systems Inc. where she serves at the director of clinical affairs. She oversees education, research, and patient care for the purposes of research and development. She is a graduate of Northwestern University's orthotic and prosthetic programs and been in the field for 14 years.

Earn PCE Credits from this article

Take the quiz at the Academy's Online Learning Center.