Design Of Ankle Foot Orthosis Research Articles

Techniques to measure rigidity of ankle-foot orthosis: A review

We performed this review to provide a clearer understanding of how to effectively measure ankle-foot orthosis (AFO) rigidity. This information is important to ensure appropriate orthotic intervention in the treatment of patients with pathological gait. The two main approaches to the investigation of AFO rigidity are (1) bench-testing analyses, in which an AFO is fixed or attached to a measurement device, and (2) functional analyses, in which measurements are taken while a subject is walking with an AFO in situ. This review summarizes and classifies the current state of knowledge of AFO rigidity testing methods. We analyzed the strengths and weaknesses of the methods in order to recommend the most reliable techniques to measure AFO rigidity. The information obtained from this review article would, therefore, benefit both clinicians and engineers involved in the application and design of AFOs.

What Variables Influence the Ability of an AFO to Improve Function and When Are They Indicated?

Children with spina bifida often present with functional deficits of the lower limb associated with neurosegmental lesion levels and require orthotic management. The most used orthosis for children with spina bifida is the ankle-foot orthosis (AFO). The AFO improves ambulation and reduces energy cost while walking. Despite the apparent benefits of using an AFO, limited evidence documents the influence of factors predicting the ability of an AFO to improve function and when they are indicated. These variables include AFO design, footwear, AFO-footwear combination, and data acquisition. When these variables are not adequately considered in clinical decision-making, there is a risk the AFO will be abandoned prematurely or the patient's stability, function, and safety compromised. The purposes of this study are to (1) describe the functional deficits based on lesion levels; (2) identify and describe variables that influence the ability of an AFO to control deformities; and (3) describe what variables are indicated for the AFO to control knee flexion during stance, hyperpronation, and valgus stress at the knee. A selective literature review was undertaken searching MEDLINE and Cochrane databases using terms related to "orthosis" and "spina bifida." Based on previous studies and gait analysis data, suggestions can be made regarding material selection/geometric configuration, sagittal alignment, footplate length, and trim lines of an AFO for reducing knee flexion, hyperpronation, and valgus stress at the knee. Further research is required to determine what variables allow an AFO to improve function.

Research Recommendations and Considerations

The State of the Science Conference on the effects of ankle-foot orthoses (AFOs) on balance concluded with a discussion of future recommendations and considerations for the topic. Recommendations and discussions were organized according to the four broad domains including 1) task or the activities most anticipated for a given patient care scenario, 2) AFO design or the physical characteristics of the provided intervention, 3) functional impairment or the diagnoses and presentations of the subjects, and 4) outcomes assessment or the established means by which the treatment effect will be formally observed and documented. Future research will be challenged by the considerable overlap of these domains with respect to individual balance considerations. The effect of AFOs on balance has been largely overlooked, both in clinical practice and research laboratories. Therefore, the need for future research in this area to inform clinical decision making is immense.

Evaluation of the contact forces developed in the lower limb/orthosis interface for comfort design

Ankle-Foot Orthoses (AFOs) are technical aids that promote locomotion and rehabilitation of individuals with gait pathologies. Every pathology has its own requirements and this has led to classical solutions that are far from optimal in terms of comfort and overall performance for restoring the human gait. Formal scientific approaches are therefore necessary to take full advantage of the available technological potential and produce more efficient modern devices that can significantly improve the quality of life of people with locomotion impairment. In this work, a computational multibody dynamics approach is adopted. A multibody model of an active AFO is developed and integrated in a whole-body multibody human model developed in the MATLAB environment. In the adopted procedure, normal gait motion data is used as input to the biomechanical model. The experimental data was obtained in the gait lab by acquiring the kinematic and kinetic data of a stride of a healthy female subject. The aim of this integrated model is to estimate the loads transmitted at the foot-leg-orthosis interface. To achieve this, it is essential to decide where the contact between the lower limb and the orthosis should occur, and what are the forces generated in such interface. A contact model between a sphere and a plane is applied together with a friction model to determine the contact forces, and the properties used for the surfaces in contact were based on the available data in the literature and on experimental tests. The results revealed that the contact pressures obtained are below the PPTs (Pain Pressure Thresholds), which represent the patient’s comfort. However, the pressure is dependent on the contact properties between surfaces, meaning that these must be experimentally determined for each material. It was also uncovered that the weight of the orthosis is an important issue in the design of an active AFO as it greatly influences the moments at the ankle, knee, and hip and, therefore, the patient effort when wearing the orthosis.

Effect of AFO Design on Walking after Stroke

This study was conducted to compare the effects of three ankle-foot orthosis (AFO) designs on walking after stroke and determine whether an ankle plantar flexion contracture impacts response to the AFOs. A total of 30 individuals, ranging from 6-215 months post-stroke, were tested in four conditions: shoes only (SH), dorsi-assist/dorsi-stop AFO (DA-DS), plantar stop/free dorsiflexion AFO (PS), and rigid AFO (Rigid). Kinematics, kinetics, and electromyographic (EMG) activity were recorded from the hemiparetic lower extremity while participants walked at a self-selected pace. Gait parameters were compared between conditions and between participants with and without a moderate ankle plantar flexion contracture. All AFOs increased ankle dorsiflexion in swing and early stance. Anterior tibialis EMG was reduced only in the PS AFO. Both PS and Rigid AFOs restricted ankle plantar flexion and increased knee flexion in loading. Peak ankle dorsiflexion in stance and soleus EMG intensity were greatest in the PS AFO. The Rigid AFO tended to restrict dorsiflexion in stance and knee flexion in swing only in participants without a plantar flexion contracture. Individuals without a contracture benefit from an AFO that permits dorsiflexion mobility in stance and those with quadriceps weakness may more easily tolerate an AFO with plantar flexion mobility in loading.

Effects of Clinically Prescribed Ankle Foot Orthoses on Ankle-Foot Roll-Over Shapes: A Case Series

ABSTRACT The purpose of this case series was to explore the effects of clinically prescribed ankle-foot orthoses (AFOs) (i.e., the orthosis an individual is provided by their health care team for everyday use) on the ankle-foot roll-over shapes (ROS) of persons with various pathologies. We hypothesized that persons for whom AFOs had been prescribed would have an abnormal ROS and that AFOs would make the ROS similar to that of able-bodied persons. Gait data were recorded from eight adults with unilateral involvement: five subjects (one with a common peroneal nerve injury, one with a subchondral talar cyst, one with an incomplete spinal cord injury, one with hemiplegia due to stroke, and one with postpolio) wore posterior leaf spring AFOs (PLS-AFOs); two subjects (with hemiplegia due to stroke) wore articulated AFOs with a plantar flexion stop and free dorsiflexion; and one subject (with hemiplegia due to stroke) wore a solid AFO. Participants walked with and without their AFO at their freely selected walking speed. “Normal” reference data were recorded from 10 able-bodied subjects of similar age walking at similar speeds. As hypothesized, ROS—as characterized by arc length and arc radius—was abnormal for all subjects when walking without an AFO. However, the prescribed AFOs were only able to partially restore ROS. Arc lengths were closer to normal with the AFO when compared to without, but changes in arc radius were less consistent, with only three subjects having radii that were closer to normal when the AFO was worn. Overall, there were smaller changes in ROS arc length and radius when PLS-AFOs were worn compared with articulated AFOs, consistent with the fact that PLS-AFOs are typically prescribed for those with less severe pathologies. ROS arc length and radius increased in all subjects with stroke when AFOs were worn. The results of this case series suggest that although clinically prescribed AFOs tend to improve ROS compared with walking without an AFO, they do not completely normalize it. Further research is required to assess the relationship between gait dysfunction, AFO design, and ROS.

EFFECTS OF PROSTHETIC MASS DISTRIBUTION ON MUSCULOSKELETAL SYSTEM DURING AMPUTEE GAIT

Ankle foot orthoses (AFOs) are designed to improve gait for individuals with neuromuscular conditions and have also been used to reduce energy costs of walking for unimpaired individuals. AFOs influence joint motion and metabolic cost, but how they impact muscle function remains unclear. This study investigated the impact of different stiffness AFOs on medial gastrocnemius muscle (MG) and Achilles tendon (AT) function during two walking speeds. We performed gait analyses for eight unimpaired individuals. Each individual walked at slow and very slow speeds with a 3D printed AFO with no resistance (free hinge condition) and four levels of ankle dorsiflexion stiffness: 0.25 Nm/°, 1 Nm/°, 2 Nm/°, and 3.7 Nm/°. Motion capture, ultrasound, and musculoskeletal modeling were used to quantify MG and AT lengths with each AFO condition. Increasing AFO stiffness increased peak AFO dorsiflexion moment with decreased peak knee extension and peak ankle dorsiflexion angles. Overall musculotendon length and peak AT length decreased, while peak MG length increased with increasing AFO stiffness. Peak MG activity, length, and velocity significantly decreased with slower walking speed. This study provides experimental evidence of the impact of AFO stiffness and walking speed on joint kinematics and musculotendon function. These methods can provide insight to improve AFO designs and optimize musculotendon function for rehabilitation, performance, or other goals.

Quantifying the Spring-Like Properties of Ankle-Foot Orthoses (AFOs)

In Brief To assess the ability of a specific orthotics stiffness tester to quantify the biomechanical properties of stiffness and energy return of three different ankle-foot orthosis (AFO) designs. Three different posterior leaf spring AFO designs (standard, chevron, carbon fiber) were fabricated in three different sizes and in three different stiffnesses. Efforts were made to standardize the design characteristics across the different styles to ensure uniformity. Each AFO was tested repeatedly with the orthotic stiffness tester. Stiffness was calculated as the average slope of the angle versus moment plot. Energy dissipation was calculated as the area inside the hysteresis loop. The device was found to be repeatable for stiffness, but not for energy storage. Speed did not affect stiffness calculations. Size was significant. Significant differences were found between stiffness categories (flexible, moderate, and stiff). The orthotic stiffness-testing device appears to be appropriate for use in studies that attempt to optimize orthosis-patient stiffness pairings. It is not adequate for assessing energy storage and return. We intend to match stiffness deficits of individual patients with AFOs of appropriate stiffness to normalize the midstance plantarflexor moment. We plan to improve the design of the orthotics tester to better assess the ability of the AFO to assist with power generation at push-off. This study assesses the ability of a specific orthotics stiffness-tester to quantify the biomechanical properties of stiffness and energy return of three different AFO de-signs. The orthotic stiffness-testing device appears to be appropriate for use in studies that attempt to optimize orthosis-patient stiffness pairings, leading the authors to plan to improve the design of the orthotics tester to better assess the ability of the AFO to assist with power generation at push-off.

Technical Note: Fabrication of a Dual-Axis Articulated Ankle-Foot Orthosis

In Brief Custom and prefabricated ankle-foot orthoses (AFOs) can either augment or hinder patients’ gaits, depending upon how they are made and aligned. To optimize patient function, it is necessary to accurately and effectively fit and align orthoses to individual patients’ anatomy and biomechanical characteristics. Unlike traditional AFOs, such as the posterior leaf spring AFO and the articulated ankle AFO with metal stirrup and dual uprights, the dual-axis AFO allows both the anatomical ankle and subtalar joint axes to function naturally and contribute to the motion of the lower limb and body throughout the gait cycle. The dual-axis AFO design follows a design originally proposed by Campbell et al. [Campbell J, Henderson W, Patrick D. UC-BL dual axis ankle-control system: casting, alignment, fabrication and fitting. Bull Prosthet Res 1969;10–11:184–214], incorporating a floating yoke containing an articulated ankle joint. The yoke and ankle joint are supported by struts mounted on an articulated subtalar joint attached to a stirrup on the shoe. The ankle and subtalar joints can be made with flexion/extension (inversion/eversion) stops and/or spring assists as required by the respective patient. The dual-axis AFO design allows a more natural, stable, energy-efficient gait. A dual-axis ankle-foot-orthosis allows the anatomical ankle and subtalar joint axes to function naturally and contribute to the motion of the lower limb and body throughout the gait cycle. Fabrication of a cost-effective and time-efficient dual-axis AFO is described.

Presentation 5: An investigation of foot alignment and support in ankle foot orthoses

Objective: To investigate the effect that ankle-foot alignment and foot support in ankle-foot orthoses (AFOs) may have on the gait of subjects with hemiplegia after stroke. Design: Test-retest. Setting: Motion analysis research laboratory. Participants: 20 participants with hemiplegia. Intervention: Subjects underwent 3 gait analyses, each 2 weeks apart. The first tested walking with a conventionally aligned AFO; the second tested walking with a heel-height compensated AFO with full-length footplate; and the third tested walking with a heel-height compensated AFO with three-quarter length footplate. Main Outcome Measures: We acquired bilateral kinematic, kinetic, electromyographic, and plantar pressure data, as well as subjective information from the subjects using a questionnaire. Results: Preliminary data from 7 subjects suggests that, compared with a shoes-only condition, all AFO conditions improved ankle position at initial contact and in swing, and, where knee hyperextension was present, reduced the onset and magnitude of the hyperextension. All AFO conditions also changed the internal knee moment from flexor to extensor, decreased the heel strike transient present in the vertical ground reaction force, and improved roll-over shape. Conclusions: Compared with the full length AFOs, the three-quarter length AFO provided the shortest roll-over shape and had the highest peak pressures in the midfoot. We believe that this study will give us a better understanding of the effect of ankle-foot alignment and foot support on hemiplegic gait, and may enable us to recommend more appropriate AFO designs.

Development of a Testing Apparatus for Structural Stiffness Evaluation of Ankle-Foot Orthoses

Quantitative analysis of ankle-foot orthosis (AFO) stiffness and impact-loading response could assist the orthotic industry and orthotists in fabricating and prescribing the most appropriate AFO design. Previous investigators have studied the flexibility of AFOs by using base plates fixed to the AFO and applying forces to the shank. However, when the footplate is fixed, the only regions of the AFO that are evaluated are the ankle and calf areas. These earlier studies are perhaps appropriate for current materials, such as polypropylene, that predominantly fatigue and fail in the flexibility zone, usually situated around the ankle region of the AFO. With the introduction of advanced composites applied to AFO fabrication, the ankle region can be strengthened by adding material, where needed, to prevent further fatigue or failure. However, other regions of the AFO may fail because of the relatively high modulus and strength characteristics of these advanced composites compared with metals and polypropylene. In this article, we attempt to demonstrate the utility of a new AFO apparatus that can test the structural displacement or stiffness of an AFO when it is subjected to static or impact loads. A series of tests of different AFO designs and materials was conducted to demonstrate the feasibility of this new apparatus. This apparatus is capable of simulating three phases of the gait cycle in a static mode, of assessing an isolated region of an AFO under study, and of testing the entire AFO freely. The orthosis test apparatus provides quantitative information that may be of value to orthotic education programs, research and development centers, the orthotics industry, and large central fabrication facilities in evaluating and quantifying mechanical behavior of AFO designs. Better understanding of AFO mechanical behavior can add to the array of evaluative criteria that the orthotist needs in providing the most assistive AFO design, including biomechanical support, functionality, and durability for their patients.

Assessment of the non-linear behaviour of plastic ankle foot orthoses by the finite element method

The stiffness characteristics of plastic ankle foot orthoses (AFOs) are studied through finite element modelling and stress analysis. Particular attention is given to the modelling and prediction of non-linear AFO behaviour, which has been frequently observed in previous experimental studies but not fully addressed analytically. Both large deformation effects and material non-linearity are included in the formulation and their individual influence on results assessed. The finite element program is subsequently applied to the simulation of a series of tests designed to investigate the relation between AFO trimline location and stiffness for moderate and large rotations. Through careful consideration and identification of key modelling parameters, the developed finite element solution proves to be a reliable and effective alternative means of assessing variations of a typical plastic AFO design so that particular patient requirements could be met, in the long term.

A Review of Thermoplastic Ankle-Foot Orthoses Adjustments/Replacements in Young Cerebral Palsy and Spina Bifida Patients

A retrospective study was performed to determine how long a thermoplastic ankle-foot orthosis (AFO) will fit appropriately and when subsequent adjustment and replacement are indicated. Clinical records of cerebral palsy and spina bifida patients ages birth to 21 years who used six types of thermoplastic AFOs from 1982 to 1992 were reviewed. Neuromusculoskeletal functional status appears to determine the AFO design prescribed and its replacement. Adjustments to thermoplastic AFOs primarily involve heat flaring to alter plastic contours and provide sufficient space for donning, doffing and pressure relief over regions of bony prominence. Further research is necessary to confirm the results obtained in this study.

ANKLE WEIGHT EFFECT ON GAIT: ORTHOTIC IMPLICATIONS

Oxygen consumption during ambulation was measured in 10 normal subjects wearing ankle weights of 0.91 kg, 1.82 kg, and 2.73 kg, either on the right ankle or bilaterally. Subjects walked at self-selected speeds and oxygen consumption was measured over 1-minute intervals during steady-state walking. Oxygen consumption per unit distance and oxygen consumption rate demonstrated significant positive linear correlations with added weight (P = .001, P = 0.007, respectively). Velocity demonstrated a significant decrease when correlated with added weight (P = 0.03). Multiple regression analysis was used to relate these measures of oxygen consumption rates to velocity, age, and added weight, yielding predictive relationships. Based on these results, the weight of orthoses should be minimized in order to maximize walking velocity and minimize oxygen consumption per unit distance. The advantage of a light-weight, molded plastic ankle-foot orthosis (AFO) over heavier AFO designs is demonstrated by this study.

A Calf Corset Weightbearing Ankle-Foot Orthosis Design

president of Tamarack Habilitation Technologies Inc., 1471 Energy Park Drive, St. Paul, MN 55108–5204. retired from Northeast Metro Technical College, St. Paul, MN. orthotist at Gillette Children's Hospital, 200 E. University Ave., St. Paul, MN 55101.

A Calf Corset Weightbearing Ankle-Foot Orthosis Design

president of Tamarack Habilitation Technologies Inc., 1471 Energy Park Drive, St. Paul, MN 55108–5204. retired from Northeast Metro Technical College, St. Paul, MN. orthotist at Gillette Children's Hospital, 200 E. University Ave., St. Paul, MN 55101.

A Calf Corset Weightbearing Ankle-Foot Orthosis Design

president of Tamarack Habilitation Technologies Inc., 1471 Energy Park Drive, St. Paul, MN 55108–5204. retired from Northeast Metro Technical College, St. Paul, MN. orthotist at Gillette Children's Hospital, 200 E. University Ave., St. Paul, MN 55101.

Characteristics of ankle-foot orthoses for management of the spastic lower limb.

A retrospective study was done on the effects of a change in the design of ankle-foot orthoses used in the treatment of 29 hemiplegic children. Nine of 13 children treated with plantarflexed ankle-foot orthoses required surgery, compared with only one of 16 with dorsiflexed ankle-foot orthoses. This difference is highly significant.