Design principles, manufacturing and evaluation techniques of custom dynamic ankle‐foot orthoses: a review study

Abstract

Ankle-Foot Orthoses (AFO) can be prescribed to allow drop-foot patients to restore a quasi-normal gait pattern. Standard off-the-shelf AFOs are cost-effective solutions to treat most patients with foot and ankle weakness, but these devices have several limitations, especially in terms of comfort. Therefore, custom AFOs are increasingly adopted to address drop-foot when standard solutions are not adequate. While the solid ones are the most common type of AFO, providing full stability and strong resistance to ankle plantarflexion, passive dynamic AFOs (PD-AFOs) represent the ideal solution for patients with less severe ankle weakness. PD-AFOs have a flexible calf shell, which can bend during the stance phase of walking and absorb energy that can be released to support the limb in the push-off phase. The aim of this review is to assess the state-of-the-art and identify the current limitations of PD-AFOs. An extensive literature review was performed in Google Scholar to identify all studies on custom PD-AFOs. Only those papers reporting on custom PD-AFOs were included in the review. Non peer-reviewed papers, abstract shorter than three pages, lecture notes and thesis dissertations were excluded from the analysis. Particular attention was given to the customization principles and the mechanical and functional tests. For each topic, the main results from all relevant papers are reported and summarized herein. There were 75 papers that corresponded to the search criteria. These were grouped according to the following macro-topics: 16 focusing on scanning technologies and geometry acquisition; 14 on customization criteria; 19 on production techniques; 16 on mechanical testing, and 33 on functional testing. According to the present review, design and production of custom PD-AFOs are becoming increasingly feasible due to advancements in 3D scanning techniques and additive manufacturing. In general, custom PD-AFOs were shown to provide better comfort and improved spatio-temporal parameters with respect to standard solutions. However, no customization principle to adapt PD-AFO stiffness to the patient’s degree of ankle impairment or mechanical/functional demand has thus far been proposed.

Materials and Manufacturing for Ankle–Foot Orthoses: A Review

“…Drop foot is particularly serious during the swing phase of walking, causing toe strikes instead of heel strikes and, as a result, leading to increased risks of stumbling and falling. [28,29] As a result of this problem, patients with drop foot find it difficult to release the pedals while driving and have trouble walking in sandals and slippers, which frequently come off. [30] Depending on the primary reason for the drop foot, this gait disorder may be either temporary or permanent.…”

“…The flexibility in the active AFO is given by either a deformable shell (nonarticulated) or a hinge joint (articulated). [ 28 ] While active AFOs require more complex systems than passive orthoses, they can nonetheless offer greater gait stability and improved independence. [ 29 ] In many cases, the articulation of an active AFO (i.e., flexion and extension movements) is actively assisted by the actuators.…”

“…Although standard off‐the‐shelf AFOs are cheaper, they come with a number of drawbacks: 1) they are available only in certain sizes (e.g., small, medium, and large); 2) they do not always fit the patient's ankle and foot geometry, which can make them less comfortable than a custom‐made AFO; and 3) due to their fixed mechanical characteristics, they are unable to handle the unique functional demands or disabilities of patients. [ 28 ] Although the styles and materials of prefabricated orthoses are influenced by market demands, manufacturers are usually reluctant to change materials and designs. If the material or design of a prefabricated orthosis is no longer in demand, it is simply discontinued.…”

Differential Diagnosis of “Foot Drop”: Implications for Peripheral Nerve Surgery

“…Such patients are rendered to a lifetime of relying on an ankle-foot orthosis (AFO) for walking and nighttime to prevent an equinovarus contracture. 2,3 Without the dynamic movement of the foot and ankle, running and high-impact activities are generally not a reality. Contrary to popular belief, foot drop can be caused by more than just insult to the common peroneal nerve at the fibular head (fibular tunnel).…”

“…Such patients are rendered to a lifetime of relying on an ankle–foot orthosis (AFO) for walking and nighttime to prevent an equinovarus contracture. 2 3 Without the dynamic movement of the foot and ankle, running and high-impact activities are generally not a reality.…”