How Does Ankle-foot Orthosis Stiffness Affect Gait in Patients With Lower Limb Salvage?

Abstract

Background Ankle-foot orthoses (AFOs) are commonly prescribed during rehabilitation after limb salvage. AFO stiffness is selected to help mitigate gait deficiencies. A new custom dynamic AFO, the Intrepid Dynamic Exoskeletal Orthosis (IDEO), is available to injured service members but prescription guidelines are limited. Questions/purposes In this study we ask (1) does dynamic AFO stiffness affect gait parameters such as joint angles, moments, and powers; and (2) can a given dynamic AFO stiffness normalize gait mechanics to noninjured control subjects? Methods Thirteen patients with lower limb salvage (ankle arthrodesis, neuropathy, foot/ankle reconstruction, etc) after major lower extremity trauma and 13 control subjects who had no lower extremity trauma and wore no orthosis underwent gait analysis at a standardized speed. Patients wore their custom IDEO with posterior struts of three different stiffnesses: nominal (clinically prescribed stiffness), compliant (20% less stiff), and stiff (20% stiffer). Joint angles, moments, powers, and ground reaction forces were compared across the varying stiffnesses of the orthoses tested and between the patient and control groups. Results An increase in AFO compliance resulted in 20% to 26% less knee flexion relative to the nominal (p = 0.003) and stiff (p = 0.001) conditions, respectively. Ankle range of motion and power generation were, on average, 56% (p \ 0.001) and 63% (p \ 0.001), respectively, less than controls as a result of the relatively fixed ankle position. Conclusions Patients with limb salvage readily adapted to different dynamic AFO stiffnesses and demonstrated few Support was provided by

Stiffness modification of two ankle‐foot orthosis types to optimize gait in individuals with non‐spastic calf muscle weakness – a proof‐of‐concept study

“…At the knee, the minimum knee angle (extension) during stance changed little across stiffness conditions, which agrees with earlier reports [19, 30, 31]. Possibly, the knee extends once a sufficient stiffness is reached.…”

The effect of changing plantarflexion resistive moment of an articulated ankle–foot orthosis on ankle and knee joint angles and moments while walking in patients post stroke

“…Findings from the studies using non-articulated AFOs may not be directly applicable to articulated AFOs. Some studies suggested that the effect of non-articulated AFO’s resistive moment on overall walking performance might be minimal in patients with ankle muscle weakness due to various limb salvage procedures (Harper et al, 2014; Russell Esposito et al, 2014). However, the resistive moment of a non-articulated AFO is generally adjusted by trimming its material or exchanging its component.…”

Investigation of the ankle foot orthoses footplates stiffness

“…3, b) but is still quite similar for all the AFOs. The further reduction of the distance between fixture and loading points leads to rapid growth of stiffness and its scatter (6,(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)3 and 28,4-57,6 N/mm for forces F3 and F4 on scheme Fig. 3, b correspondingly).…”

“…(not to mention universal models). Various researches of children and adult patients gait proved that AFO's efficiency mostly depends on its stiffness (or rigidity), what is usually evaluated based on the energy cost [5][6][7][8] or walking performance [9][10][11][12]. The same approach is also used when developing exoskeletons [13,14].…”