Multi-segment foot mobility in a hinged ankle-foot orthosis: the effect of rotation axis position

Comparison between Helical Axis and SARA Approaches for the Estimation of Functional Joint Axes on Multi-Body Modeling Data

Functional methods usually allow for a flexible and accurate representation of joint kinematics and are increasingly implemented both for clinical and biomechanics research purposes. This paper presents a quantitative comparison between two widely adopted methods for functional axis estimation, that is, the helical axis theory and the symmetrical axis of rotation approach (SARA). To this purpose, a multi-body model was developed to simulate the lower limb of a subject. This model was designed to reproduce different motion patterns, that is, by selecting the active degrees of freedom of the simulated ankle joint. Thanks to virtual markers attached to each segment, the multi-body model was used to generate simulated motion capture data that were then analyzed by instantaneous helical axes and SARA algorithms. To achieve a synthetic representation of joint kinematics, a mean helical axis and an average SARA functional axis were estimated, along with dispersion parameters and rms distance data that were used to quantitatively assess the performance of each method. The sensitivity of each algorithm to different combinations of range and speed of motion, scattering of marker clusters, sampling rate, and additive noise on markers’ trajectories, was finally evaluated.

The comparison of the effect of innovative designed storing-restoring hybrid passive AFO versus posterior leaf spring AFO on ankle joint kinematic in drop foot patients: A case series using a single subject design

Background: Drop foot syndrome is a disorder characterized by foot slapping after the initial contact and foot-dragging during the swing phase. Passive and hybrid passive ankle foot orthoses (AFOs) are often prescribed in these patients; however, the effects of these AFO designs on kinematic parameters during gait are unclear. The aim of this study was to compare the effect of innovative designed storing-restoring hybrid passive AFOs versus posterior leaf spring AFO on ankle joint kinematics in drop foot patients.

Methods: The present study was a case series where a single case and 3 cases with drop foot syndrome were recruited. This study was designed in 2 phases: the baseline phase with their PLS AFOs and an intervention phase in which innovative designed AFO were assessed. Each phase included 5 measurement sessions which were performed in 5 consecutive weeks. The celeration line method was used to detect the significant differences between the phases.

Results: The results of this study showed a significant increase in the kinematic angles parameters at the initial contact, the loading response, the mid stance, terminal stance, pre swing, initial swing, mid swing, and terminal swing with the innovative designed AFO than with PLS AFO (p<0.05).

Conclusion: The results of the present study suggested that use of the innovative designed AFO may have a positive effect on ankle joint kinematics parameters in people with drop foot.

A methodology for the customization of hinged ankle-foot orthoses based on in vivo helical axis calculation with 3D printed rigid shells

This study aims to develop techniques for ankle joint kinematics analysis using motion capture based on stereophotogrammetry. The scope is to design marker attachments on the skin for a most reliable identification of the instantaneous helical axis, to be targeted for the fabrication of customized hinged ankle-foot orthoses. These attachments should limit the effects of the experimental artifacts, in particular the soft-tissue motion artifact, which affect largely the accuracy of any in vivo ankle kinematics analysis. Motion analyses were carried out on two healthy subjects wearing customized rigid shells that were designed through 3D scans of the subjects' lower limbs and fabricated by additive manufacturing. Starting from stereophotogrammetry data collected during walking and dorsi-plantarflexion motor tasks, the instantaneous and mean helical axes of ankle joint were calculated. The customized shells matched accurately the anatomy of the subjects and allowed for the definition of rigid marker clusters that improved the accuracy of in vivo kinematic analyses. The proposed methodology was able to differentiate between subjects and between the motor tasks analyzed. The observed position and dispersion of the axes were consistent with those reported in the literature. This methodology represents an effective tool for supporting the customization of hinged ankle-foot orthoses or other devices interacting with human joints functionality.

Multisegment Foot Models and Clinical Application After Foot and Ankle Trauma: A Review

Since the end of the 1990s, several multisegment foot models (MSFMs) have been developed. Several models were used to describe foot and ankle kinematics in patients with foot and ankle pathologies; however, the diagnostic value for clinical practice of these models is not known. This review searched in the literature for studies describing kinematics in patients after foot and ankle trauma using an MSFM. The diagnostic value of the MSFMs in patients after foot and ankle trauma was also investigated. A search was performed on the databases PubMed/MEDLINE, Embase, and Cochrane Library. To investigate the diagnostic value of MSFMs in patients after foot and ankle trauma, studies were classified and analyzed following the diagnostic research questions formulated by Knottnerus and Buntinx. This review was based on 7 articles. All studies were published between 2010 and 2015. Five studies were retrospective studies, and 2 used an intervention. Three studies described foot and ankle kinematics in patients after fractures. Four studies described foot and ankle kinematics in patients after ankle sprain. In all included studies, altered foot and ankle kinematics were found compared with healthy subjects. No results on patient outcome using MSFMs and costs were found. Seven studies were found reporting foot and ankle kinematics in patients after foot and ankle trauma using an MSFM. Results show altered kinematics compared with healthy subjects, which cannot be seen by other diagnostic tests and add valuable data to the present literature; therefore, MSFMs seem to be promising diagnostic tools for evaluating foot and ankle kinematics. More research is needed to find the additional value for MSFMs regarding patient outcome and costs.

Ankle-foot orthosis bending axis influences running mechanics

Passive-dynamic ankle-foot orthoses (AFOs) are commonly prescribed to improve locomotion for people with lower limb musculoskeletal weakness. The clinical prescription and design process are typically qualitative and based on observational assessment and experience. Prior work examining the effect of AFO design characteristics generally excludes higher impact activities such as running, providing clinicians and researchers limited information to guide the development of objective prescription guidelines. The proximal location of the bending axis may directly influence energy storage and return and resulting running mechanics. The purpose of this study was to determine if the location of an AFO's bending axis influences running mechanics. Marker and force data were recorded as 12 participants with lower extremity weakness ran overground while wearing a passive-dynamic AFO with posterior struts manufactured with central (middle) and off-centered (high and low) bending axes. Lower extremity joint angles, moments, powers, and ground reaction forces were calculated and compared between limbs and across bending axis conditions. Bending axis produced relatively small but significant changes. Ankle range of motion increased as the bending axis shifted distally (p<0.003). Peak ankle power absorption was greater in the low axis than high (p=0.013), and peak power generation was greater in the low condition than middle or high conditions (p<0.009). Half of the participants preferred the middle bending axis, four preferred low and two preferred high. Overall, if greater ankle range of motion is tolerated, a low bending axis provides power and propulsive benefits during running, although individual preference and physical ability should also be considered.

The influence of passive-dynamic ankle-foot orthosis bending axis location on gait performance in individuals with lower-limb impairments

BACKGROUND

Passive-dynamic ankle-foot orthoses are commonly prescribed to augment impaired ankle muscle function, however their design and prescription are largely qualitative. One design includes a footplate and cuff, and flexible strut connecting the two. During gait, deflection occurs along the strut, with the greatest deflection at a central bending axis. The vertical location of the axis can affect lower extremity biomechanics. The goal of this study was to investigate the influence of bending axis location on gait performance.

METHODS

For thirteen participants with unilateral ankle muscle weakness, an additive manufacturing framework was used to fabricate passive-dynamic ankle-foot orthosis struts with central and off-center bending axes. Participants walked overground while electromyographic, kinetic and kinematic data were collected for three different bending axes: proximal (high), central (middle) and distal (low), and the participants indicated their order of bending axis preference after testing. Gait measures and preference effect sizes were examined during six regions of the gait cycle.

FINDINGS

A few differences between bending axes were observed: in the first double-leg support peak plantarflexion angle, peak dorsiflexion moment and positive hip work, in the early single-leg support peak knee extension moment and positive ankle and knee work, and in the late single-leg support gastrocnemius activity and vertical ground reaction force impulse. In addition, preference was strongly related to various gait measures.

INTERPRETATION

Despite the observed statistical differences, altering bending axis location did not produce large and consistent changes in gait performance. Thus, individual preference and comfort may be more important factors guiding prescription.