Northwestern University Feinberg School of Medicine

Northwestern University Prosthetics-Orthotics Center

An Investigation of Ankle Joints for Ankle Foot Orthoses (AFOs)

Principal Investigator: Steven Gard, PhD

Co-Investigators: Andrew Hansen, PhD, and Rebecca Stine, MS

Stefania Fatone, PhD, Project Director

Funded by: Veterans Administration Merit Review

Status: Completed

Purpose

When pathologies such as hemiplegia are present, ankle-foot function is disrupted and an AFO may be worn to restore function. The function imparted by AFOs relies largely upon the degree of resistance provided to rotation about the ankle. There are a number of ankle joints and motion control devices currently available for use in thermoplastic AFOs, but functional evaluation of orthotic ankle components is limited. The purpose of this randomized cross-over study was to assess the effect of different ankle components on the gait of adults with post-stroke hemiplegia who wore articulated AFOs.

MethodCustom molded articulated AFOs with full-length foot-plates.

Three articulated AFOs with full-length foot-plates were custom molded of 3/16" polypropylene from the same cast by a single orthotist (a heel height board was used to cast the ankle at 90°). (See figure.) Subjects wore each AFO for 2 weeks in random order: 90° plantarflexion stop/free dorsiflexion (AFO1); plantarflexion limiter/free dorsiflexion (AFO2); 90° plantarflexion stop/dorsiflexion assist (AFO3). All AFOs used Tamarack Flexure Joints (Becker Orthopedic, Troy, MI). A baseline shoes only condition (NoAFO) was also recorded using standardized footwear (New Balance #926). Durometer selection for the motion limiter (60, 70 or 90) and dorsiflexion assist joints (75 or 85) were based on clinical evaluation of participants.

Gait analyses were conducted using the Helen Hayes marker set with ankle markers secured to the AFO with the proximal joint screw so that the marker center was in line with the joint axis. The VA Chicago Motion Analysis Research Laboratory is equipped with an 8-camera digital real-time motion capture system (MAC, Santa Rosa, CA) and 6 force plates (AMTI, Watertown, MA) embedded in a 10m level walkway. OrthoTrak software (MAC) was used to calculate kinematic, kinetic and temporospatial data. A minimum of 3 trials were averaged for each subject walking at a normal freely selected speed. Non-parametric statistical analyses were conducted.

Results

Data were analyzed for 21 subjects, 9 males and 12 females (mean age: 54.0 ± 7.7 years, mean mass: 81.7±18.8kg, mean height: 169.3±10.5cm). Mean time since stroke was 6.6±5.8 years (12 left, 9 right hemiplegia). Subjects were broken down into two groups depending on whether or not knee hyperextension was present during gait without an AFO. Temporospatial variables did not differ between groups, but peak knee moment during loading response was significantly different for all conditions; knee angle during loading response were significantly different for all but the AFO2 and AFO3 conditions; and ankle angle at mid swing and initial contact was significantly different for all but the AFO2 conditions. There was no difference between conditions with regards to the load transfer transient. Table 1 shows the results as median (interquartile range) for all subjects and for the group with knee hyperextension.

Conclusions

For all subjects, all AFO conditions significantly increased walking speed and step length on the involved side to the same extent compared to NoAFO. In general, all AFOs had a more substantial effect on gait in persons with hemiplegia who exhibited knee hyperextension when walking without an AFO. Dorsiflexion assist joints did not provide additional dorsiflexion during swing when compared to AFOs without dorsiflexion assist. Results suggest that a larger sample size is needed to detect post-hoc differences for peak knee angle during loading response and load transfer transients.

Related Publications/Presentations

Fatone S, Stine R, Gard S. Randomized Cross-over Study of AFO Ankle Components in Adults with Post-Stroke Hemiplegia. Paper presented at: 13th ISPO World Congress; May 10-15, 2010; Leipzig, Germany.

Fatone S, Stine R, Gard S. Randomized cross-over study of AFO ankle components in adults with post-stroke hemiplegia. Paper presented at: Annual Meeting and Scientific Symposium of the American Academy of Orthotists and Prosthetists; February 24-27, 2010; Chicago, IL. (Recipient of the Thranhardt Award).

Fatone S, Gard S, Stine R. Randomized cross-over study of AFO ankle components in adults with post-stroke hemiparesis: preliminary results. Annual Summer Technical Meeting of the Midwest Chapter of the American Academy of Orthotists and Prosthetists. Lake Geneva, WI, 2009.

Fatone S, Gard S, Stine R. Randomized cross-over study of AFO ankle components in adults with post-stroke hemiparesis: preliminary results. Paper presented at: Proceedings of the American Academy of Orthotists and Prosthetists Annual Meeting; March 4-7, 2009; Atlanta, GA.