An Investigation of Foot Alignment and Support in
Ankle Foot Orthoses (AFOs)

Steven Gard, PhD and Dudley Childress, PhD, Principal Investigators
Stefania Fatone, PhD, Project Director

Co-Investigators:
Andrew Hansen, PhD and Rebecca Stine, MS, Northwestern University
Bryan Malas, CO, MHPE, Department of Orthotics, Children's Memorial Hospital

Funded by: Veterans Administration Office of Research and Development (R&D), Rehabilitation R&D Service, Merit Review Grant A2676I

Purpose

Changes in the angular attitude of the tibia and the foot plate length of an Ankle Foot Orthosis (see figure on right) may alter the moments occurring at the knee during walking. The purpose of this study was to investigate the effect on gait of AFO ankle alignment and foot-plate length in people with hemiplegia following stroke.

Method

Sixteen participants with post-stroke hemiplegia underwent three gait analyses, each two weeks apart walking on: (1) a standard-aligned (ankle at 90°), thermoplastic, articulated AFO with 90° plantarflexion stop and full-length foot-plate; (2) the same AFO re-aligned so that the tibia was perpendicular to the ground; and (3) the same AFO (tibia perpendicular to ground) with ¾ length foot-plate. A No AFO baseline condition was also recorded. Standardized footwear ensured heel height was constant for all conditions. The gait of 12 able-bodied subjects was measured for on a single occasion. Bilateral kinematics and kinetics of the pelvis and lower limbs were acquired along with in-shoe plantar pressure data.

To compare plantar pressure data for the two AFOs with full-length foot-plate (AFOs 1 and 2), the foot was divided into three equal regions:  hind, mid- and fore-foot. Mean pressure (MP), peak pressure (PP), contact time (CT) and the pressure-time integral (PTI) in each region for each condition were analyzed based on the mean of the middle four steps per trial averaged over three trials while walking at a normal freely-selected speed. To compare plantar pressure data between the AFOs with full and ¾ length-foot plate (AFOs 2 and 3), ink foot prints were used to identify eight regions:  the heel, navicular, metatarsal heads 1 to 5 and hallux regions. Mean pressure, peak pressure, contact time and the pressure-time integral (PTI) in each region for each condition were analyzed based on the mean of the middle four steps of each trial averaged over three trials while walking at a normal freely-selected speed.

Results

In adults with hemiplegia, walking speed was unaffected by the different conditions. Compared to the no AFO condition, all AFOs significantly decreased plantar flexion at initial contact and mid-swing and significantly changed the peak knee moment in early stance from flexor to extensor (see figure below). Both AFOs with full-length foot-plates significantly increased the peak stance phase plantar flexor moment compared to No AFO and resulted in a peak knee extensor moment in early stance that was significantly greater than able-bodied subjects, while the AFO with ¾ length foot-plate resulted in dorsiflexion during stance and swing that was significantly less than able-bodied subjects. COP excursion was significantly increased in all three AFO conditions compared to No AFO. Compared to control subjects, excursion of the COP was significantly less only for the No AFO condition.

Improved ankle-foot kinematics resulted in a more biomimetic rollover shape (ROS). ROS is the effective geometry to which the ankle-foot complex conforms between initial contact (IC) and contralateral IC. An effective ROS during gait may facilitate forward progression. For the involved limb, the standard-aligned AFO significantly increased the ROS arc length (from 32.6% to 55.7% of foot length [FL]) and arc radius (67.4% to 139.3% of FL) and significantly altered the sagittal plane location of the first center of pressure (COP) point, moving it posterior to the ankle center (–1.2% to –20% of FL) (p < 0.002 for all comparisons). However, when hemiplegic patients walked with an AFO, their mean arc radius was greater, mean arc length less, and the first COP point further posterior than those of control subjects. At present, some limitations exist to modeling the ROS of subjects with hemiplegia as the lower arc of a circle since some of the data from hemiplegic subjects cannot be adequately represented by this model (e.g., some of the ROS are concave-down or are flat). Additional investigation is required to see if we can further improve ROS by altering AFO design and allow users to further increase step length and walking speed.

Results of plantar pressure analysis suggested that changes in AFO alignment of about 5-7 degrees did not appear to have a substantial impact on plantar pressure within an AFO in subjects with post-stroke hemiplegia when data were analyzed based on hind, mid- and fore-foot regions. When AFOs with different foot-plate lengths were compared, pressure data did not appear to be substantially influenced by changes in AFO foot-plate length, but the timing of pressure beneath different regions of the foot changed. The AFO with ¾ length foot-plate appeared to have a more normal sequence of contact times.

The results of this study suggest that articulated AFOs with plantar flexion stops improve ankle alignment and roll-over shape during gait in persons with post-stroke hemiplegia and that a full-length foot-plate in conjunction with a plantar flexion stop may be considered to improve early stance knee moments for individuals with post-stroke hemiplegia. The AFO conditions tested in this study did not alter plantar pressure distribution substantially in persons with post-stroke hemiplegia.

Related Publications

Fatone, S. (2008) Functional Evaluation of Ankle Foot Orthoses in Adults with Post-Stroke Hemiplegia.  Invited Speaker, Current Clinical Concepts in Orthotic & Prosthetic Rehabilitation, sponsored by the VHA O&P Education Committee as an extension of the O&P Strategic Planning, VA Prosthetic and Clinical Logistics (Central Office), February 6-8, Long Beach, CA.

Fatone, S., Hansen, A. (2007) Effect of an Ankle Foot Orthosis on Roll-over Shape in Adults with Hemiplegia following Stroke.  Invited Speaker, 16th Annual Visiting Professor Symposium, Motion Analysis Center, Children’s Memorial Hospital, November 9, Chicago, IL.

Fatone, S. (2007) Effect of Ankle Foot Orthosis Alignment and Foot-Plate Length on the Gait of Adults with Hemiplegia.  Invited Speaker, American Academy of Orthotists and Prosthetists Midwest Chapter Fall Meeting, November 3, Hickory Hills, IL.
 
Fatone, S. (2007) Functional Evaluation of Ankle Foot Orthoses in Adults with Post-Stroke Hemiplegia.  Invited Speaker, Bio-Interest Group (BIG) seminar series, Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, October 15, Urbana-Champaign, IL.

Fatone, S., Gard, S. and Malas, B. (2007) Effect of AFO Alignment on Plantar Pressures During Walking in Adults With Hemiplegia.  12th World Congress of the International Society for Prosthetics and Orthotics, July 29 to August 30, Vancouver, BC, Canada.

Fatone, S., Gard ,S. and Malas, B. (2007) Effect of Ankle Foot Orthosis (AFO) foot plate length on plantar pressures in adults with hemiplegia.  Annual Meeting and Scientific Symposium of the American Academy of Orthotists and Prosthetists, March 21-24, San Francisco, California.

Fatone, S. and Hansen, A. (2006) Effect of Ankle Foot Orthosis on Roll-over Shape in People with Hemiplegia.  Annual Meeting and Scientific Symposium of the American Academy of Orthotists and Prosthetists, March 1-4, Chicago, Illinois. (Recipient, Howard R. Thranhardt Lecture Award).

Fatone, S, Hansen, AH, Gard, SA and Malas, BS. (2005) Effects on Gait of Ankle Alignment and Foot-Plate Length in Ankle Foot Orthoses (AFOs). American Academy of Orthotists and Prosthetists, Annual Meeting, March 16-19, Orlando, Florida.

Fatone, S. (2005) AFO study draws to a close: An investigation of the effect on gait of ankle alignment and foot-plate length. Capabilities, 13(1):6-12. Northwestern University, Chicago, IL, USA.

Fatone, S. (2004) Effects on Gait of Ankle Alignment and Foot-Plate Length in Ankle Foot Orthoses. Guest Speaker, American Prosthetics and Orthotics Inc. Fall Scientific Meeting, October 23, Des Moines, Iowa.

Fatone, S, Hansen, AH, Gard, SA and Malas, BS. (2004) The Effect of Ankle Foot Orthosis Alignment on the Knee During Gait in Post-Stroke Hemiplegia. International Society for Prosthetics and Orthotics, 11th World Congress, August 1-6, Wanchai, Hong Kong, China.

Fatone, S, Hansen, AH, Gard, SA and Malas, BS. (2004) An Investigation of Alignment and Support in Ankle Foot Orthoses (AFOs). Invited Speaker, American Academy of Orthotists and Prosthetists, Midwest Chapter Spring Meeting, June 3-5, Milwaukee, Wisconsin, USA.

Fatone, S, Gard, SA, Childress, DS and Malas, B. (2004) An Investigation of Foot Alignment and Support in Ankle Foot Orthoses (AFOs). Gait and Clinical Movement Analysis Society, 9th Annual Meeting, April 21-24, Lexington, Kentucky, USA.

Fatone, S, Gard, SA, Childress, DS and Malas, B. (2003) An Investigation of Foot Alignment and Support in Ankle Foot Orthoses (AFOs). Children’s Memorial Hospital Visiting Professor Symposium, November 7, Chicago, Illinois, USA.

Fatone, S, Gard, SA, Childress, DS and Malas, B. (2003) An Investigation of Foot Alignment and Support in Ankle Foot Orthoses (AFOs). American Congress of Rehabilitation Medicine, October 23-26, Tucson, Arizona, USA. Archives of Physical Medicine and Rehabilitation, 84(10):A1-A12. and Neurorehabilitation and Neural Repair, 17(4).

Fatone, S. (2003) Research Projects Place New Emphasis on Orthotics. Capabilities, 11(4):12-13. Northwestern University, Chicago, IL, USA.

Fatone, S, Gard, SA, Childress, DS and Malas, BS. (2002) An Investigation of Foot Alignment and Support in Ankle Foot Orthoses (AFOs). Third VA Rehabilitation Research and Development National Meeting, February 10-12, Arlington, Virginia, USA (poster).

Fatone, S, Malas, B and Gard, S. (2001) NUPRL & RERP Launches New Orthotic Research. Capabilities, 10(4):1-3,9,11. Northwestern University, Chicago, IL, USA.