Presented at NACOB 98: North American Congress on Biomechanics Canadian Society for Biomechanics - American Society of Biomechanics University of Waterloo Waterloo, Ontario, Canada August 14-18, 1998

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THE INFLUENCE OF EXTERNAL ORTHOTIC SUPPORT ON ADAPTIVE GAIT CHARACTERISTICS

S. Spaulding¹, L. Livingston², H. Hartsell³

¹Faculty of Health Sciences, School of Occupational Therapy,
The University of Western Ontario , 1201 Western Road, London, ON N6G 1H1

²Faculty of Arts and Science, Department of Kinesiology and Physical Education,
Wilfrid Laurier University, 75 University Ave W, Waterloo, N2L 3C5

³Physical Therapy Graduate Program, College of Medicine, The University of Iowa,
2600 Steindler Building, Iowa City, IA 52242-1008

INTRODUCTION

Functional instability occurs in approximately 40% of patients after inversion sprain (Lentell et al., 1995). The factors associated with functional instability may result in movement difficulties during activity (Ryan, 1994). The purpose of this study was to evaluate effects of orthotic use on gait characteristics.

REVIEW AND THEORY

External support is provided to restrict undesirable ankle movement (Feuerbach and Grabiner, 1993) and to stabilize the ankle to prevent further injury (Karlsson et al., 1993). Bracing effectiveness has been tested during discrete movement skills (Greene and Wight, 1990) and by evaluating changes of passive soft tissue resistance (Hartsell and Spaulding, 1997), but has not been evaluated during locomotion.

PROCEDURES

The control group consisted of subjects with no history of lower extremity pathology( age = 27.3, s.d. =4 years). The chronic group consisted of subjects (age = 24.3, s.d. = 5 years) who had sustained two or more moderate ankle sprains that required medical intervention.

Subjects walked along a 30 metre walkway under three conditions; unbraced, flexible brace, and semi-rigid brace. The two braces were a flexible orthosis (Swed-O Universal; Swed-O, North Branch, MN 55056) and a semi-rigid orthosis (Sure- step; Joint Solutions Inc., Tustin, CA 92680). Subjects walked on a level surface, up an 18 cm step and up a ramp with a 5° incline.

Kinematic data were collected using an IRED data collection system (Optotrak, Canada). Ground reaction force data were collected using a force plate (AMTI, USA) placed flush with the walkway.

Discrete angular and linear kinematic variables at heel contact, toe off and as the foot passed over the edge of the altered surface were collected. Ground reaction forces and impulses were also collected to give an indication of preparation for a change in surface characteristics. Separate repeated measures ANOVA procedures were used to analyse the angular, linear, force and impulse data.

RESULTS

The mean ankle angle at foot contact was 15° dorsiflexion for the control group and for the chronic ankle sprainers was 6° plantarflexion. Ankle angles were significantly different between the two groups (F(1,10) =12.91, p<.005). At toe- off, the mean ankle angle was 3° dorsiflexion for the control group whereas for chronic ankle sprainers, the ankle angle was 30° dorsiflexion. The ankle angles were significantly different by group (F (1,6)=6.32, p<.046) but not by brace or condition.

Significant differences between conditions included push-off time (F(2,20)=9.82, p<.001), foot angular displacement at foot contact (F(2,12)=8.46, p<.005) and toe off (F(2,12)=5.75, p<.018), maximum F(2,20)=59.59, p<.001) and minimum (F(2,20)=27.59, p<.001) AP GRF measured at the ground. Foot absolute angle was greater during the ramp than level walking and was lower for the step condition (F(1,10)=21.81, p<.001) .

Interaction effects by group, brace and condition were noted for the braking force (F(4,40)=3.96, p<.008) (Figure 1), and foot angle at foot contact F(4,24)=4.86, p<.005) and toe off (F(1,6)=12.27, p<.01).

DISCUSSION

Greater variability was noted in gait characteristics among the members of the chronic group relative to the group with no previous injuries. This variability may reflect the heterogeneity of the injuries that individuals have suffered and the various levels of function (Bouffard, 1993). The variability may also reflect that a variety of protective gait adaptations may be implemented if an ankle is chronically unstable. Chronic ankle sprainers adapt their gait parameters differently than do individuals with healthy ankles, but these adaptations are not necessarily altered by the use of an orthotic device.

Differences that were noted included the ankle angle at all points of interest during the gait cycle. The ankles of the chronic sprainers were more plantarflexed during foot contact, regardless of brace used. A position closer to neutral would have provided the ankle joint with more stability, since most inversion sprains occur at between 20° and 30° of plantar flexion. However, the plantar flexed position of the ankle at foot contact may reflect compensatory positioning of the ankle.

Differences in gait characteristics to accommodate to changes in the environment have been reported previously (Patla et al, 1991). The step condition requires an abrupt change in the height, but the foot is landing on a flat surface. The ramp may encourage the individual to land with the ankle in increased plantarflexion, due to the position of the shank at foot contact. This position is one of increased instability for the talo-crural joint. Knee angles are increased to elevate the foot. The foot angle is higher during the step condition, suggesting that the toe is raised to avoid inadvertent contact. Increased braking impulse and peak force in braking in the step condition encourages the body to slow down to prepare for the next step. There were decreased horizontal and vertical propulsive impulses, that, together with the increased knee angle suggests that the step is cleared by changing knee angle.

Brace use did not produce a strong impact on gait characteristics. This information, coupled with the knowledge that braces are effective in providing external support (Hartsell and Spaulding, 1997), suggests that braces may be effective for protection without impeding normal overground locomotion.

REFERENCES

Bouffard, M. (1993). Adapt. Phys. Activity Quarterly, 10, 371-391.

Feuerbach, J.W., and Grabiner, M.D. (1993). JOSPT 7, (3): 149-154

Greene, T.A. and Wight, C.R. (1990). JOSPT. 11, (10): 453-466.

Hartsell, H.D. and Spaulding, S.J. (1997). Foot and Ankle International, 18, 144-150.

Karlsson, et al. (1993). Sports Med.,16: 210-215

Lentell, G. et al.(1995). JOSPT, 21:206- 215.

Patla, A.E., et al. (1991). J of Exp.Psych: Human Perception and Performance. 17,3,603-634.

Ryan, L. (1994). Aust. J. of Phys., 40: 41- 47.