Hemiplegic Gait Foot Orthosis
Biomechanical analysis of hemiplegic gait with and without an Ankle Foot Orthosis
Introduction
Stroke is the leading cause of adult disability and according to the American Heart Association approximately 400/100, 000 persons over the age of 45 years has a first stroke each year in the United States. To regain independence in mobility is therefore one of the primary goals for rehabilitation after stroke.
Characteristics of Hemiplegic gait
Other factors that might influence the level of limitation in walking activity are learning ability, coping skills, motivation, medical co-morbidities, physical endurance levels, family support, housing and the amount and type of rehabilitation training (Perry 1992). In addition, several features of post-stroke hemiplegic gait are commonly observed, including slow and asymmetric steps with poor selective motor control, prolonged stance duration on the non-paretic side, increased double support time relative to neurologically healthy individuals walking at self-selected speeds, delayed and disrupted equilibrium reactions and reduced weight bearing on the paretic limb(Roth and Harvey 1996).
Further, smooth and symmetric forward progression of the body is impaired with a large variation in gait patterns related to the degree of recovery (Roth et al. 1997). Moreover, well-controlled intra-limb and inter-limb coordination is replaced by mass limb movement patterns (synergies) on the paretic side requiring compensatory adjustments of the pelvis and non-paretic side. Consequently, compensatory movements necessary for ambulation produce abnormal displacement of the centre of gravity, resulting in increased energy expenditure (Cirstea and Levin 2000).
Stroke studies have reported altered kinematic and kinetic gait profile in both magnitude (peak and valley angle, moment and power), and pattern (shape and direction of curves), indicating an impaired ability to generate and grade the forces that control limb movement (Yavuzer G. 2001). Their findings did not show a relationship between gait pattern and walking velocity and did not support the goal of normalisation of movement patterns in management of stroke patients.
As well as problems with moving and controlling limbs, many hemiplegic patients experience difficulty in maintaining balance, because a defect in the “body image” causes them to ignore the affected side. They suffer from severe postural instability and postural asymmetry during quiet standing in the frontal and sagittal planes (de Haart et al. 2004).They present an asymmetrical pattern of lateral movements and greater excursions of the pelvis (excessive excursion of the centre of gravity) than healthy subjects walking at similar speeds (Bujanda et al. 2003).Moreover, the accelerations are asymmetrical, with the highest values occurring when weight bearing is on the paretic side.
This suggests difficulties in controlling the lateral motion of the trunk segment, which might be very important for maintaining balance in locomotor activities. Impaired balance is often related to uneven weight bearing, and increased energy expenditure and may be associated with laterally directed falls and a high risk of fractures in these patients (Kanis et al. 2001). The mass flexion pattern then causes synergistic contraction of the hip flexors, knee flexors, and ankle dorsiflexors during the swing phase (Chen et al. 2003). This primitive motor control produces the primitive patterned limb movement and inhibits normal progression during walking.
The goal of a stroke rehabilitation programme is to regain the ability to function and return to a productive and satisfying life. Rehabilitation can achieve these goals by either restoring body functions, or compensating for any body dysfunction, or by combining of both (Platz 2004). Walking ability is one of the most important functions for the reason that independent ambulation is essential for community reintegration and social participation.
Accordingly, gait training accounts for a large proportion of time spent in stroke rehabilitation. Any limitation in an activity may be due to impairments in different body functions, restoration of normal movements of the trunk, pelvis, and lower extremity while walking, improving symmetry and weight bearing on the paretic side, and establishing an energy-efficient walk are the most important goals of gait training in stroke patients. Therefore, if normal ambulatory function could not be regained, various orthosis and aids are prescribed for substitution and compensation.
Hemiplegic gait with and without an Ankle Foot Orthosis
An ankle foot orthosis is commonly used to provide optimal ambulation in patients with hemiplegia by preventing excessive plantarflexion that is one cause of toe walking. Several AFO designs are available for hemiplegic patients. An AFO is used to ensure toe clearance and prevent excessive inversion of the ankle joint during the swing phase of gait, absorb the body-weight impact at the initial stance, and support forward propulsion of the body during the mid- to late stance phase. These functions are mainly achieved by controlling the magnitude of the assist moment of an AFO in the sagittal plane. Inversion of the ankle joint can be prevented through appropriate control of plantarflexion because inversion is always accompanied by plantarflexion.
that AFOs have positive effects on hemiplegic gait parameters, increasing cadence, walking speed, single and double step length, ankle dorsiflexion angle at heel strike and swing (Gok et al. 2003). While walking speed, and cadence, step length usually decrease in hemiplegic gait pattern (Lehmann et al. 1987) ,the study revealed an increase in walking speed particularly with the metallic AFO. Walking speed with the metallic AFO was (0.41 ± 0.16 versus 0.37 ± 0.14 with the plastic AFO and 0.32 ± 0.13 without an AFO P <0.05).
Further, hemiplegic patients usually have less dorsiflexion during heel contact and mid-swing due to loss of motor control, spasticity of the gastrocnemius- soleus group, and ankle contracture. The study found that both AFOs limited the excessive plantarflexion, forming a potential for dynamic knee instability. Similarly ,it is has been suggested that the greater the plantarflexion resistance of an AFO, the greater the external bending moment at the knee (Lehmann et al. 1983).On the other hand , the lack of forward movement of the centre of pressure on the ankle produces a markedly increased knee flexion moment in midstance when body weight is supported by the paralysed limb (Lehmann et al. 1985).
The effects of an ankle-foot orthosis on spatiotemporal parameters and energy cost of hemiplegic gait was evaluated by Franceschini et al (2003). Their study recruited chronic hemiplegic patients, with the same gait pattern alteration. It has been reported that AFOs can improve an abnormal base of support and limb instability during the stance phase and improve the limb clearance and limb advancement during the swing phase (Esquenazi and Hirai 1991), and Franceschini et al (2003) study found that the orthosis significantly improved self-selected speed (15.47 versus 21.39 m/min), stride cycle (2.33 versus 2.08 s), stance (1.83 versus 1.48 s) and double support (1.55 versus 1.16 s), and reduced energy cost (0.76 versus 0.49 ml O2/kg/m) of walking without affecting cardiorespiratory response.
Moreover, a significant correlation was found between the improvement of double support and the reduction of energy cost (Franceschini et al. 2003). Similarly Danielsson and Sunnerhagen (2004) measured walking speed and energy cost in stroke patients with and without a carbon composite ankle foot orthosis. The authors found that use of a carbon composite ankle foot orthosis in patients with stroke increase speed and decrease energy cost during walking (Danielsson and Sunnerhagen 2004).
and symmetry ratios of some gait parameters also improved, such as stance duration (2.0+1.5 s with an AFO versus 3.3 +3.6 s without an AFO) and deceleration forces (1.6+0.5 with an AFO versus 1.9+0.6 without an AFO) during gait. The improvement in some gait symmetry parameters, indicating a more balanced gait when wearing an AFO in patients with hemiparesis (Pohl and Mehrholz 2006).
Lehmann et al. (1987) measured gait kinetics and kinematics in seven hemiplegic and seven able-bodied adults. The study compared their gait patterns at similar speeds and assessed the effectiveness of an ankle-foot orthoses, which were double-stopped in 5 degrees of dorsiflexion or 5 degrees of plantarflexion. Walking speed, gait events and knee moments were significantly improved by using an AFO. While the walking speed of hemiplegic subjects improved significantly(p<0.05) by using an AFO in 5 degrees of dorsiflexion as compared to the speed achieved without an AFO or an AFO in 5 degrees of plantarflexion, the walking speed was slower than that of able-bodied subjects (8-55m/min vs. 49-79m/min respectively).
Further, there was also a significant difference in the heel strike phase of subjects using a 5 degrees dorsiflexed AFO as compared to without an AFO and an AFO in 5 degrees of plantarflexion. The use of the an AFO in 5 degrees of dorsiflexion and an AFO in 5 degrees of plantarflexion showed a significant difference in the midstance phase when compared to those subjects without an orthosis. The push off phase was found longer in the plantarflexed AFO but the difference was not significant.
However, there was a significant difference in the mean total knee flexion moment of the hemiplegic subjects ambulating with an AFO .The mean total knee flexion moment during the midstance phase with the dorsiflexed AFO was greater than the moment seen without or with the plantarflexed AFO. The study found that dorsiflexion stop created a bending moment and the plantar flexion stop created an extensor moment at the knee in hemiparetic patients (Lehmann et al. 1987).
Churchill et al (2003) examined the relative effects of footwear and an ankle-foot orthosis on hemiplegic gait. Patients were evaluated without footwear, with their footwear alone and with an AFO.
Gait data were collected using the RIVCAM system, a two-dimensional kinematic recording system. The result showed a significant increase in the stride length variable. The AFO improved a patient’s stride by approximately 5 cm in contrast to walking with footwear alone. However, swing times did not vary over the three conditions and the result for velocity showed no statistically significant effects (p = 0.069). Moreover, the results for cycle time, cadence and stance were all statistically not significant (Churchill et al. 2003).
Yokoyama et al. (2005) considered the kinematic effects on hemiplegic gait of a newly designed ankle-foot orthosis with oil damper resistance. The oil damper generates a resistive moment to the plantarflexion rotation of the ankle joint at the initial stance phase and the magnitude of the plantarflexion resistive moment at the heel strike can be adjusted to accommodate each patient’s condition by turning an adjustment screw. Their study compared the gait of 2 hemiplegic patients while they were wearing either an AFO with the oil damper or an AFO with the plantarflexion stop.
The study found that no functionally significant changes were observed in the time-distance factors, and there was sufficient plantarflexion of the ankle and mild flexion of the knee during initial stance phase when they wore the AFO with the oil damper and authors concluded that the AFO with the oil damper achieved sufficient plantarflexion of the ankle and mild flexion of the knee by adjusting a proper plantarflexion resistive moment during initial stance phase in patients with hemiplegia (Yokoyama et al. 2005).
Iwata et al. (2003) evaluated the effect of an inhibitor bar attached to an ankle-foot orthosis in hemiplegic stroke patients with tonic toe flexion reflex (TTFR).the results indicated that the maximal speed increased by 13.8%, in the TTFR group as a result of increased stride length and cadence , and the difference was significant (P=.0045).The inhibitor bar also increased stride length by 8.0%, from 70.3±20.2cm to 76.0±23.2cm, in the TTFR group (P=.0398); the increase in the control group was 0.7% (from 71.6±11.6cm to 72.0±11.9cm).
Cadence significantly increased by 6.1% in the TTFR group (P=.0056); the values before and after an inhibitor bar attachment were 82.6±23.2 steps/min and 86.9±22.0 steps/min, respectively. The increase in the rate in the control group was 0.4%, from 70.2±28.2 steps/min to 70.5±28.2 steps/min. The inhibitor bar may provide additional mechanical support and stability to the foot during the stance phase. This increased stability may, in turn, allow greater excursion of the non–weight-bearing limb and helped to improve walking ability in hemiplegic patients who have TTFR (Iwata et al. 2003).
Therefore, patients wearing anAFO cleared their toes better during swing and pivoted overthe stationary foot better. The corresponding changes of theankle angles were characterized by less plantar flexion duringthe swing and a larger dorsiflexionduring the stance phase (Hesse et al. 1999). Rao et al. (2006) evaluated the beneficial effect of ankle-foot orthoses on gait pattern in subjects with stroke. The results found that using an AFO improved velocity, cadence, and step length in subjects with stroke.
The mean velocities without and with an AFO were 49.1 and 57.3 respectively (P<.001); the mean cadence without and with an AFO was 67.9 and 74.4, respectively (P<.001); the mean step-length difference without and with an AFO was 11.3 and 9.0, respectively (P<.05). Stance phase percentage of the gait cycle was significantly shorter on the orthotic side than the sound side (F=39.8, P<.001) (Rao et al. 2006).
Conclusion
An ankle-foot orthosis is frequently prescribed in the rehabilitation of hemiplegic patients suffering from an equinovarus deformity. It should assist foot clearance during the swing phase, improve the mode of initial contact, prevent ankle inversion injuries, and help in advancing the body during midstance. It has been found that orthoses can limit kinesiological problems of the foot–ankle complex and improve the spatiotemporal parameters (Burdett et al. 1988). Therefore, with an AFO hemiplegic patients walk faster, with a longer stride, diminished plantar flexion, and larger active ankle moment.
Moreover, orthoses could lower the energy cost of walking (Corcoran et al. 1970). Although, an ankle-foot orthosis offers some biomechanical benefits, the disadvantages still remain. It has been reported that immobilization of the ankle joint without peripheral nerve lesion leads to diminish the motor cortex area of the inactivated tibial anterior muscle compared to the unaffected leg without changes in spinal excitability or motor threshold. Further, the area reduction was correlated to the duration of immobilization (Liepert et al. 1995).Accordingly, clinicians should consider the advantages as well as the disadvantages of an ankle-foot orthosis prior to prescribe this intervention to hemiplegic patients.
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