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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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Previous research has shown that in quiet stance people who have suffered a stroke take more weight on their unaffected leg than on their hemiplegic leg (Dickstein et al 1984, Sackley 1990). However, it is unclear whether or not this asymmetrical weight bearing is present throughout the time that the individual is standing up from the seated position or if it just exists at the end of the movement. In addition, although many investigators have analysed the kinematics of sit-to-stand in healthy adults (e.g. Shenkman et al 1990), this has not been investigated in stroke patients. In the present study we looked at these two aspects of the sit-to-stand movement performed by people who have had a stroke, i.e., we investigated symmetry of weight bearing and we analysed lower limb joint angles during this movement. It was hypothesised that the stroke participants would take less weight on their affected leg, and more on their unaffected leg, compared to the controls. Additionally, it was speculated that in comparison to the healthy adults the stroke patients would not transfer their weight as far forward over their base of support and that their lower limbs would be less extended at the completion of the movement.
Ten patients with right-sided hemiplegia and ten healthy age-matched adults participated in this study. All participants were between the ages of 40 and 81, had no significant lower limb orthopaedic problems and were able to stand up independently without using their upper limbs. Two AMTI force plates were used to record the vertical forces exerted by each lower limb as the participants stood up from the seated position. All force plate signals were normalised to body weight. The peak force produced by each leg and the forces exerted at 25 and 75% of movement time were recorded (movement time was calculated from initial hip flexion to the time at which full extension of the hip was first reached). In addition, the correlation between the force signals recorded from each lower limb was calculated. This measure was used in order to investigate the overall degree of symmetry of weight bearing as the participants stood up.
Movement kinematics were recorded using the OPTOTRAK system. Start angle, end angle, maximum flexion angle and time to maximum flexion angle were calculated for the hip, knee and ankle. For the pelvis start angle, maximum anterior tilt and time to maximum anterior tilt were calculated. Between 2-5 trials of sit-to-stand performed by each participant were analysed and an ANOVA was used to compare the stroke patients to the controls using a significance level of p<0.05.
At both 25 and 75% of movement time the stroke participants carried significantly less weight on their hemiplegic leg, and more weight on their left leg, compared to the controls. The peak force exerted by the stroke participants was also less than the controls for the right leg and greater for the left leg (see Figure 1 for right leg forces). The correlation between the force signals recorded from the two legs was significantly higher for the healthy adults (0.9263) than for the stroke patients (0.8130). These results extend the findings of previous work on symmetry of weight bearing in stroke. They demonstrate that people who have suffered a stroke take significantly more weight on their unaffected leg throughout the sit-to-stand movement and not just during quiet stance.
Figure 1: Peak right leg force and the force exerted by this leg at 25 and 75% of movement time.
Both groups of participants demonstrated similar values of maximum hip and knee flexion and ankle dorsiflexion. Although the time to reach maximum hip flexion and ankle dorsiflexion was significantly longer for the stroke participants, when these times were analysed as a percentage of movement time there were no differences between the two groups. This shows that the increase in times to reach maximum angles at the hip and ankle were proportional to the increase in movement time demonstrated by the stroke participants (which was 3103 msec compared to 2384 msec for the controls). On the other hand, for the pelvis there were several differences between the stroke patients and the controls. The stroke participants showed a greater posterior pelvic tilt at the start of movement and their maximum anterior tilt was less than that produced by the control participants; both of these differences were significant (see Table 1). In addition, both real time and percentage of movement time to maximum anterior tilt were longer for the stroke patients. This difference was significant for real time (p=0.0034) and close to significant for percentage of movement time (p=0.0648).
These results show that the stroke patients' ability to transfer their weight forward over their feet was impaired at the level of the pelvis but not at the hip and ankle. It is possible that no differences existed between the two groups with respect to the hip and ankle because all stroke participants had enough motor recovery to enable them to stand up independently without using their upper limbs. In order to do so they must have been able to transfer a sufficient amount of their weight over their base of support.
| Variable | Stroke | Control | p value |
|---|---|---|---|
| End hip A | 172° | 182° | 0.0344 |
| End ankle A | 117° | 111° | 0.0443 |
| Start pelvic A | -33° | -22° | 0.0227 |
| Max pelvic A | 6° | 20° | 0.0176 |
Table 1: Angle magnitudes that showed a significant effect of group. A- angle. Note: for the ankle values of > 90( indicate plantar flexion and for the pelvis negative values indicate posterior tilt and positive values anterior tilt.
Hip, knee and ankle angles at the commencement of movement did not show a significant difference between the two groups of participants whereas end hip and ankle (but not knee) angles did. At the end of movement the stroke participants exhibited less hip extension and more plantar flexion than the controls (see Table 1). In summary, as speculated, as the stroke patients stood up from the seated position they took less weight on their affected leg and more on their unaffected leg and they did not extend their trunk over their lower limbs as much as the healthy adults. However, the hypothesis that the stroke participants would not transfer their weight as far forward over their base of support as the controls was only supported at the pelvis and not at the hip or ankle.
Dickstein R, Nissan M, Pillar T, Scheer D, Foot-ground pressure pattern of standing in hemiplegic patients. Physical Therapy, 64, 1, 19-23.
Sackley CM, The relationship between weight-bearing asymmetry after stroke, motor function and activities of daily living. Physio Theory and Practice, 6, 179-185.
Shenkman M, Berger R, Riley PO, Mann R & Hodge WA (1990). Whole-body movement during rising to standing from sitting. Physical Therapy, 70, 10, 638-651.
We would like to express our gratitude to Linda Kalbfleisch and Pia Amping for their help with data collection and processing and to Kim Helm and the other physiotherapists who recruited participants for this study.
