Improvement of postural stability considers a primary goal in post-stroke rehabilitation, and training of weight-bearing symmetry remains the main exercise during the recovery process. The improved postural stability is a result of restored symmetrical weight distribution which has a beneficial impact on patient health. Eventually, health care specialists make the emphasis on the subject to implement this practice regarding its benefits and efficiency.
Maintaining undisturbed postural upright stance has been a significant disorder challenging various stroke patients. According Ribeiro et al. (2018), the ability to maintain an upright postural stance in stroke patients is mostly characterised by uneven distribution of body weight, where the non-paretic limbs bear a significantly higher body mass, which causes a postural sway. Arguably, this postural asymmetry is attributed to the most preferred posture though in some instance, various researchers have discovered some compelling evidence linking the issue to other subjective factors (Hendrickson et al. 2014). Over the years, researchers have sought to understand the primary factors associated with the postural imbalance stance in stroke patients. However, the paradigms of assessing the weight distribution amongst these stroke patients have created a significant interest since various research experts have raised issues on validity, reliability, and justification of the study designs, as well as sample size adopted by various investigators. Therefore, according to the available literature, it is imperative to explore the causative factors attributed to the weight bearing asymmetry of the lower-limbs in stroke patients, which results to the stance in the upright posture of the victims (Genthon et al. 2008). In this regard, this review seeks to comprehend different scholars approach to the weight asymmetry issue in stroke patients and also explore their conclusive findings, recommendations, as well as the study limitations to discover the existing research gap in this field of concern.
Recent research studies revealed a significant relationship between weight-bearing asymmetry (WBA) and postural stability in patients with stroke. Weight-bearing asymmetry is one of the patterns characterising standing posture of patients with hemiparetic gait. Different modes of a standing position of hemiparetic patients include considerable postural sway, an asymmetrical contribution of lower limbs to balance control, and increased visual dependency to control balance. For instance, on assessing 27 readily available patients with chronic stroke using a cross-sectional design from rehabilitation clinics, Sheikh et al. (2017) realized that the average value of WBA index significantly reduced after using a shoe lift (p<0.05). However, the variation of the mean value of other postural control characteristics was not statistically significant at 0.05 alpha level (p>0.05). Contrary to previous research studies, findings of their research surmised that there was no significant association between decreased weight bearing asymmetry and improved postural control during a prolonged standing period in stroke patients.
Furthermore, Karthikbabu et al. (2016) conducted a cross-sectional study using 112 participants in tertiary care rehabilitation centres to assess whether there was any association between pelvic alignment and weight-bearing asymmetry (WBA) in chronic stroke survivors dwelling in a community. The results of the study revealed that there was a significantly stronger correlation between lateral pelvic tilt with weight-bearing asymmetry (r=0.63, p<0.0001) than anterior pelvic tilt (r=0.44, p<0.0001). The result of this study concurred with Sheikh’s (2017) findings, which indicated that pelvic tilt toward the affected side instance significantly reduces the average value of WBA index in chronic stroke patients.
Moreover, according to Mansfield et al. (2011), a cross-sectional assessment of twenty healthy controls and 33 persons with single stroke using non-matched case-control study design, substantiated the claim that deduced between-limb temporal synchronisation was associated with increased postural stability in the mediolateral direction and enhanced weight-bearing asymmetry in stroke individuals. The researchers further investigated that controlling for quiet standing, stroke individuals have decreased temporal synchronisation of a centre of pressure changes under the feet compared to the control group individuals. Nevertheless, the study results could not lead to a valid conclusion since the clinical significance of the identified relationship could be determined. Besides, the finding of this study could not be generalised to other population since the control and case groups were not identical regarding other characteristics. Therefore, the causative effects could be attributed to the confounding factors. The recent research studies have consistently reported that individuals experiencing weight-bearing asymmetry condition have more weight borne on the less affected side since the more-affected lower limb has reduced to the contribution to the standing balance control (Nicolas et al., 2008). In their study, Mansfield et al. (2012) proposed that between-limb synchronisation and weight-bearing symmetry, the overall postural sway measures distinctly reveal specific control problems, which are essential estimates of still stance control for post-stroke. In authenticating their claim, the researchers conducted a retrospective study using 100 individuals with stroke admitted to inpatient rehabilitation. They revealed that controlling for other measures of standing balance control, postural sway and stance load symmetry, temporal synchronisation was significantly associated with motor impairment and prospective falls. Nonetheless, the findings were not considered supportive to the Mansfield’s et al. (2012) deductions since they investigated that temporal synchronisation for standing balance seemed to be a unique and important index of balance control, while controlling for other measures. Similarly, De Haart et al. (2004) conducted an exploratory cohort study with healthy elderly persons as the reference values for the study findings to increase the strength for causality and enhance generalisability investigation with less potential recall bias. In this study, all the 39 in patients with a mean age of 61.6 years admitted in the rehabilitation centre were eligible, although two were lost to follow-up remaining with only 37 participants were followed up from November 1998 to November 2000. The results of this study showed that there was excessive postural sway and instability on stroke patients compared to the reference group of elderly persons. It was also identified that weight-bearing asymmetry, the most revealed in patients with disturbed sensibility, reduced significantly during the first four weeks, but after that continued to be exasperated by attentional disturbance (p=0.001). Based on their finding, they concluded that balance recuperation in post-acute stroke inpatients is associated by a reduction in postural sway and instability as well as by a decrement in visual dependency. Therefore, it suggested balance recovery and stance must be significantly associated with other mechanisms other than the restoration of support and balance of the paretic leg. Most researchers argue that stance is controlled using weight-bearing asymmetry and the restoration of postural symmetry is the aim of physiotherapeutic treatments. Conversely, other researches postulate that weight-bearing asymmetry may not be an essential target of rehabilitating stability after stroke. Kiyota et al. (2011) argued that although previous studies had revealed a significant relationship between the degree of functional impairment in stroke patients and stance symmetry, these studies did not disclose how patients develop an asymmetric standing posture just after stroke. Therefore, Kiyota et al. (2011) designed a study that aimed at examining the first stage of adaptive changes of stance control in patients with hemiparesis condition. The study included nine hemiparesis patients aged 48 to 62 years and 6 to 19 days after stroke.
Besides, from the findings, it was established that weight-bearing asymmetry might be associated with improving increased body sway and muscular over-activity of the non-paretic leg. However, these findings could not be used to generalise the results to a higher population or bring a general conclusion due to the presence of threats of internal and external validity. Besides, the survey employed a poor research design that could lead to inaccurate results. More so, Adegoke et al. (2012) asserts that further studies have investigated the weight-bearing asymmetry among hemiparetic stroke survivors as well as the association between percentage weight bearing asymmetry (PWBA) and functional ambulation performance, which was assessed using the Emory Functional Ambulation Profile (E-FAP). Adegoke et al. (2012) employed 53 stroke survivors with hemiparesis where 35 individuals were male and 18 were female aged between 40 to 86 years of age (mean=58.87; SD=9.21 years). The researchers used an E-FAP as an instrument for data collection due to its high construct and concurrent validity, inter-rater reliability, and test-retest reliability.
Based on the study findings, there was a statistically significant positive correlation (r=0.675, p<0.0001) between PWBA and total E-FAP scores of participants, which indicated that PWBA could be used to investigate functional ambulation recovery in stroke survivors. Mansfield et al. (2013) corroborated their study assumptions as well as implicit claims by other researchers through an exploratory longitudinal study for the prevalence and clinical determinants of stance asymmetry and the association between gait asymmetry and postural control among stroke patients. The study recruited 147 individuals for six months where 59 were symmetric healthy, 18 were suffering from paretic asymmetry (PA), and 70 had non-paretic asymmetry (NPA). From the results, it was established that subjects with PA depended less on the loaded limb for control than the subject with NPA.
Besides, PA subjects were found to rely more on visual information for postural control than symmetric individuals. However, individuals between the PA and NPA groups were found to be insignificantly different. These findings supported some of the previous study finding that paretic limb loading was not associated with instability. Overall, the review of different research articles indicated that most of the previous research studies revealed a significant association between weight-bearing asymmetry and unstable stance in stroke patients. These findings demonstrated that most of the stroke patients tend to put more weight on the non-paretic leg than the affected side, thus causing postural imbalance in their stance. Besides, some of the researchers acknowledged that physical exercises rehabilitation centres, where the patient is trained to move around quickly from one point to another, helps in postural control recovery. However, it was realized that most of the reviewed studies attested to have had limitations regarding threats to both internal and external validity, which could have led to biased inferences or conclusive evidence. Similarly, some of the studies sample size and research designs were not statistically viable, thus a raising a significant question in the generalisability of the findings.
Therefore, this backdrop indicates a knowledge gap in that the researchers need to address the findings issue by design a more rigorous study focusing not only on the sample adequacy but also on the viable research design to enhance valid conclusion. Furthermore, an appropriate design will rule out effects of confounding factors as well as threats to internal and external validity of the findings.
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