Lower Limb Proprioception in Low Back Pain and Its Relationship With Voluntary Postural Control

Abstract

This study aimed to investigate whether patients with low back pain (LBP) had impaired lower limb proprioception and its association with somatosensory acuity. Thirty patients with LBP and 30 asymptomatic people volunteered, using Sway Discrimination Apparatus tests to assess somatosensory acuity during voluntary anteroposterior and mediolateral postural sway. Results showed significantly reduced somatosensory acuity in mediolateral sway in LBP patients (p = 0.005) with ankle, knee, and hip proprioception showing significantly impairment compared to asymptomatic controls (all p ≤ 0.012). Regression analysis showed that ankle and hip proprioception were significantly associated with somatosensory perception (0.001 ≤ p ≤ 0.026, 0.067 ≤ R²≤ 0.235). Overall, findings suggested a global deterioration of lower limb proprioception in LBP patients, with ankle and hip proprioception playing crucial role in somatosensory perception.

Keywords:

• low back pain
• ankle
• proprioception
• postural control
• somatosensory perception

INTRODUCTION

Postural control is a necessary activity that contributes to various mobility tasks in daily life, such as posture transfers and stair negotiation (Clemson et al., 2012). Accurate and efficient dynamic postural control ability is critically linked to elite sports performance, as it facilitates the necessary trunk stability and effective feedforward support for limb movements in postural control tasks (Akbaş et al., 2021). Evidence also suggests that good postural control ability is important to reduce the risk of sports injuries as it is associated with rapid response to potential injury situations and correction of unstable posture in sports (Dallinga et al., 2012). For people with musculoskeletal disorders, increased pain severity and disability are associated with decreased postural control reflected by delayed muscle onset (Yu et al., 2021) and dynamic postural instability (Sun et al., 2023), and postural control training has been found to contribute to the realignment of the biomechanical structure of the spine (Bayattork et al., 2020) and lower limb stability (Benis et al., 2016).

Postural control ability depends on both the sensitivity of somatosensory receptors and sensory integration in the central nervous system (Chiba et al., 2016). Since the onset of human upright walking, the reduction of the base of support has posed significant challenges to human postural control. According to motor learning theory (Muratori et al., 2013), there is a sense of posture that comes from the body to help individuals maintain balance during voluntary activities. The sense of posture, namely somatosensory perception, is the integration of visual, vestibular, and proprioceptive afferences (Goble et al., 2019; Peterka, 2002), where the contribution of proprioceptive signals to somatosensory perception is predominant in postural control tasks (Horak, 2006). Specifically, the lower limbs are the only body part that contacts the ground during the postural control task of maintaining a standing position, and lower limb proprioception correspondingly becomes a vital source of somatosensory perception (Goodworth et al., 2014). Some studies have shown that hip proprioception may be related to performance in voluntary postural control tasks such as gait (Qu et al., 2022) and dynamic stability maintenance (Wingert et al., 2014). There has been shown to be a significant positive correlation between proprioception of the ankle and knee joints and static postural stability (Song et al., 2021) and sports achievement (Rein et al., 2011).

Low back pain (LBP) is a leading cause of disability and is considered a major epidemic that constitutes a challenge affecting economic and social development (GBD 2021 Low Back Pain Collaborators, 2023). The prevalence of LBP varies among different ages and regions, with the prevalence gradually decreasing from 8.2% to 7.5% in the past three decades (Wu et al., 2020). A recent study found that 4.2% of young adults aged 24–39 suffered from chronic LBP (Meucci et al., 2015). For patients with LBP, the influence of persistent pain on somatosensory perception is bidirectional. On the one hand, noxious stimulation in the low back region is associated with deficits in the proprioceptive receptors in spinal structures, such as intervertebral disks and paraspinal muscles, which alter the position sense and motion sense of the lumbar spine (Holm et al., 2002; Meier et al., 2019). Systematic reviews have shown that patients with LBP demonstrate increased error in the lumbar spine position reproduction test compared to the healthy controls (Ghamkhar & Kahlaee, 2019; Korakakis et al., 2021; Tong et al., 2017). On the other hand, pain can disrupt the integration of somatosensory perception (Nijs et al., 2024). When altered somatosensory signals are transmitted through the spinal cord to the somatosensory cortex, there may be a generalized decrease in somatosensory acuity due to cortical reorganization (Murray & Sessle, 2024; Nijs et al., 2024). In order to adapt to the altered somatosensory acuity, patients with LBP may respond by increasing trunk and lower muscle stiffness to reduce postural sway while standing (Fitzcharles et al., 2021; Koch & Hänsel, 2019).

Stiffness is a significant predictor of musculoskeletal disorders and disability (Thakral et al., 2014). The stiffness strategy is a common postural control approach in patients with LBP used to mitigate spinal pain by increasing muscle tone (Meier et al., 2019; van Dieën et al., 2019). Adopting a stiffness strategy in patients with LBP may involve an active limitation on interaction with somatosensory perception, as general decreases in somatosensory acuity can influence the accuracy and efficiency of postural control (Meier et al., 2019; Stanton et al., 2017). Given that proprioceptive signals from the lower limbs are crucial sources of integration output for somatosensory perception during postural control in the upright position, lower limb proprioception may inevitably be affected as well (Xiao et al., 2022). However, there is a lack of observational studies on the effect of LBP on lower limb proprioception and its relationship with somatosensory perception. Therefore, it is crucial to investigate the changes in lower limb proprioception in patients with LBP, as it may elucidate the impact of pain on whole-body postural control.

With regard to the methodology of assessing somatosensory perception, Han et al. (2016) proposed that ecologically valid test postures and analysis using the psychophysical method can optimally reflect the sensitivity of somatosensory receptors and the integration function of the central nervous system. Chen et al. (2019) developed and validated a psychophysics-based technology, the Sway Discrimination Apparatus (SwayDA), to quantify the somatosensory acuity in voluntary postural sway (Chen et al., 2019). In the SwayDA tests, somatosensory acuity was reflected by the accuracy with which participants can distinguish between different voluntary postural sway amplitudes. Similarly, a series of Active Movement Extent Discrimination Apparatus (AMEDA) were designed for assessing proprioception. The application of AMEDA in multi-joint proprioception assessment has been well-developed (Waddington et al., 1999), including for the neck (Lee et al., 2005), shoulder (Hams et al., 2019), knee (Chang et al., 2022), and hip (Cameron et al., 2008). In AMEDA testing, the ability to accurately distinguish between members of a set of self-initiated movement extents is an indicator of proprioceptive acuity. In terms of ecological validity, the AMEDA tests require participants to distinguish between different active movement extents that relate to activities of daily living while in a standing position, without loss of general (but not target) visual input (Han et al., 2016). For example, the ankle AMEDA targets inversion and eversion because lateral sprain is the main pattern of ankle injury (Gribble et al., 2016), and the design of the knee and hip AMEDA test considers the lunge and leg swing as common functional action modes in daily life and sports.

Despite the bidirectional effect of pain, there is little evidence to indicate whether the proprioceptive acuity of the lower limbs is affected by LBP. If LBP does have a significant effect on lower limb proprioception, the extent to which these changes contribute to somatosensory sensitivity in voluntary postural control tasks remains unknown. Therefore, the primary aim of this study was to investigate the changes in ankle, knee, and hip proprioceptive acuity in patients with LBP. In the event of finding impairments in lower limb proprioception, this study further aimed to explore the association between lower limb proprioception scores and changes in somatosensory acuity observed during voluntary postural sway. The hypothesis proposed was that individuals with LBP will exhibit decreased proprioceptive acuity in ankle, knee, and hip proprioceptive acuity. Additionally, it is hypothesized that lower limb proprioception serves as the primary source of somatosensory perception in voluntary postural control tasks.

MATERIAL AND METHODS

Design

This study was a cross-sectional design measuring somatosensory perception in voluntary postural sway, lower limb proprioception, and mobility in both patient groups with LBP and who were asymptomatic of LBP. This study was conducted in a laboratory setting from August 2022 to March 2023.

Sample Size Estimation

Gpower 3.1 for Windows (Universität Düsseldorf, Düsseldorf, Germany) was used to estimate the sample size of this study, via independent t test with an alpha level of 0.05, a power of 0.8, and an effect size of 0.71 for ankle proprioceptive acuity selected from a similar study (Xiao et al., 2022). Given the 10% dropout rate, the estimated sample size should be at least 58 participants.

Participants

Sixty participants were recruited from advertisements placed on social media. This comprised of 30 patients with LBP and 30 age and sex-matched asymptomatic controls. Those participants with self-reported nonspecific pain over 4 wk in the region between the 12th thoracic vertebra to the 1st sacrum were recruited into the LBP group (Knezevic et al., 2021). Asymptomatic controls were defined as people who were pain-free in their lower back and legs in the preceding 6 months. However, participants were excluded if they: (1) had a major injury in lower limbs or spine in the preceding 6 months, such as ankle sprain (Doherty et al., 2014); (2) were diagnosed with neurological or musculoskeletal diseases that may influence balance, such as Parkinson’s disease (Konczak et al., 2009); (3) were taking medications that may affect balance, such as antidepressants, or antihypertensive drugs (de Groot et al., 2013). This study was approved by the Swinburne University of Technology Ethics Committee with approval number 20225788-11032. Signed informed consent was obtained from the participants before the start of the trials.

Apparatus

SwayDA

The SwayDA (Figure 1) is a purpose-built device with good reliability and validity for quantitatively measuring somatosensory acuity during voluntary postural sway in patients with LBP (Chen et al., 2023). In the SwayDA tests, somatosensory acuity was reflected by the ability to distinguish between a series of voluntary sway extents in the sagittal plane or coronal plane. The full protocol has been published in Chen et al. (2023). Briefly, participants were instructed to stand on the testing platform with both feet aligned with the ischial tuberosity before the SwayDA tests. When the SwayDA tests commenced, participants were asked to differentiate different voluntary sway extents. Due to the varying roles of somatosensation in different postural sway directions (Kanakis et al., 2014), the somatosensory acuity in three directions: anteroposterior sway (SwayDA-AP test), mediolateral sway to the dominant side (SwayDA-ML-D test), and non-dominant side (SwayDA-ML-ND test) were evaluated among the participants.

FIGURE 1. The Sway Discrimination Apparatus tests (a) anterior–posterior sway; (b) medial–lateral sway.

AMEDA

For proprioception testing, a series of AMEDA were employed in this study at three body sites: the ankle (Shi et al., 2023), knee (Chang et al., 2022), and hip (Cameron et al., 2008) (Figure 2). The reliability of the AMEDA for the lower limb has been established in previous studies, with the intraclass correlation coefficient ranging from 0.61 to 0.89 (Han et al., 2017; Waddington & Adams, 2004; Witchalls et al., 2014). Higher scores in the series of AMEDA tests represented better lower limb proprioception.

FIGURE 2. (a) & (b) Active Movement Extent Discrimination Apparatus (AMEDA) for the ankle; (c) & (d) AMEDA for the knee; (e) & (f) AMEDA for the hip.

As shown in Figure 2(a) and (b), the AMEDA-Ankle test required participants to distinguish between different self-initiated inversion angles of the ankle joint. The AMEDA-Ankle test apparatus consisted of a testing platform with handrails placed beside it to provide stability (Shi et al., 2023). At the center of the platform, there is a wooden board designed to rotate downwards by 10°, 12°, 14°, and 16° around the central axis. During the test, participants were asked to stand on the platform with one foot placed on the wooden board, aligned with its central axis. Before the AMEDA-Ankle test began, participants underwent a practice session to familiarize themselves with the four pre-set angles of ankle inversion (10°, 12°, 14°, and 16°). During the actual AMEDA-Ankle test, participants were instructed to voluntarily invert their ankles to swing the wooden board to the target positions and distinguish between the different inversion angles.

The AMEDA-Knee (Figure 2(c) and (d)) comprises a standing platform and an adjustable wooden disk (Chang et al., 2022). During the AMEDA-Knee test, participants were required to stand 10 cm away from the wooden disk, with the height of the disk adjusted to be parallel to the center of the patella. The distance between the disk and the patella was randomly set to 11, 12, 13, or 14 cm. Participants were then instructed to perform a forward lunge squat until their patella touched the wooden disk and distinguish between the four different forward squatting distances.

As can be seen in Figure 2(e) and (f), the AMEDA-Hip is composed of a horizontal bar (start bar) attached to one side of the main platform and a movable disk attached to the other side (Cameron et al., 2008). The start bar is positioned 20 cm above the platform surface. Additionally, the main platform features a 10 cm wide and 5 cm deep groove in the middle, which facilitates hip flexion and extension. During the AMEDA-Hip test, the starting position involves standing on one foot while facing the horizontal bar and lifting the other foot upward and forward to touch the start bar with the instep. Subsequently, participants were instructed to swing the leg backward until the heel touched the movable disk. They were then asked to return to their starting position and provide an absolute judgment on the extent of the swing. The test included four pre-set swing extents of 11, 12, 13, or 14 cm for participants to distinguish between.

Outcome Measures

Questionnaires

Waterloo Footedness Questionnaires were used to find the participants’ dominant side (Yang et al., 2018). For those who reported LBP, a numeric rating scale (Chiarotto et al., 2019) was used to quantify the severity of pain at the moment, and the total score of the Oswestry disability index (Chiarotto et al., 2016) was used to measure the degree of disability in daily life.

Procedure

Basic information and footedness of the participants were collected upon enrollment in this study. Prior to data collection, patients with LBP were asked to report the severity of pain and complete the Oswestry Disability Index questionnaire. Subsequently, somatosensory acuity and lower limb proprioception data were collected from all the included participants. The test sequence was randomized to avoid any potential learning effects. To prevent fatigue during the tests, participants were required to sit down for 1 min between different tests.

Data Analysis

In the SwayDA or AMEDA tests, “stimuli” refer to the target position that requires the participant to actively move, while “responses” denote the participant’s judgment of that target position. The raw data (stimuli and responses) from the SwayDA tests and AMEDA tests were processed by nonparametric signal detection theory (Roger et al., 2012), where the correct response was recognized as true-positive while the incorrect response was false-positive. The accumulated responses were then analyzed by pair-wise receiver operating characteristic curves, and the area under the curve (AUC) scores were calculated to reflect the sensory acuity in the SwayDA tests and AMEDA tests, with higher scores representing better acuity. In the AMEDA tests, the average scores of the dominant and non-dominant sides were then used for statistical analysis.

Statistical Analysis

Statistical analysis was performed using SPSS (Version 29 for Mac, IBM Corp, New York). The quantitative data were presented as mean ± SD. Independent t-tests were utilized to assess between-group differences, while Pearson’s correlation was employed to evaluate the association between somatosensory acuity and proprioceptive acuity in the ankle, knee, and hip. To further explore the relationship between somatosensory acuity and lower limb proprioception, linear regression analysis was conducted. The results of the SwayDA test served as the dependent variable, and the lower limb proprioception variables that showed significant correlations with the SwayDA test were used as independent variables. The statistical significance level was set at 0.05 for all analyses.

RESULTS

Demographic Information

The demographic information was expressed in mean ± SD. Thirty patients with LBP (age 19.5 ± 1.4 years, height 169.0 ± 7.3 cm, weight 66.7 ± 14.4 kg, n_female = 20) and 30 age-matched asymptomatic controls (age 18.9 ± 1.0 years, height 167.3 ± 8.9 cm, weight 61.1 ± 11.1 kg, n_female = 21) volunteered in this study. The severity of pain in the LBP group ranged from 3 to 5 (3.3 ± 0.6) with a duration of pain of 27.6 ± 15.2 months and 9.2 ± 3.2 scores in the Oswestry disability index. No significant differences were found in the demographic measures between the two groups (t_Age = −1.863, p = 0.067, Cohen’s d = 0.418; t_Height = −0.828, p = 0.411, Cohen’s d = 0.214; t_Weight = 1.690, p = 0.096, Cohen’s d = 0.436).

Differences in Lower Limb Proprioception and Somatosensory Acuity between Groups

The results of the SwayDA tests and AMEDA tests are shown in Table 1 and Figure 3. In the SwayDA-ML-D test, the LBP group showed impaired somatosensory acuity compared to the control group (t = −2.947, p = 0.005, Cohen’s d = −0.761). Although there were no significant differences in the SwayDA-AP test (t = −1.457, p = .150), Cohen’s d was −0.376 between the LBP group and control group. There was a significant global decrease in proprioception of ankle, knee, and hip (t_Ankle = −2.922, p = 0.005, Cohen’s d = −0.754; t_Knee = −3.504, p = 0.001, Cohen’s d = −0.906; t_Hip = −2.580, p = 0.012, Cohen’s d = −0.667) in the LBP group than in the control group.

FIGURE 3. The comparison of somatosensory acuity and lower limb proprioception between the low back pain group and the control group. LBP, low back pain; SwayDA-AP, Sway Discrimination Apparatus test – anterior–posterior sway; SwayDA-ML-D: Sway Discrimination Apparatus test – medial–lateral sway to the dominant side; SwayDA-ML-ND: Sway Discrimination Apparatus test – medial–lateral sway to the non-dominant side. *Significant difference between the low back pain group and control group. **Area under the curve: higher area under the curve scores representing better acuity.

TABLE 1. The mean AUC scores (SDs) for somatosensory acuity and lower limb proprioception between the low back pain group and the control group.

	LBP group	Control group	t	df	p	Cohen’s d
SwayDA-AP	0.684 ± 0.090	0.712 ± 0.055	−1.457	58	0.150	−0.376
SwayDA-ML-D*	0.620 ± 0.059	0.661 ± 0.047	−2.947	58	0.005	−0.761
SwayDA-ML-ND	0.646 ± 0.066	0.655 ± 0.049	−0.548	58	0.586	−0.141
Ankle proprioception*	0.733 ± 0.069	0.775 ± 0.040	−2.922	58	0.005	−0.754
Knee proprioception*	0.712 ± 0.047	0.754 ± 0.047	−3.504	58	0.001	−0.906
Hip proprioception*	0.602 ± 0.043	0.628 ± 0.035	−2.580	58	0.012	−0.667

LBP, low back pain; SwayDA-AP, Sway Discrimination Apparatus test – anterior–posterior sway; SwayDA-ML-D, Sway Discrimination Apparatus test – medial–lateral sway to the dominant side; SwayDA-ML-ND, Sway Discrimination Apparatus test – medial–lateral sway to the non-dominant side.

* Significant difference between groups.

Relationship Between Lower Limb Proprioception and Somatosensory Acuity

The results of Pearson’s correlation analysis are shown in Table 2. The proprioceptive acuity ankle and knee were significantly correlated with the SwayDA-AP test and the SwayDA-ML-D test (0.263 ≤ r ≤ 0.498, all p < 0.05). Hip proprioception was significantly correlated with the SwayDA-ML-ND test (r = 0.365, p = 0.004). However, no significant correlations were found between the ankle, knee, and hip proprioception (all p > 0.05), consistent with previous research (Han et al., 2013).

TABLE 2. Pearson’s correlations between lower limb proprioception and somatosensory perception during voluntary postural control in the 60 participants.

	Ankle proprioception	Knee proprioception	Hip proprioception
SwayDA-AP	0.288*	0.263*	0.031
SwayDA-ML-D	0.498**	0.285*	0.242
SwayDA-ML-ND	0.208	0.133	0.365**

SwayDA-AP, Sway Discrimination Apparatus test – anterior–posterior sway; SwayDA-ML-D, Sway Discrimination Apparatus test – medial–lateral sway to the dominant side; SwayDA-ML-ND, Sway Discrimination Apparatus test – medial–lateral sway to the non-dominant side.

* Correlation is significant at the .05 level (2-tailed).

** Correlation is significant at the .01 level (2-tailed).

To quantitatively analyze the contribution of lower limb proprioception to somatosensory acuity in voluntary postural sway, linear regression analysis was used with the dependent variables being the SwayDA tests and independent variables being the AMEDA tests. Ankle proprioception was the only significant independent variable that was associated with somatosensory acuity in anteroposterior sway (F = 5.233, p = 0.026, t_Ankle = 2.288, p = 0.026, adjusted R² = 0.067) and mediolateral sway to the dominant side (F = 19.152, p < 0.001, t_Ankle = 4.376, p < 0.001, adjusted R² = 0.235). Hip proprioception was found to be significantly associated with somatosensory acuity in mediolateral sway to the non-dominant side (F = 8.941, p = 0.004, t_Hip = 2.990, p = 0.004, adjusted R² = 0.119).

DISCUSSION

This study aimed to differentiate proprioceptive acuity of the ankle, knee, and hip in a cohort of adults with LBP age matched with asymptomatic controls; and to quantitatively describe the association between lower limb proprioception and somatosensory perception related to voluntary postural sway control. The results showed that the proprioception acuity scores for the ankle, knee, and hip in the LBP group were significantly lower than those in the control group. There were no significant correlations between ankle, knee, and hip proprioception scores, consistent with previous research using AMEDA tests (Han et al., 2013). Further regression analysis showed that ankle and hip proprioception were two significant sources that contributed to the somatosensory perception during voluntary postural control tasks, albeit with low level of association.

Previous studies on the alteration of somatosensory perception in patients with LBP have focused on the lumbar proprioception, and a negative change was found in the sense of position and movement (Ghamkhar & Kahlaee, 2019; Korakakis et al., 2021; Tong et al., 2017). In our study, there was global impairment of ankle, knee, and hip proprioception in patients with LBP. Among the lower limb joint complexes, other evidence shows that ankle proprioception is a key indicator for voluntary postural control related to sports performance (Han et al., 2015). The high scores in the ankle AMEDA tests were associated with better functional performance in surfing (Dowse et al., 2021) and football (Han et al., 2014), suggesting the fundamental role of ankle proprioception in posture feedforward for sports performance. The ankle AMEDA was also recommended for use in measuring readiness to return to sport (Stokes et al., 2020), where low scores on the test indicated an increased risk of recurrent sports injuries (Witchalls et al., 2012).

Our study demonstrated that diminished ankle and hip proprioception could partially account for the reduction of somatosensory acuity, suggesting that proprioceptive signal input from the ankle and hip joints may be an important source of somatosensory perception in voluntary postural control tasks. The hip joint, as the lower limb component connected to pelvis, is directly affected by an adjacent anatomical structure, the lumbar spine. There is a comorbidity pattern of the lumbar spine and hip joints, whereby LBP can affect the sensorimotor function of the hip joint, and vice versa (Redmond et al., 2014), which is consistent with the results of our study, further supporting the interconnected relationship between the lumbar spine and hip joints in the context of proprioceptive and sensorimotor function. Due to the decline in hip proprioception, patients with LBP had worse performance in postural sway control tasks, and may even fail to maintain balance, compared to the healthy controls (Mok et al., 2004). With regard to ankle proprioception, people with LBP rely on an ankle strategy in postural control tasks where they are reacting against an external disturbance, which requires the somatosensory cortex to increase the relative weighting of proprioceptive signals from the ankle (Claeys et al., 2015; Pinto et al., 2020). However, the model constructed in this study showed that the goodness of fit in predicting variation in somatosensory perception through lower limb proprioception only ranged from 0.067 to 0.235, which contradicts the view that proprioception is the dominant source for somatosensory perception (Peterka, 2018). One possible explanation is that the adjustment of somatosensory perception caused by proprioceptive damage might be compensated by other sensory inputs (e.g. visual inputs and vestibular inputs) in the young population, indicating a low synchronization between lower limb proprioceptive and somatosensory changes as reflected by adjusted R² in this study.

The overall decline in lower limb proprioception and somatosensory perception cannot be solely attributed to the impact of pain on peripheral proprioceptive receptors (Brumagne et al., 2019). Proprioceptive signals originate from various sources, including muscles, tendons, joints, and skin. Therefore, the interference effect of pain on proprioception signals from a single source, such as muscle spindles, may be compensated for by other proprioceptive mechanoreceptors located on the skin (Macefield, 2021). However, some explanations about the central mechanism of the decline in lower limb proprioception and somatosensory perception in LBP may be tenable. Cognitive adjustment induced by pain is a significant factor (Moriarty et al., 2011), and there is a higher risk of suffering from mild cognitive impairment in patients with LBP than there is in age-matched healthy controls (Corti et al., 2021). Specifically, evidence supports the view that the impairments in cognitive domains caused by LBP include working memory (Berryman et al., 2013), attention (Schiltenwolf et al., 2017), and executive function (Berryman et al., 2014). The methodology of assessing ankle, knee, and hip proprioception and somatosensory perception in this study requires a higher involvement of cognitive resources, as participants need to focus on the relevant continuum and judge different movement extents during the SwayDA and AMEDA tests. While some studies have explored the impairment in lower limb proprioception and somatosensory perception in individuals with LBP, the underlying mechanisms, particularly those related to the neuroplasticity of the central nervous system, remain an area of ongoing investigation, and a consensus has not yet been reached (Brumagne et al., 2019; Goossens et al., 2019; Kregel et al., 2015). What has been agreed upon so far is that reorganization of somatosensory and motor cortices is associated with impaired proprioception and somatosensory perception (Brumagne et al., 2019), given that the integration of proprioceptive sensory afferent may be modulated by plastic adjustment of organization or excitability at the secondary somatosensory cortex (Goossens et al., 2019).

Study Strength and Limitations

The SwayDA and AMEDA are innovative devices with good ecological validity because of testing methods incorporating movement extent and limb endpoint position information (Chen et al., 2023; Han et al., 2016). The exploration of altered lower limb proprioception among patients with LBP remains limited within the existing literature. The results of this study clarified the impairment in multiple joints’ proprioception of the lower limbs and may be valuable in understanding lower limb proprioception mechanisms in voluntary postural control tasks.

There are still some limitations in this study. Patients with LBP showed a significant decrease in the SwayDA-ML-D test, compared to the controls, but not in the SwayDA-ML-ND test. It was possibly due to brain lateralization. Due to the inhibitory effect on the non-dominant hemisphere, the dominant hemisphere may be more sensitive to the flow of sensory inputs than the non-dominant side (Güntürkün et al., 2020; van der Knaap & van der Ham, 2011). Consequently, as the sensory input was impaired in the patients with LBP, the integration output of somatosensory perception in the dominant hemisphere may be more susceptible than the contrasting side. However, this explanation still needs to be confirmed by neuroimaging studies in the future. Additionally, this study did not involve multiple comparisons, as it aimed to investigate between-group differences in somatosensory perception and lower limb proprioception. Due to the differences in the SwayDA and AMEDA, the results from different devices, even though their outcome measures are AUC values, were not comparable. Both lower limb proprioception and somatosensory were collected in a laboratory environment, and the novel devices used in this study still require more evidence support before clinical applications. The participants included in this study are young adults with mild pain, so it should be careful to interpret the results in different age groups and disability levels. This study only found low correlation coefficient between lower limb proprioception and somatosensory perception, which may be due to insufficient exploration of confounding factors related to somatosensory perception. Future research needs to use visual and vestibular inputs as covariates and explore the impact of potential confounding factors on the association between lower limb proprioception and somatosensory perception.

Clinical Implications

The overall decline in lower limb proprioception observed here in the LBP group highlights the importance of clinicians regularly evaluating changes in lower limb proprioception in patients with LBP. Given that the proprioceptive signals from the ankle and hip play a critical role in somatosensory perception during voluntary postural control, future research could focus on investigating how voluntary postural control ability changes in patients with LBP, particularly from the perspective of kinematics and kinetics. Additionally, establishing a cohort of patients with LBP would be useful in research carried out to observe the effects of diminished lower limb proprioceptive acuity on sports performance and injury risk. Such a study could provide valuable insights into the impact of proprioceptive deficits on athletic performance and the potential consequences of increased vulnerability to sports injuries in individuals with LBP.

CONCLUSION

The findings of this study suggest that LBP is associated with global effects on proprioceptive afferents from lower limbs and the sensory organization process. Further, proprioception signals from the ankle and hip play crucial roles as two key sources of somatosensory perception during voluntary postural control tasks. An implication of this is that clinical practitioners should regularly screen for changes in lower limb proprioception in patients with LBP and evaluate the impact of impaired proprioception on somatosensory perception. In future studies, it would be valuable to explore the effect of diminished lower limb proprioceptive acuity and any changed kinematic and kinetic characteristics on voluntary postural control.

DATA AVAILABILITY

The data that support the findings of this study are available from the corresponding author, ZC, upon reasonable request.

DISCLOSURE STATEMENT

None declared.

FUNDING

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.