Relationship between Hip Joint Position Sense and Balance Abilities

1. Introduction

Calmly standing still with balance is one of the most common postures that humans use to interact with the surrounding environment.¹ To maintain a stable standing posture, the body receives information through visual, vestibular, and proprioceptive senses. Among these senses, proprioception enables normal motor control from the central nervous system by providing information about all joint movements that are involved in body movement, as well as protecting the joints from external injuries.² Joint proprioception is broadly divided into joint position sense (JPS) and motor sense.³ JPS is strongly correlated with motor functions that are used to maintain balance.^4,5

As a strategy to maintain balance, the inverted pendulum model, which stresses ankle movement, has been proposed. This was followed by the double inverted pendulum model, which focuses on both ankle and hip joint movements.⁶ The ankle joint strategy is the most widely used strategy for activities of daily living. It has been widely accepted that with the ankle joint strategy, the body responds to even small sways, whereas the hip joint strategy is recruited to maintain balance by compensating for sway that is not adequately addressed with the ankle joint strategy.^7-9

However, some recent studies have raised questions about these strategies according to the level of sway. In other words, these studies argue that the role of the hip joint may be equal or even greater than that of the ankle joint, even for small sways.^10,11 Considering that the hip joint is closer to the body’s center of mass than is the ankle joint, the hip joint may play a more important role in the precise control of center of mass.¹² Furthermore, the hip joint is an important structure that affects the body’s weight load distribution, and a functional impairment of the hip joint undermines one’s balance ability.¹³ Abduction of the hip joint is a particularly important movement for maintaining standing balance in relation to the ankle joint. Beckman and Buchanan (1995) suggested that an ankle injury is associated with the pattern of hip abductor mobilization¹⁴, and Friel et al. (2006) reported that changes in hip joint movement increases the vulnerability of the ankle joint for injury.¹⁵ Nguyen et al. (2011) stated that weakening of the hip abductor muscles has an adverse effect on leg alignment.¹⁶ In light of these findings, we can infer that hip abduction plays an important role in maintaining balance and achieving a balanced standing posture.

Nevertheless, there is a lack of studies investigating the potential correlation between JPS during hip abduction and balance ability overall, as well as correlations in relation to the level of sway.

In this context, this study aimed to investigate the correlation between JPS during hip abduction and balance ability in relation to level of sway.

2. Methods

2.1 Participants

Sample size was computed using the G*power 3.1.5 software, with reference to Ha et al.’s (2013) study (α = 0.05, power = 0.90).¹⁸ Calculated sample size was 21 (actual power = 0.90); therefore, we enrolled 22 participants (9 males, 13 females) in consideration of potential dropouts. Our study was approved by the Institutional Review Board of the U1 University (U1 University IRB 2017-5).

The specific inclusion criteria were as follows:

· Individuals with a visual or vestibular disorder without history of falling in daily life.
· Individuals without a musculoskeletal or neurologic disease or injury.
· Individuals who voluntarily consented to participate in this study.

The demographic characteristics of the participants are shown in Table 1.

Table 1

Participant demographic characteristics

3. Results

Hip JPS error was moderately correlated to the total score and medial-lateral subscores of balance ability at all sway levels (r > 0.30, p < 0.05). Conversely, hip JPS error and the anterior-posterior (AP) balance score were moderately correlated at level 7, but not at levels 12 and 3 (Table 2).

Table 2

Correlation between joint position sense during hip abduction and balance ability in relation to sway level

4. Discussion

This study aimed to investigate the correlation between JPS during hip abduction and balance ability in relation to level of sway. A smartphone application was used to measure the JPS for hip abduction. Despite its importance, JPS is not widely measured in clinical practice, largely because existing equipment is too expensive and takes up too much space. On the other hand, smartphones are easily accessible and are not spatially restricted. Furthermore, JPS measurements using a smartphone have high reliability and high concurrent validity with an electrogoniometer.^20,21 Hence, we used a smartphone application to measure JPS of the hip joint in this study.

In a prior study, hip abduction was measured with a smartphone attached either to the thigh or the shin, and both methods had reliabilities exceeding 80%. It was difficult to attach the smartphone to the thigh with a regular armband in some participants, but attaching the smartphone to the shin was not difficult in most participants. Thus, in this study, we chose to attach the smartphone to the shin, as this was easier and yielded more reliable results.

Our results showed that JPS of the hip joint was significantly correlated with balance ability, which is supported by several previous studies. For example, Garland et al. (2009) suggested that a sensory deficiency affects balance ability,²² and Park (2010) stated that weakening of hip proprioception has adverse effects on postural alignment.²³ Many balance training programs stress sensory training of only the ankle joint, with great neglect of the hip joint.²⁴ However, Roerdink et al. (2009) argued that ankle sense (proprioceptive sense) does not affect balance in stroke patients,¹⁷ and Choi and Park (2011) suggested that individuals with better hip joint senses have better balance abilities.²⁵

In this study, we used three levels (12, 7, 3) of sway. Level 12 most closely resembles static balance with hardly any sway, while in a pilot study, level 3 was found to be the most difficult level in which participants maintained balance without falling. Existing balance strategies state that the ankle joint is used for small sways while the hip joint is used for larger sways; however, the present study found that JPS during hip abduction was significantly correlated with balance ability at level 12 as well, suggesting that the hip joint also plays a key role in small sway. Pertaining to this result, Shim (2016) suggested that sensory-motor training of the hip abductor muscles is beneficial for improving balance ability,²⁴ supporting the findings of this study. In addition, Choi and Park (2011) found that sense of light contact to the hip joint affects both dynamic and static balance abilities,²⁵ which was also in line with our findings.

Wilson et al. (2006) stated that the functions of the hip joint and ankle joint are complementary in terms of preventing injuries and maintaining and continuing balance in daily living.²⁶ Therefore, we suggest that balance training programs should also include hip sensory training.

This study had limitations. For example, this study was only conducted in healthy adults within a specific geographical region. Further, we only analyzed correlations, which have no implications for causal relationships. We also did not examine JPS of other joints. Therefore, we hope that future studies address these limitations in an effort to propose effective balance training methods.

5. Conclusions

This study investigated the correlation between JPS during hip abduction and balance ability in 23 healthy undergraduate students. The following results were found:

(1) Error of JPS during hip abduction was moderately correlated with the total score and medial-lateral subscore of balance ability at all sway levels.

(2) Error of JPS of hip abduction and AP balance score was moderately correlated at level 7, but not at levels 12 and 3.

As shown here, JPS during hip abduction was significantly correlated with balance ability, regardless of sway level. Therefore, sensory training of the hip joint, in addition to the ankle joint, should be adequately performed during balance training.

Acknowledgments

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (Ministry of Science, ICT & Future Planning) (No. NRF-2017R1C1B5014991).

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