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Abstract

BACKGROUND:

Ankle sprain is a common sports injury. The initial injury involves trauma, but repeated inversion injuries occur in patients with eversion strength weakness and lower dynamic balance ability.

OBJECTIVE:

This study aimed to measure strength and dynamic balance ability of ankle sprain patients and to analyze characteristics which part is more meaningful.

METHODS:

Patients were 91 men and 116 women with chronic ankle instability (CAI) All patients were tested for dynamic balance (Y-balance test, YBT) and isokinetic strength (evertors, at 30 ${}^{\circ}$ /s).

RESULTS:

Forty men (44.0%) and 44 women (37.9%) showed lower relative eversion strength on the injured side. Balance was compromised in 66 men (72%) and 74 women (81%). Sixteen men (17.6%) and 44 women (37.9%) were weak in both YBT and muscle strength.

CONCLUSIONS:

CAI patients tended to have a greater loss of dynamic balance ability than weakness of ankle eversion strength. Therefore, balance training should be emphasized in ankle re-injury prevention program.

Keywords

Ankle sprain balance strength

1. Introduction

Ankle sprain is a common sport-related injury, with a prevalence of 10–28% among all athletes [1]. According to a previous study, 48.3% of athletes had bilateral injuries and 51.8% had unilateral injuries, while 30,000 people with injuries visit the emergency department a day in the United States [2, 3]. This common sports injury occurs frequently in non-athletes. Most cases occurred during recreational physical activities but also frequently occur in unstable situations such as walking, climbing up and down stairs, and falling [4]. In the United States, the incidence is 2.15 per 1,000 person-years of the total population, and at the age of 15–19 years, when physical activity level is high, the incidence is as high as 7.2 per 1,000 person-years [5]. Although the initial injury in an ankle sprain occurs acutely, it tends to become chronic in 20% of patients, and an incompletely healed ankle is accompanied by functional instability resulting in chronic ankle instability (CAI) [3]. Ankle sprain occurs in sports situations during foot inversion from the ground in highly dynamic situations such as those in basketball and soccer [6]. Immediately after the injury, patients feel intense pain, with swelling and tenderness [5]. Although a previous study reported positive surgical outcomes, considering the time and cost of returning to sports activities, whether surgery is more effective than non-surgical treatments is controversial [7]. Rehabilitation is highly important in conservative treatment, and this is aimed at preventing problems, with a 50% rate of re-injury and functional recovery [8]. In general, rehabili-tation consists of balance training, strength, and plyometric, and several studies reported positive results [5]. Emphasis on this exercise is based on the fact that previous studies showed deficits in the strengths of eversion and plantar flexion [9, 10]. Patients with CAI have sensorimotor deficits, and re-injury prevention studies have shown similar results. When the preventive effects of strength and balance training were analyzed, the incidence rate was significantly reduced in the ba-lance exercise group [11, 12] In addition, strength training did not enhance sensory motor function [13].

The aim of this study was therefore to analyze the characteristics of strength and dynamic balance ability in non-athlete patients, women and men, afflicted by ankle CAI with the purpose of quantifying strength and balance ability deficits.

2. Methods

2.1 Subjects

A group of 207 patients, 116 women and 91 men, not involved in athletic activities who visited a medical center (Sport and Health Medicine Center of Seoul Asan Medical Center, Seoul, Korea) with major symptoms of CAI or sprained ankle were recruited. Their anthropometric characteristics are outlined in Table 1. Orthopedic surgeons selected patients who were not candidates for surgery on the basis of radiological and clinical evidence. Exclusion criteria included 1) bilateral injury, 2) not completing all scheduled tests, 3) acute pain and inability to stand on one foot, 4) pain that restricts isokinetic strength testing and 5) lack of information regarding the minimum range of motion (ROM) required for isokinetic testing; approximately inversion 20–25 ${}^{\circ}$ and eversion 10–15 ${}^{\circ}$ [14]. This study was approved by the Institutional Review Board of Asan Medical Center, which is a tertiary referral hospital (2019-0242).

2.2 Isokinetic testing

Eversion strength was measured using a CSMi isokinetic dynamometer and HUMAC software (CSMi HUMAC NORM, USA). The test methods were performed based on the existing manual and literature [15, 16]. The patients’ height and body weight were measured electronically using auto weight and height measure system GL-150RP (G-Tech International, Korea). The test was conducted with concentric contraction. The subjects’ position was based on the standard guidelines of the measuring machine company [15]. Subjects were instructed to bend their hips and knees at 80–110 ${}^{\circ}$ while assuming the supine position. The height of the foot was adjusted so that the knees and heel were both positioned horizontally. The foot and footplate were aligned and fixed using a strap. The thigh, hip, and torso were fixed with a pad, strap and belt, and handheld handrail, respectively. The 0 ${}^{\circ}$ point was set at the neutral position of the foot, and during the test, the ROM was set at 30–35 ${}^{\circ}$ inversion and 20–25 ${}^{\circ}$ eversion. The test started with a 30 ${}^{\circ}$ eversion. After the maximum contraction of the invertor, the contraction of the evertor was performed to return to the starting position.

Before the test, subjects performed warm-up exercises. To comprehensively understand the test, sufficient explanation was provided to all subjects and appropriate and adequate practices were performed. To induce the subjects’ familiarity with the machine before the actual test, submaximal movement was performed several times at high speed (120 ${}^{\circ}$ /sec) and low speed (30 ${}^{\circ}$ /sec), and the actual test was performed with the subjects’ consent.

After the subjects were already familiar with the machine, the actual test was repeated 4 times at 30 ${}^{\circ}$ /sec. In the analysis, absolute value and relative value were used with peak torque. The absolute value is the peak torque value (Nm), and the relative value is the deficit (%) as follows: 100 – ([uninjured side – injured side]/uninjured side) $\times$ 100. For maximum strength expression, the examiner provided an oral encouragement.

The analysis was performed in the following two ways. (1) The subjects were classified into two groups based on their absolute eversion muscle strength (men, 28 Nm; women, 20 Nm). Moreover, subjects with absolute eversion muscle strength $\geqslant$ 28 Nm and $\leqslant$ 27 Nm were assigned in the normal strength group and the weak strength group, respectively [16]. (2) Based on the relative eversion strength concept, the normal deficit range was within $\pm$ 15%. This refers to the fact that approximately 15% of the dominant and non-dominant differences are observed in a previous Korean study [17]. Therefore, the normal strength group had a 0%–15.0% deficit in the injured side, and the weak strength group had a 15.1% or higher deficit [18].

Table 1
Characteristics of the subjects

	Men ( $n=$ 91)	Women ( $n=$ 116)	$p$
Age, years	32.4 $\pm$ 11.3	36.0 $\pm$ 12.2	0.018 ${}^{*}$
Height, cm	174.6 $\pm$ 5.8	160.9 $\pm$ 5.2	$<$ 0.001 ${}^{*}$
Weight, kg	76.4 $\pm$ 12.4	59.2 $\pm$ 9.3	$<$ 0.001 ${}^{*}$
BMI, kg/m ${}^{2}$	25.0 $\pm$ 3.6	22.9 $\pm$ 3.4	$<$ 0.001 ${}^{*}$
Injury side (left/right)	52/44	57/59	0.585
Y-balance test difference, $n$ (%)
Normal	25 (27.5%)	42 (36.2%)	0.441
One direction deficit	28 (30.7%)	40 (34.5%)
Two direction deficit	22 (24.2%)	21 (18.1%)
Three direction deficit	16 (17.6%)	13 (11.2%)
Absolute strength deficit, $n$ (%)
Men $\geqslant$ 28 Nm, Women $\geqslant$ 20 Nm (normal)	24 (26.4%)	25 (21.6%)	0.521
Men $\leqslant$ 27 Nm, Women $\leqslant$ 19 Nm (weak)	67 (73.6%)	91 (78.4%)
Relative strength deficit, $n$ (%)
$\leqslant\pm$ 15.0% (normal)	51 (56.0%)	72 (62.1%)	0.880
$>$ $-$ 15.1% (weak)	40 (44.0%)	44 (37.9%)

${}^{*}p<$ 0.05; BMI, body mass index.

Table 2

Comparison of YBT result and strength between the injured and healthy sides

	Men			Women
	Injured side	Uninjured side	$p$	Injured side	Uninjured side	$p$
YBT
ANT, cm	53.6 $\pm$ 7.7	58.4 $\pm$ 8.6	$<$ 0.001 ${}^{*}$	50.0 $\pm$ 9.4	53.7 $\pm$ 7.6	$<$ 0.001 ${}^{*}$
PM, cm	84.3 $\pm$ 16.8	89.9 $\pm$ 12.1	$<$ 0.001 ${}^{*}$	76.8 $\pm$ 14.8	81.7 $\pm$ 10.5	$<$ 0.001 ${}^{*}$
PL, cm	83.8 $\pm$ 14.2	87.1 $\pm$ 14.8	0.009 ${}^{*}$	74.7 $\pm$ 13.9	79.2 $\pm$ 10.6	$<$ 0.001 ${}^{*}$
Score	83.2 $\pm$ 12.3	88.5 $\pm$ 10.9	$<$ 0.001 ${}^{*}$	81.8 $\pm$ 14.2	87.1 $\pm$ 10.7	$<$ 0.001 ${}^{*}$
Isokinetic strength
Eversion, Nm	23.8 $\pm$ 8.8	27.4 $\pm$ 9.4	$<$ 0.001 ${}^{*}$	15.3 $\pm$ 6.1	16.7 $\pm$ 6.5	$<$ 0.001 ${}^{*}$
Eversion, Nm/kg	29.8 $\pm$ 13.5	34.3 $\pm$ 14.5	$<$ 0.001 ${}^{*}$	25.1 $\pm$ 10.7	27.2 $\pm$ 10.4	0.003 ${}^{*}$

${}^{*}p<$ 0.05; ANT, anterior; PM, posteromedial; PL, posterolateral.

2.3 Y balance test

Dynamic balance ability was measured using a Y-balance test (YBT) equipment (Y Balance Test ${}^{\rm TM}$ , USA). The examiner first demonstrated to the patient how to perform the test and subsequently allowed the patient to take time to practice. The higher value between two successful measurements was recorded. The shoe was taken off, and the test was performed on the injured side first. If the foot touched the ground or lost its center, the test is considered a failure [19]. According to the previous studies, differences in the anterior (ANT) direction of $>$ 4 cm were considered significant [20]. Therefore, in our study, a difference of $>$ 4 cm in each direction was considered as a “deficit” and applied to all three directions [21]. Examinations were performed according to the established guidelines. The ANT, posteromedial (PM), and posterolateral (PL) directions were recorded in centimeters and calculated as follows: ([3 directions/3 $\times$ limb length]) $\times$ 100. Limb length was measured using a flexible tape measure from the superior iliac spine to the distal tip of the ipsilateral medial malleolus [22].

2.4 Statistical analysis

Statistical analysis was conducted using SPSS 25.0 (SPSS Inc., USA). The patients’ general characteristics were analyzed according to sex, and the relationship between isokinetic strength and YBT result was analyzed. The mean and standard deviation were calculated, and independent $t$ -test and chi-square test were performed for characteristic of subjects. Paired $t$ -test was used to confirm the difference between the injured and uninjured sides. The significance level was set at $p$ values of $<$ 0.05.

3. Results

3.1 General characteristics: Strength and Y-balance

Age was significantly lower in the men than in the women (32.4 $\pm$ 11.3 vs 36.0 $\pm$ 12.2 years; $p=$ 0.018). Significant differences were found in height, weight, and body mass index ( $p<$ 0.001). In the YBT, 27.5% of the men and 36.2% of the women had normal values. In the relative strength, 56.0% of the men and 62.1% of the women had normal results. The chi-square test results in YBT and strength test showed no significant difference between women and men (Table 1). Table 2 shows the strength and YBT results of the injured and uninjured sides. In all the variables, the injured side was weaker and had lower balance ability than the uninjured side in men and women.

3.2 Y-balance according to eversion strength

Table 3 presents the results of the analysis of YBT according to absolute muscle strength. Of the men, 67 had weakness while 24 had normal strength. The overall balance function of the injured sides were significantly lower than that of the uninjured sides. No significant differences in scores were found in PM direction in the patients with $\geqslant$ 28 Nm, but significant decreases were observed in the ANT and PL. For the women, all score of the injured side were lower than the uninjured side. Table 4 used the relative strength concept as follows: deficit $\leqslant\pm$ 15.0% for normal strength group and $\geqslant$ $-$ 15.1% for the weakness group. Forty men (44.0%) and 44 (37.9%) women had low muscle strength. In both sexes, YBT scores were significantly lower regardless of relative muscle strength.

Table 3
YBT function according to absolute isokinetic eversion strength class

	Weakness strength		Normal strength
	Injured	Uninjured	Injured	Uninjured
Men	$\leqslant$ 27 Nm ( $n=$ 67)		$\geqslant$ 28 Nm ( $n=$ 24)
ANT, cm	52.9 $\pm$ 7.5	58.3 $\pm$ 8.7 ${}^{*}$	55.6 $\pm$ 8.6	59.3 $\pm$ 9.2 ${}^{*}$
PM, cm	82.0 $\pm$ 17.8	88.8 $\pm$ 12.6 ${}^{*}$	91.1 $\pm$ 11.8	93.5 $\pm$ 10.3
PL, cm	82.2 $\pm$ 15.7	87.1 $\pm$ 12.5 ${}^{*}$	86.5 $\pm$ 14.2	90.8 $\pm$ 11.5 ${}^{*}$
Score	82.4 $\pm$ 12.0	88.0 $\pm$ 11.2 ${}^{*}$	86.2 $\pm$ 11.8	90.0 $\pm$ 10.3 ${}^{*}$
Women	$\leqslant$ 19 Nm ( $n=$ 91)		$\geqslant$ 20 Nm ( $n=$ 25)
ANT, cm	48.6 $\pm$ 9.5	52.8 $\pm$ 7.4 ${}^{*}$	54.8 $\pm$ 8.1	57.2 $\pm$ 8.1 ${}^{*}$
PM, cm	76.1 $\pm$ 15.4	81.3 $\pm$ 10.8 ${}^{*}$	79.5 $\pm$ 11.8	82.7 $\pm$ 10.0 ${}^{*}$
PL, cm	73.8 $\pm$ 14.2	78.9 $\pm$ 10.3 ${}^{*}$	77.2 $\pm$ 12.7	79.7 $\pm$ 12.3 ${}^{*}$
Score	81.1 $\pm$ 14.9	87.1 $\pm$ 10.6 ${}^{*}$	83.9 $\pm$ 11.8	87.0 $\pm$ 11.6 ${}^{*}$

${}^{*}p<$ 0.05; ANT, anterior; PM, posteromedial; PL, posterolateral.

Table 4

YBT function according to relative isokinetic eversion strength class

	Weakness strength		Normal strength
	Injured	Uninjured	Injured	Uninjured
Men	$\geqslant$ 15.1% ( $n=$ 40)		$\leqslant$ $n$ $\pm$ 15.0% ( $n=$ 51)
ANT, cm	53.1 $\pm$ 7.9	56.8 $\pm$ 8.2 ${}^{*}$	53.8 $\pm$ 8.6	58.8 $\pm$ 8.6 ${}^{*}$
PM, cm	83.3 $\pm$ 16.1	90.2 $\pm$ 12.9 ${}^{*}$	85.5 $\pm$ 19.3	91.3 $\pm$ 11.8 ${}^{*}$
PL, cm	81.6 $\pm$ 14.4	86.5 $\pm$ 13.9 ${}^{*}$	86.6 $\pm$ 12.7	89.9 $\pm$ 10.7 ${}^{*}$
Score	81.7 $\pm$ 11.9	87.5 $\pm$ 11.4 ${}^{*}$	85.5 $\pm$ 13	90.9 $\pm$ 10.1 ${}^{*}$
Women	$\geqslant$ 15.1% ( $n=$ 44)		$\leqslant$ $\pm$ 15.0% ( $n=$ 72)
ANT, cm	46.2 $\pm$ 10.9	52.1 $\pm$ 7.3 ${}^{*}$	52.1 $\pm$ 7.5	54.8 $\pm$ 8.6 ${}^{*}$
PM, cm	72.4 $\pm$ 17.8	79.8 $\pm$ 10.4 ${}^{*}$	78.6 $\pm$ 10.9	81.7 $\pm$ 8.9 ${}^{*}$
PL, cm	69.7 $\pm$ 16.1	77.1 $\pm$ 10.4 ${}^{*}$	76.4 $\pm$ 11.5	79.2 $\pm$ 10.8 ${}^{*}$
Score	76.2 $\pm$ 17.1	84.6 $\pm$ 10.4 ${}^{*}$	84 $\pm$ 10.8	87.5 $\pm$ 10.3 ${}^{*}$

${}^{*}p<$ 0.05; ANT, anterior; PM, posteromedial; PL, posterolateral.

3.3 Eversion strength according to YBT result

Eversion strength was compared between the injured and uninjured sides according to the number of direction deficits. Among the men, 66 had deficits (one deficit in 28, two deficits in 22 and three deficits in 16 men). No significant strength differences were found between normal to 2 direction deficits, but the eversion strength was significantly lower with 3 deficits in 16 men (17.6%). Among women, 74 had deficits (one deficit in 40, two deficits in 21 and three deficits in 13 women). The eversion strength was not significantly lower with 0 or 1 deficit, but was significantly lower with 2 and 3 deficits in 44 women (37.9%).

4. Discussion

Ankle sprain is traditionally one of the most common sports injuries caused by trauma and is likely to occur during landing, cutting, and direction chan-ges [23]. In non-sports cases, it can also occur while walking up or down the stairs or as a result of falling [4]. However, repetitive injury occurs frequently, with recurrence rates of over 75%, eventually leading to CAI [24].

The most common condition in CAI patients is a loss of balance ability and weak muscle strength [25]. The balance ability, specifically the dynamic balance, is controlled to constantly center the body while moving, such as walking or running, and the organs that are usually affected with balance ability include the vision, vestibule, and somatosensory system [26]. Therefore, considering the improvement of the dynamic ba-lance in rehabilitation, the sensory motor function is restored and the possibility of reinjury is reduced. On the contrary, the damaged part is accompanied by a weakening of the sensory motor function and dynamic balance. Several documents have reported weakening of the dynamic balance in CAI patients [27, 28]. Hence, the researchers assessed the effects of dynamic balance training in CAI patients. Sefton et al. found that sensorimotor function improved after 6 weeks of balance training in an average 21.2-year-old CAI subject [29]. According to the study of Schaefer and Sandrey, star excursion balance test (SEBP), ROM, and ankle function improved after 4 weeks of dynamic balance training, which was performed in a shorter period of time, in 45 high school and college students with CAI [30].

Additionally, balance training prevents reinjury. According to a previous study, a 1-year follow-up period of CAI patients showed that only 7% of reinjury were observed in the balance-trained group, but 29% of injuries were observed in the non-trained group [15]. Similarly, based on another study with a 230-day follow-up period, the recurrence rates of injury were 25% and 54% in the training group and the non-training group, respectively [31].

Muscle weakness in CAI patients is as common as balance loss. Since ankle sprains are injuries mostly caused by inversion, evertor weakening is usually observed in ankle sprains [32, 33]. In this study, the strength and YBT values were significantly lower on the injured side than on the non-injured side; this was observed in both sexes (Table 2). According to several previous studies, ankle sprain or CAI resulted in weak balance ability and strength, and this result is consistent with the result of the present study [10, 12, 34].

However, our researchers wanted to determine which factors of balance and strength are more common in CAI patients. Therefore, we analyzed the balance ability according to strength and, on the contrary, the strength according to balance ability in detail.

Tables 3 and 4 show the dynamic balance ability according to muscle strength. The result was a reduction in balance ability, regardless of whether the muscles were high or low.

Table 5
Eversion strength according to YBT class

	Normal		1 direction deficit		2 direction deficits		3 direction deficits
	Injured	Uninjured	Injured	Uninjured	Injured	Uninjured	Injured	Uninjured
Men	( $n=$ 25)		( $n=$ 28)		( $n=$ 22)		( $n=$ 16)
Eversion, Nm	23.4 $\pm$ 9.2	27.2 $\pm$ 8.3	25.0 $\pm$ 7.9	27.6 $\pm$ 8.4	24.8 $\pm$ 9.6	27.8 $\pm$ 10.5	21.1 $\pm$ 9.0	26.8 $\pm$ 11.8 ${}^{*}$
Eversion, Nm/kg	31.5 $\pm$ 12.4	36.2 $\pm$ 10.2	31.8 $\pm$ 10.6	35.1 $\pm$ 11.2	33.0 $\pm$ 13.5	37.2 $\pm$ 14.7	27.1 $\pm$ 12.9	34.4 $\pm$ 17.1 ${}^{*}$
Women	( $n=$ 42)		( $n=$ 40)		( $n=$ 21)		( $n=$ 13)
Eversion, Nm	16.2 $\pm$ 4.9	16.6 $\pm$ 6.5	16.2 $\pm$ 6.6	17.4 $\pm$ 6.9	15.9 $\pm$ 6.8	18.8 $\pm$ 7.1 ${}^{*}$	9.3 $\pm$ 3.9	15.4 $\pm$ 4.2 ${}^{*}$
Eversion, Nm/kg	27.8 $\pm$ 8.1	27.9 $\pm$ 9.0	26.8 $\pm$ 11	28.5 $\pm$ 10.7	25.6 $\pm$ 11.9	29.9 $\pm$ 11.9 ${}^{*}$	15.6 $\pm$ 5.6	26.1 $\pm$ 6.4 ${}^{*}$

${}^{*}p<$ 0.05.

In contrast, Table 5 shows muscle strength according to balance ability. Muscle weakness was observed only in CAI patients with severely reduced balance ability, but strength loss was not observed in CAI patients with mildly reduced balance ability. In conclusion, balance ability weakness is more pronounced compared to muscle weakness in CAI patients.

These findings are the most representative results of this study. These results indirectly explain that balance is the most important exercise in strength and balance in CAI patients. However, to further strengthen these findings, a case control study distinguishing the strength group from the balance group and testing the efficacy of the exercise training is required. Moreover, a long-term follow-up study determining the most effective exercise that further reduces the recurrence rate of injury is necessary.

In general, the order of musculoskeletal rehabilitation includes ROM, strength, and functional training (e.g., balance, neuromuscular system, sensory motor, and motor learning) [5]. The key to rehabilitation for ankle sprain or CAI is to ensure that the ankle remains stable in dynamic situations. Factors contributing to the stability of the ankle are the morphological characteristics of the ligaments and muscles. Muscle strength and balance ability are the areas that can be improved through training.

This study is characterized by the relatively large sample size, but has the following limitations. The hospital in which the study was conducted was a large tertiary general facility, which means that the injured patients had to go through local hospitals and wait to visit medical centers after the injury. Therefore, the results may differ according to the acute and chronic phases of the injury due to the inevitable delays (up to several months) until the visit.

This was conducted with cross-sectional design. Therefore, strength and balance training programs should be compared by conducting pretests and post-tests using case-controlled follow-up studies in further study.

5. Conclusion

Weakening of strength and balance ability in patients with CAI and ankle sprain was found clinically significant. Regardless of evertor strength, weakening of balance ability was observed in all groups. However, weakening of strength was observed in severe loss of balance ability subjects. Therefore, balance ability deficit in CAI patients is more prominent than strength deficit; In conclusion, balance training should be emphasized to prevent re-injury of ankle sprain.

Footnotes

Acknowledgments

This study was supported by a grant (2018-0808) from the Asan Institute for Life Sciences, Asan Medical Center, Seoul, Korea.

Conflict of interest

The authors declare no conflicts of interest.

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Characteristics of the balance ability and isokinetic strength in ankle sprain

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Methods

2.1 Subjects

2.2 Isokinetic testing

Table 1 Characteristics of the subjects

2.4 Statistical analysis

3. Results

3.1 General characteristics: Strength and Y-balance

3.2 Y-balance according to eversion strength

Table 3 YBT function according to absolute isokinetic eversion strength class

4. Discussion

Table 5 Eversion strength according to YBT class

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Characteristics of the subjects

Table 3
YBT function according to absolute isokinetic eversion strength class

Table 5
Eversion strength according to YBT class