Keywords
dominant foot - muscle strength - balance - foot and ankle outcome score
Introduction
Chronic ankle instability (CAI) is persistent instability following an ankle sprain
that causes the ankle to repeatedly give way, resulting in functional limitations.
This condition, affecting about 25% of people with sprained ankles, can lead to
long-term consequences, such as ankle arthritis, significantly affecting quality of
life [1].
Limb dominance is a tendency of a person to favor one leg over the other during
activities requiring unilateral movement or support, such as kicking balls, stepping
onto a box, balancing after a posterior push, or standing on one leg. Various
factors, including genetics, injury history, and training, contribute to determining
limb dominance [2]
[3]. The dominant foot (DF), which is
typically used more during physical activities, may exhibit greater strength and
balance than the nondominant foot (non-DF) [3]
[4]. Thus, the presence of
CAI in the dominant leg could affect the function and symptoms.
Limb dominance may predict lateral ankle sprains and increase the risk of lower
extremity injuries. However, several studies have found no significant difference
in
injury rates between dominant and nondominant ankles [2]
[3]
[4]
[5]
[6]. These studies mainly analyzed the influence of limb dominance on
athletes with CAI. Studies on how limb dominance affects nonathletes with CAI are
lacking.
DF affected by CAI may show reduced strength and balance compared with non-DF. Our
study aimed to examine preoperative differences in strength and balance between the
DF and non-DF of individuals undergoing ligament stabilization surgery in the
general population.
Materials and Methods
Our institutional review board approved this study (Institutional Review Board No.
2022–09–031). Informed consent was waived due to the retrospective design of the
study. We reviewed the medical records of all patients with a lateral CAI who
visited our hospital between March 2020 and March 2023. Patients with records of
open or arthroscopic lateral ligament stabilization surgery and preoperative
evaluation, including isokinetic dynamometric strength evaluation, Y-balance test
(YBT), and Foot and Ankle Outcome Score (FAOS), were included in the study.
All included patients underwent lateral ligament stabilization surgeries performed
by
a single surgeon. The choice of surgical procedure was based on the discretion of
the surgeon and the preference of the patient after being informed of the
procedures. The preoperative examination results did not influence the choice of
surgical method. Open surgery was preferred if the patient was active, such as
athletes or military personnel. Otherwise, arthroscopic surgery was preferred,
especially for those more sensitive to incisions, such as young women. The DF was
the preferred leg best able to kick a ball through a goal, as this is the most
effective assessment method [7]. Only
patients with a right-sided DF were included to minimize statistical error.
Exclusion criteria included patients with previous foot and ankle surgery; known
conditions such as tarsal coalitions, neuromuscular diseases, or recent trauma that
could interfere with the examination; incomplete medical examinations and records;
and generalized laxity with a Beighton score>4.
Isokinetic dynamometric strength evaluation
The isokinetic dynamometer (Cybex NORM®, Humac, CA, USA) was used to assess the
ankle evertor and invertor muscle strength. The patient assumed a sitting
position with the knee flexed at 90° and the thigh secured to the pad. The feet
were secured to the inspection device. The handles were gripped to keep other
body parts immobile, while the legs, waist, and torso were fixed to the seat.
The ankle was positioned with 10° plantar flexion in the foot adapter and
secured using two Velcro straps ([Fig.
1a]). An isokinetic test was performed in concentric mode for ankle
eversion and inversion at angular velocities of 30°/s (5 repetitions) and 120°/s
(10 repetitions). The test range was 30°–35° for ankle inversion and 25°–30° for
ankle eversion [8]. Three trials
were conducted before each test, with a 20-second rest between the trial and the
test and a 90-second rest between the two sets. The patients received
encouraging feedback to exert maximum effort. For accuracy, the strength of the
healthy ankle was measured before the injured foot was examined. The parameters
recorded included peak torque, time to reach peak torque, and work
performed.
Fig. 1 The position of the patient on the dynamometer to perform
the ankle evertor and invertor muscle strength test (a) and the
Y-Balance test (b).
Y-Balance test
The YBT was performed as a dynamic balance assessment using the YBT equipment
(FMS TM, Chatham, VA, USA) and following the recommended guidelines [9]. After the isokinetic strength
test, participants had a 20-minute rest. The YBT was performed by placing each
foot of the participants on the examination table with one foot positioned at
the center and extended as far as possible in the anterior, posterior lateral,
and posterior medial directions ([Fig.
1b]). Testing began with the healthy side, followed by the injured
side, with the examiner giving verbal instructions. Each side was tested three
times, and the highest recorded value was documented. The recordings were made
at 0.5 cm increments. If a loss of balance resulted in the foot touching the
ground, the test was repeated after an explanation. The examiner observed the
participants from behind to minimize distraction. The lower limb length was
measured from the anterior superior iliac spine to the middle of the medial
malleolus using a tape measure. The total score was calculated using the
following formula: ([sum of the three distances]/[lower limb length×3])×100.
Foot and ankle outcome score
The FAOS questionnaire was developed to assess symptoms or pain in various
situations related to foot and ankle problems [10]. A transculturally adapted FAOS
was used in this study [11].
Statistical analysis
Descriptive statistics (means, standard deviations, and proportions) were
calculated. A Kolmogorov-Smirnov test was used to assess the distribution
normality of continuous variables. Comparisons between DF and non-DF were
conducted using a t-test or a Mann-Whitney U test, depending on the data
characteristics. The isokinetic dynamometric strength evaluation and the YBT
results were analyzed for correlation with FAOS using Pearson’s correlation
coefficients. Statistical analyses were performed using SPSS version 20.0 (IBM
Co., Chicago, IL). P values<0.05 were considered significant.
Results
A total of 43 patients (24 men and 19 women) with right-side lateral CAI were
included ([Fig. 2]). The mean age at
the time of surgery was 34.1±15.1 years (range, 15–72). Of the 43 patients, 31 and
12 underwent open and arthroscopic surgeries, respectively. The surgery methods did
not influence the results, as the study was based on the preoperative evaluation.
A
total of 26 and 17 patients reported their affected right side as their DF and
non-DF, respectively. The mean FAOS score was 67.8±14.8 (range, 28–92). The mean
FAOS scores for patients with affected DF and non-DF were 65.7±16.2 and 71.0±12.1,
respectively. The mean FAOS scores for patients who had undergone open and
arthroscopic surgeries were 68.9±15.6 and 65.1±12.4, respectively ([Table 1]).
Fig. 2 Inclusion and exclusion criteria.
Table 1 Patient demographics.
|
Parameter
|
Measurements
|
95% CI
|
p-value
|
|
No. of subjects (Male/Female)
|
43 (24/19)
|
|
|
|
Laterality (Right:Left)
|
43/0
|
|
|
|
Age at operation (Mean±SD)
|
34.1±15.1 (15–72)
|
|
|
|
OP type (Arthroscopic/open surgery)
|
12/31
|
|
|
|
FAOS
|
67.8±14.8 (28–92)
|
|
|
|
DF
|
65.7±16.2
|
− 14.5–4.0
|
0.257
|
|
Non-DF
|
71.0±12.1
|
|
Arthroscopic surgery
|
65.1±12.4
|
− 14.0–6.4
|
0.457
|
|
Open surgery
|
68.9±15.6
|
Age at operation and FAOS; mean±standard deviation (range); Age=decimal
years; CI=confidence interval; DF=dominant foot; OP=operation.
[Table 2] compares the isokinetic
dynamometric evaluation of ankle evertor and invertor muscle strength and the YBT
between the DF and non-DF. There was no statistically significant difference between
the DF and non-DF regarding evertor and invertor muscle strength (p=0.082–0.951).
The YBT also showed no statistically significant difference between the two groups
in the anterior, posterior medial, and posterior lateral directions
(p=0.082–0.951).
Table 2 Comparison of preoperative measurements based on the
presence of dominant foot instability.
|
Measurements
|
DF
|
Non-DF
|
95% CI
|
p-value
|
|
Y balance
|
AN
|
|
− 5.5±6.0
|
− 6.8±11.4
|
− 4.0–6.7
|
0.621
|
|
PM
|
|
− 6.3±9.0
|
− 5.4±14.7
|
− 8.2–6.4
|
0.805
|
|
PL
|
|
− 5.1±9.1
|
− 8.1±7.3
|
− 2.3–8.3
|
0.264
|
|
Peak torque deficit (%)
|
Invertor
|
30º
|
20.5±26.0
|
25.2±30.2
|
− 22.2–12.7
|
0.587
|
|
120º
|
17.8±26.7
|
20.3±23.0
|
− 18.5–3.5
|
0.755
|
|
Evertor
|
30º
|
25.9±26.0
|
21.1±32.1
|
− 13.2–22.7
|
0.597
|
|
120º
|
18.3±20.7
|
20.7±23.8
|
− 16.2–11.4
|
0.731
|
|
Total work deficit (%)
|
Invertor
|
30º
|
21.9±31.1
|
30.6±32.2
|
− 28.6–11.1
|
0.381
|
|
120º
|
22.3±29.9
|
32.2±32.8
|
− 29.4–9.7
|
0.316
|
|
Evertor
|
30º
|
27.5±25.4
|
26.9±33.7
|
− 17.6–18.8
|
0.951
|
|
120º
|
23.1±23.7
|
28.6±28.9
|
− 21.7–10.8
|
0.503
|
|
Time to peak torque
|
Invertor
|
30º
|
0.14±0.28
|
0.02±0.31
|
− 0.07–0.30
|
0.220
|
|
120º
|
− 0.01±0.11
|
− 0.04±0.08
|
− 0.02–0.98
|
0.278
|
|
Evertor
|
30º
|
0.18±0.02
|
0.02±0.31
|
− 0.02–0.35
|
0.082
|
|
120º
|
0.01±0.13
|
0.06±0.18
|
− 0.15–0.04
|
0.260
|
DF=dominant foot; CI=confidence interval; AN=anterior; PM=posteromedial;
PL=posterolateral.
The relationship between the FAOS score and the isokinetic muscle strength of the
affected side was also examined. There was a significant correlation between evertor
peak torque and total work deficits at 30°/s (p=0.022), as well as the evertor peak
torque deficit at 120°/s (p=0.048) ([Table
3]). This suggests that functional impairment correlates with reduced
peroneal strength.
Table 3 Relationship between FAOS and the concentric
strength.
|
Measurements
|
|
|
r
|
p-value
|
|
Peak torque deficit (%)
|
Invertor
|
30º
|
− 0.231
|
0.137
|
|
120º
|
− 0.040
|
0.801
|
|
Evertor
|
30º
|
− 0.349
|
0.022
|
|
120º
|
− 0.259
|
0.094
|
|
Total work deficit (%)
|
Invertor
|
30º
|
− 0.236
|
0.128
|
|
120º
|
− 0.103
|
0.509
|
|
Evertor
|
30º
|
− 0.374
|
0.013
|
|
120º
|
− 0.303
|
0.048
|
|
Time to peak torque
|
Invertor
|
30º
|
− 0.140
|
0.370
|
|
120º
|
− 0.083
|
0.596
|
|
Evertor
|
30º
|
− 0.106
|
0.499
|
|
120º
|
− 0.077
|
0.622
|
Discussion
Our findings revealed that there were no significant differences in muscle strength
and balance between the DF and non-DF in individuals with CAI, contrary to the
expectation that the dominant limb, typically subjected to greater physical demands,
might exhibit greater strength and balance [3]
[4]. Therefore, it could be
interpreted that the muscle strength and balance of the DF were reduced compared
with those of the non-DF in individuals with CAI.
Interpreting the results is difficult as to whether the similarity in muscle strength
and balance on both sides is due to reduced overall physical activity levels
(resulting from discomfort in the affected ankle), or whether it is a consequence
of
reduced use of the affected side. The absence of significant differences in FAOS
between patients with CAI in the DF and non-DF groups could indicate an adaptation
to the chronic condition. Alternatively, it might be attributed to the increased use
of the non-DF when the DF is affected. The complex relationship between discomfort,
muscle strength, and balance in CAI requires further research.
To minimize statistical errors, our study only included patients with right-sided
DF.
The literature presents varying results regarding lower limb dominance and its
association with ankle sprains. While some studies suggest that lower limb dominance
is a risk factor for injury, particularly in high-demand activities [6]
[12], others show conflicting results [13]
[14]. We excluded patients with left-sided DF to address this
ambiguity.
Bilateral muscle strength deficit is a risk factor for CAI. It has been studied in
athletes [15] due to its role in injury
prevention and rehabilitation [8]. Eler
et al. found no difference in the ankle evertor and invertor muscle strength between
the dominant and nondominant limbs in their research of elite handball players [16]. In 1984, Wong et al. observed
symmetry in the ankle evertor and invertor muscle strength in both limbs of healthy
individuals [17]. However, similar
studies in nonathletes with CAI are lacking. Our findings indicate no discernible
difference in strength between the limbs.
CAI has been associated with peroneal muscle strength, suggesting that peroneal
muscle weakness may contribute to CAI development [18]. Arnold et al. reported that
decreased eversion strength is associated with impaired proprioception and
contributes to CAI development [19]. Our
study also found that peroneal muscle strength deficit was correlated with reduced
FAOS. Thus, evertor muscle strength is important in stabilizing the ankle and
preventing CAI, and evertor muscle strengthening exercises need to be included in
rehabilitation protocols.
This study had several limitations. First, only a small number of patients were
included. Therefore, it is difficult to generalize the results. However, the
significance of our study lies in analyzing the impact of dominant foot on ankle
instability from a different perspective compared to previous research. Second, this
was a retrospective study; thus, many patient factors were not adequately
controlled. We made extensive efforts to control those factors by applying broad
exclusion criteria and only including patients with right-sided DF. However, the
lack of information regarding the preexisting patient conditions and the different
conservative treatment periods and methods until the decision for surgery made it
difficult to take these variables into account. Future prospective studies with a
larger number of well-controlled participants are needed. Third, we did not include
the imaging results of the patients in the analysis. Functional instability and
patient discomfort play crucial roles in deciding the surgical treatment for CAI.
Although the relative importance of imaging can be diminished, it is still essential
to consider the effects of ligament damage and mechanical instability on strength
and proprioception.
Conclusion
In conclusion, no significant differences in muscle strength and balance were found
between the DF and non-DF in patients with CAI. Peroneal muscle strength deficit was
associated with functional impairment. Thus, peroneal muscle strengthening is
essential in CAI rehabilitation. When CAI affects the DF, a substantial decrease in
strength can be expected. Therefore, these findings should be considered in
conservative treatment approaches.
