Ankle sprain as a work-related accident: status of proprioception after 2 weeks

Study design

A descriptive, observational and transversal study was designed to study the differences in behaviour of the centre of pressure (CoP) and proprioception of healthy feet and feet that have undergone an ankle sprain, two weeks after this occurred. The period of 2 weeks was similar to that used in other studies (Evans, Hertel & Sebastianelli, 2004; Doherty et al., 2014; Leanderson et al., 1999; McKeon & Hertel, 2008a; Hertel, Buckley & Denegar, 2001). The present study has been carried out following the STROBE criteria.

Participants

Participants were employees of companies signed up to the mutual company XXXX who, due to a work-related accident, attended this mutual seeking medical treatment in Seville between February 2012 and June 2014. Therefore, they had to comply with the inclusion criteria and voluntarily agree to be included in the study. All participants gave written consent. The Experimentation Ethics Committee of the University of Seville approved the study.

Inclusion criteria were: being an active employee of working age (in Spain, aged between 18 and 65); having a medical diagnosis of grade 1 or 2 ankle sprain in just one ankle (Mann et al., 2002; Fong et al., 2009), of less than 2 weeks clinical course; not having undergone a sprain in the contralateral ankle or knees in the last 12 months; not suffering from disorders related to the vestibular system; not having undergone osteoarticular surgery of the ankle or subtalar joint or significant trauma that could have modified normal anatomy in these joints, or altered the sensory and motor pathways (Michelson & Hutchins, 1995); not presenting degenerative osteoarticular diseases and/or neuromuscular imbalances; and not taking sedative treatments of the vestibular system, antidepressants, anxiolytics or similar substances that delay or impair the sensory and motor system’s speed of response.

Procedure

The evaluation protocol was performed using a force plate Dinascan/IBV^® (Biomechanical Institute of Valencia, Valencia, Spain). Five tests were undertaken, one control and four effective, according to the protocol set out by the Biomechanical Institute of Valencia (BIV) (Asociación Instituo de Biomecánica de Valencia, 2017). The force plate had an active area of 600 × 370 mm, 100 mm height, 25 kg weight and a measurement range of vertical and horizontal strength of 4,500 N and + 750 N, respectively. It had a sampling frequency of up to 1,000 Hz. The force plate was embedded in a floorboard with a mechanical structure to house the platform measuring 3.5 × 1.5 m. The application NedRodilla/IBV^® (Biomechanical Institute of Valencia, Valencia, Spain) was used to analyse leg stability data form platform.

First, the bipodal Romberg’s test was performed on a 90 mm foam rubber with the eyes closed (BREC90 mm) to elucidate whether or not the participant had altered the vestibular system. If a positive outcome was obtained, the participant was excluded from the study. To perform this test a foam rubber 90 mm thick, 56.7 kg/m³ density and penetration resistance at 25% of 246 N, was used (Asociación Instituo de Biomecánica de Valencia, 2017; Baydal-Bertomeu et al., 2004). Once the foam rubber was placed on the force plate, the participant was asked to stood on it barefoot with arms extended along the body, looking straight ahead, focused on a fixed far away point and as quiet as possible. They were asked to close their eyes and then the 30-second test began. This was repeated three times.

The following tests were then performed:

• Unipedal Romberg’s test with eyes open (MREO): the participant was positioned with unipdeal weight bearing with the contralateral foot placed at half height the supporting leg (Fig. 1).

• Unipedal Romberg’s test with eyes open on a 30 mm thick foam rubber (MREO30mm): the participant stood in the same way as MREO, but on the force plate there was a 30 mm thick foam rubber, with the same size and shape as the platform.

• Unipedal Romberg’s test with eyes closed (MREC): same test as the MREO but with the eyes closed.

• Romberg’s test as unipedal weight bearing with eyes closed on a 30 mm thick foam rubber (MREC30 mm): same test as the MREO30 mm but with the eyes closed.

The test always began with the right foot and alternated with the left foot (as manufactured suggest), until three measurements were taken for each foot to use the mean of the three measurements during the statistical analysis. Participants had to look straight ahead at a fixed point and they could not speak for the 30 s each measurement lasted. The arms had to remain extended over the body without removing them to keep balanced and avoid contact of one leg with the other.

Measurements

Measurements were taken by means of the participants’ record of variations in CoP when they were on the force plate. The following records were obtained:

1. Area swept (mm²): this is the area swept by the CoP during the test.

2. 75th percentile speed (mm/s): determines the 75th speed percentile for foot correction to maintain balance.

3. Mediolateral movement (mm): evaluation of movement of the participant’s CoP along the mediolateral axis.

4. Anteroposterior movement (mm): evaluation of movement of the participant’s CoP along the anteroposterior axis.

5. Frequency of mediolateral oscillation (Hz): evaluates the characteristic frequency of the participant’s statokinesiogram signal along the mediolateral axis.

6. Frequency of anteroposterior oscillation (Hz): evaluates the characteristic frequency of the participant’s statokinesiogram signal along the anteroposterior axis.

7. Test time (%): represents the percentage total test duration time (15 s) that the participant was able to maintain balance without touching the floor with their contralateral foot.

8. MREO evaluation (%): determines a relative value obtained from the mean percentage values for all variables obtained during the tests performed with eyes open.

9. MREO30mm evaluation (%): determines a relative value obtained from the mean percentage values for all variables obtained during the tests performed on foam rubber with eyes open.

10. MREC evaluation (%): determines a relative value obtained from the mean percentage values for all variables obtained during the tests performed with eyes closed.

11. MREC30 mm evaluation (%): determines a relative value obtained from the mean percentage values for all variables obtained during the tests performed with foam rubber with eyes closed.

12. Final eyes open evaluation (EO) (%): determines a relative value obtained from the mean values of the variables “MREO Evaluation” and “MREO30mm Evaluation”.

13. Final eyes closed evaluation (EC) (%): determines a relative value obtained from the mean values of the variables “MREC Evaluation” and “MREC30 mm Evaluation”

During the four measurements, the value increases with balance disorders, age and difficulty of the test and in oscillation frequency tests the value reduces with balance disorders, age and test difficulty.

Measurements 1 to 6 were also expressed as a percentage after comparing the absolute value obtained with a gold standard database from healthy people (Baydal-Bertomeu et al., 2004). The database was validated by the BIV for all their equipment (Asociación Instituo de Biomecánica de Valencia, 2017). For all tests expressed as a percentage, the value decreases with balance disorders.

Sample size calculation

To calculate the sample size in this study, the overall final valuation of the tests with eyes open (EO)(%) was taken as a reference variable because this is a variable that all participants managed to complete because it was less demanding. Therefore, it was desirable that at least in the eyes open test healthy and injured individuals obtained a 95% and 65% score, respectively. This means it was being implicitly determined that the difference in minimal proportions that we wished to detect is worth the difference between both. ${\displaystyle P_{\mathrm{Healthy}}=0.95}$ ${\displaystyle P_{\mathrm{Injured}}=0.65}$ ${\displaystyle D=P_{\mathrm{Healthy}}-P_{\mathrm{Injured}}=0.3.}$ The mean proportion was calculated, P_M

The risk α was set at 5% bilateral, whereby Z_α∕2 is equal to 1.96. ${\displaystyle \alpha ∕2=0.025}$ ${\displaystyle Z_{\alpha ∕2}=1.96.}$ The risk β was determined to be 20%. Therefore, the power was 80% (1-β). ${\displaystyle \beta =0.2}$ ${\displaystyle Z_{\beta }=0.84.}$ The equation to apply for the calculation of sample size for each group was: ${\displaystyle n=\frac{2\cdot p_M\cdot q_M\cdot {\left(z_{\frac{\alpha }{2}}+z_{\beta }\right)}^2}{{\left(p_{\text{healthy}-}{p}_{\text{affected}}\right)}^2}=\frac{2\cdot 0.80\cdot 0.2\cdot {\left(1.96+0.84\right)}^2}{{\left(0.95-0.65\right)}^2}=27.88.}$ The calculation of sample size revealed that 28 feet were necessary in each group. Finally, 30 feet were included in each group.

Data analysis

Data were analysed with the software IBM SPSS Statistics 22^® (IBM, Armonk, NY, USA). Normality (Shapiro–Wilk) and randomness tests were performed to determine the use of parametric or nonparametric tests. Parametric tests (t-test for equality of means) were used when the data followed a normal distribution and they were random. Otherwise, the Mann–Whitney U test was used for independent samples. To ascertain the predictive level that could be attained from the condition of an ankle (injured or healthy), regression analysis was applied based on variables that had statistically significant differences. Subsequently, a multiple logistic regression model was performed for all variables that presented statistically significant differences. From the results of this regression model the COR curve test was performed to find a predictive cut-off point, and positive and negative predictive values were calculated.