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Abstract

Background:

The question whether or not a patient with a hip brace should drive a car is of obvious importance because the advice given to patients to resume driving is often anecdotal as few scientific data are available on this specific subject.

Objectives:

To assess driving ability (brake response time) with commonly used hip braces.

Study design:

Repeated measures design.

Methods:

Brake response time was assessed under six conditions: (1) without a brace (control), (2) with a typical postoperative hip brace with adjustable range of motion and the settings: unrestricted, (3) flexion limited to 70°, (4) extension blocked at 20° hip flexion, (5) both flexion and extension limited (20°/70°) and (6) an elastic hip bandage. Brake response time was assessed using a custom-made driving simulator as used in previous studies. The participants were a convenience sample of able-bodied participants.

Results:

A total of 70 participants (35 women and 35 men) participated in our study. Mean age was 31.1 (standard deviation: 10.6; range: 21.7–66.4) years. A significant within-subject effect for brake response time was found (p = 0.009), but subsequent post hoc analyses revealed no significant differences between control and the other settings.

Conclusion:

Based on our findings, it does not seem mandatory to recommend driving abstinence for patients wearing a hip orthosis. We suggest that our results be interpreted with caution, because (1) an underlying pathological hip condition needs to be considered, (2) the ability to drive a car safely is multifactorial and brake response time is only one component thereof and (3) brake response time measurements were performed only with healthy participants.

Clinical relevance

Hip braces are used in the context of joint-preserving and prosthetic surgery of the hip. Therefore, clinicians are confronted with the question whether to allow driving a car with the respective hip brace or not. Our data suggest that hip braces do not impair brake response time.

Keywords

Driving performance brake response time hip brace driving safety limb orthotic orthotic

Background

Hip braces are used in the context of joint-preserving and prosthetic surgery of the hip.^1–3 Therefore, clinicians are confronted with the question whether to allow driving a car with the respective hip brace or not. When patients are temporarily unable to drive a car, they lose their independence and quality of life, which may have serious social and economic consequences for them. The advice given to such patients to resume car driving is often anecdotal as few scientific data are available on this specific subject.

Of the various factors that constitute driving performance, brake response time (BRT) is considered one of the most important factors responsible for driving safety.⁴ Very few experimental studies have looked at BRT during orthopaedic immobilization of the right lower limb.^5–7 Tremblay et al.⁷ investigated BRT during immobilization of the right leg with an ankle orthosis and a walking cast. Dammerer et al.⁵ and Waton et al.⁶ have studied immobilization of the right knee. When using a knee brace, impaired BRT was found only for those braces that restrict range of motion, whereas several other types of knee braces were not found to have a negative effect on driving.⁵ However, to the best of our knowledge, there is only one study assessing the effect of hip braces on BRT.⁸ Hofmann et al.⁸ found in their study that foot transfer time is prolonged with the use of hip orthosis, indicating impairment in driving performance. However, the clinical relevance of the small changes observed in BRT can be discussed.

Apart from the issue of braces, numerous studies investigated driving ability in the context of orthopaedic surgical procedures^9–15 and recommended driving abstinence of 1 week (knee arthroscopy)¹⁶ to 8 weeks postoperatively (total hip arthroplasty).¹¹

Due to the lack of evidence, we aimed to analyse the effect of different hip braces on BRT. For this purpose, it was hypothesized that BRT would show statistically significant differences among the several types of hip braces and an unrestricted control run.

Methods

The local university ethics committee approved the study protocol, and written informed consent was obtained from all subjects before participation. The study is registered in two public trial registries.

A total of 70 participants were enrolled in this study. They were recruited from among the investigators’ acquaintances. We recruited 50% men and 50% women and attempted to include subjects of all ages. Inclusion and exclusion criteria were as described in a previous study.⁵ To be included in the study, participants must have had a valid driver’s license, used the right foot exclusively for accelerating and braking and have been free of any medical condition that could impair their ability to drive. Excluded were volunteers who were taking medication that could affect reaction time (e.g. benzodiazepines and over-the-counter allergy and cold medications) or had a history of alcohol or drug abuse, central nervous system disorder such as epilepsy, psychiatric disorder or musculoskeletal disease, as well as participants with any recent (previous 3 months) surgery on the right lower limb or any visual acuity disorder.

Applying a repeated measures design, BRT was measured as described in previous literature.^5,9,10,15,17 The custom-built car simulator consisted of an adjustable car seat fixed on a frame with three hanging pedals (accelerator, clutch and brake) (Figure 1(a)). The seat was adjustable for seat inclination, head rest and seat-pedal distance to simulate the patient’s favourite driving position.^15,18 Positioned at a constant distance in front of the patient were a red and a green signal light (Figure 1(b)). The measurement sequence started when the patient suppressed the accelerator pedal fully and the green light lit up. After an interval of 5–30 s (investigator’s discretion), the investigator pressed an external trigger, invisible to the patient, which activated the red signal light and the electronic clock. The participants were instructed to suppress the brake pedal as quickly as possible with the right foot when the red signal appeared. The time interval (measured in milliseconds) between the time when the red signal was switched on and the brake pedal was suppressed was registered. BRT was measured 10 times for each hip brace with an interval of 5–10 s between measurements. The average of the 10 measurements was taken as BRT.

Figure 1.

(a) Custom-made apparatus for measurement of brake reaction time (BRT). Pedals from left to right: clutch (coupler); brake; accelerator; (b) External unit: large (red) light (visual stimulus initiating the braking procedure); small (green) light (indicating that the accelerator is fully suppressed – subject not in a ‘ready-to-brake’ position).

All participants were given the same standardized instructions. All tests were performed exclusively with the right leg. Each participant performed three trial runs to familiarize himself with the brace before starting the experiment.

BRT was assessed under the following six conditions: (1) without a brace (control), (2) with a postoperative hip brace with adjustable range of motion (Newport^® 3/4; Donjoy, Inc., Vista, CA, USA) and the settings: unrestricted (Hip ROM unrestricted), (3) flexion limited to 70° (Hip ROM 70), (4) extension blocked at 20° hip flexion (Hip ROM 20), (5) both flexion and extension limited (20°/70°) (Hip ROM 2070) and (6) an elastic hip bandage (EFO; Teufel GmbH, Wangen, Germany) (elastic hip support). Fixation of the hip braces was standardized and always performed by the same investigator. The order of the measuring sequence was randomized to counteract a possible learning effect (crossover design). Randomization was performed with an Internet-based randomizer provided by the Department of Medical Statistics and Informatics of a medical university.¹⁹

A sample size calculation was performed with G*Power 3.1 (Heinrich Heine University Duesseldorf, Germany, 2015). For that analysis, we expected a small effect size (f = 0.10), a small to medium correlation between repeated measures (0.5) with an alpha of 0.05 and six measurements. Aiming for a power of 0.95, we calculated a sample size of around 75. We chose a sample size large enough to detect even effects of small sizes with a high power in order to minimize the probability of type II errors.

Statistical analysis of the impact of the various types of brace on reaction time was performed with the help of an analysis of variance (ANOVA) for repeated measurements with the various brace types and settings.

To test for the sphericity assumption, Mauchly’s test for sphericity was performed and an appropriate epsilon correction was applied to calculate the overall significance. Pair-wise comparisons of the braces were calculated with least significant differences (LSD). For this reason, no correction for alpha-inflation was applied, resulting in a family-wise error rate of approximately p = 0.54, based on our assumed alpha of p ⩽ 0.05. Available procedures like Bonferroni or Sidak would have greatly reduced the power of the analysis, which was not our intention as not detecting a significant difference is in this scenario worse than a false-positive. Before the ANOVA, all reaction time variables were tested for normal distribution using the Kolmogorov–Smirnov test (with adjusted alpha to compensate for the lower power of that test). Since normal distribution could not be assumed according to the test and a positive skewness for all variables was found, a log-transformation (ln) was performed to obtain normal distribution and satisfy this ANOVA requirement. In addition, we calculated the proportions of patients below and above a BRT threshold of 700 ms. The threshold of 700 ms was chosen because several road authorities recommend absolute maximum BRT values between 700 and 1500 ms;^20–22 we selected the most conservative value. For the statistical tests, p-values of 0.05 or lower were considered statistically significant. All statistical analyses were conducted with SPSS 20 (IBM Corporation, Armonk, NY, USA).

Results

The participants’ sociodemographic characteristics and driving experience are presented in Table 1. A total of 70 volunteers (35 women and 35 men) were included in this study. Two participants were excluded before study commencement (one did not have a valid driving license and one felt pain in his right ankle during the test). The mean age was 31.1 (standard deviation (SD): 10.6; range: 21.7–66.4) years.

Table 1.

Sociodemographic characteristics and driving experience (N = 70; 35 women and 35 men).

	Mean	SD	Range
Age (years)	31.1	10.6	21.7–66.4
Years of driving experience	12.6	10.1	1.1–45.5
Driving hours per week	3.4	2.4	1–10
Distance travelled (km/year)	12,133	10,382	20–60,000

SD: standard deviation.

The repeated measures ANOVA showed a significant within-subject effect for the braces (p = 0.009, epsilon correction of 0.802 due to a highly significant result when applying Mauchly’s test for sphericity). The observed power of the within-subject effect was 0.854.

BRT was not found to be significantly impaired for any of the orthoses investigated as compared to the control group. All significant differences, indicated by the result of the within-subject effects, were found between the five brace settings.

Mean BRT was 558 ms (SD: 123) for the control group, 543 ms (SD: 85) for the unrestricted orthosis (p = 0.353), 559 ms (SD: 79) for the orthosis with flexion limited to 70° (p = 0.595), 581 ms (SD: 116) for the orthosis with extension blocked at 20° hip flexion (p = 0.052), 559 ms (SD: 81) for the orthosis with both flexion and extension blocked (p = 0.616) and 543 ms (SD: 85) for the elastic hip bandage (p = 0.324).

Table 2 shows the number and proportion of participants with BRT less than and greater than the 700 ms threshold. BRT for each test condition is shown in Table 3 and Figure 2. All investigated hip braces are shown in Figure 3.

Table 2.

Proportion of patients above or below the threshold of 700 ms BRT.

Type of hip brace	Frequency (n)		Percent
	<700 ms	>700 ms	<700 ms	>700 ms
None (control run)	65	5	92.9	7.1
Elastic hip support	68	2	97.1	2.9
Hip ROM unrestricted	66	4	94.3	5.7
Hip ROM 20	61	9	87.1	12.9
Hip ROM 70	67	3	95.7	4.3
Hip ROM 2070	67	3	95.7	4.3

Table 3.

Brake reaction time measured in milliseconds with the various braces, as compared to the control run.

Type of hip brace	Mean	SD	95% CI	p-values; comparison with no brace
None (control run)	558.2	123.1	528.9–587.6	–
Elastic hip support	543.2	85.9	522.8–563.8	0.324
Hip ROM unrestricted	543.4	85.3	523.1–563.8	0.353
Hip ROM 20	581.6	116.1	554.0–609.3	0.052
Hip ROM 70	559.3	79.0	540.5–578.2	0.595
Hip ROM 2070	559.1	81.3	559.7–578.5	0.616

SD: standard deviation; CI: confidence interval.

Figure 2.

Diagram BRT versus braces. Brake response time with the different orthoses, as compared to the control run.

Figure 3.

Investigated hip braces (a) elastic hip support (EFO^TM; Wilhelm Julius Teufel GmbH, Wangen, Germany) and (b) postoperative hip brace with adjustable range of motion (Newport^® 3/4; Donjoy, Inc., Vista, CA, USA).

Discussion

The most important finding is that using any of the hip braces tested did not significantly impair BRT. Therefore, it could be argued not to recommend driving abstinence for patients wearing hip braces. However, our findings should be interpreted with caution. First, we tested only healthy subjects and an additional underlying specific hip pathology could impair BRT. Second, a statistical trend was observed with the hip brace with extension blocked at 20° flexion (p = 0.052). It could be that this result is affected by a type-2 error. Third, the ability to drive a car safely is considered to be multifactorial, and BRT is the only one of several important factors that should be considered.^4,13,18

The issue of hip braces and driving ability is of high clinical relevance, because hip braces are used by many surgeons in varying conservative and postoperative settings.^1–3,23 Kelly et al.¹ use hip braces during the day for 10 days to 2 weeks after arthroscopic labral repair in the hip to limit hip motion and particularly give flexion control and abduction position. In the case of a proximal femoral replacement, Manoso et al.²³ recommended a brace for 3–4 months postoperatively. To the best of our knowledge, our study is the second study to investigate the effect of hip braces on BRT. Hofmann et al.⁸ investigated the effect of hip and spine orthoses on braking parameters. They concluded that wearing a hip or spine orthosis does not preclude driving a car per se, but recommended that the underlying pathological condition be considered.⁸ Our results are well in line with their findings.

Excluding a patient from driving for an unnecessarily long period may have substantial social and economic consequences. Equally important, advising a patient to return to driving prematurely is potentially dangerous and may make the surgeon vulnerable to litigation should the patient be involved in an accident while driving.²⁴

Moreover, relatively small changes in emergency braking time can be important.²⁴ For example, if a car is driving 40 mi/h (64 km/h), it covers approximately 60 ft/s (18 m/s).²⁴ A 100-ms increase in emergency braking time would mean that the car must travel an additional 6 ft (1.8 m) before coming to a complete stop.²⁴ It could be speculated that there might be a specific amount of BRT increase that would lead to a greater accident likelihood. However, to our best knowledge, there is no evidence to quantify the relation between BRT increase and accident risk. We performed a literature search and found no studies on the relation between impaired BRT, on one hand, and accident risk, on the other hand. We recommend that future studies be performed on this specific issue.⁵

It might be argued that we compared only the different braces with an unrestricted control run, instead of using an absolute BRT limit. The threshold of 700 ms was chosen, because a number of road authorities recommend absolute maximum BRT values of 700 and 1500 ms.^20–22 We selected the most conservative value. Our findings show no statistically significant increase in BRT for any investigated hip orthosis. This was supported by our additional analysis concerning the absolute threshold of 700 ms. The proportion of subjects with BRT below/above the threshold of 700 ms did not differ between the groups. These results are shown in Table 2.

Reaction time is deemed a complex task^25–27 and braking involves a complex interaction between ankle dorsal and plantar flexion, hip internal and external rotation, and subtle hip and knee flexion and extension.²⁸ It includes different psychomotor processes and is defined as the amount of time an individual takes to respond and complete a movement after a stimulus has been presented.^25–27 In our study, BRT was defined as the amount of time it took for the participant to move his or her right foot from the accelerator to the brake pedal after the red light appeared on the driving simulator and did not distinguish among thinking time, movement time and brake travel time, as in a previous study.⁶ Moreover, in previous studies, BRT has been described as a wide range and variety of results that vary under specific conditions.²⁹ Green reported that a braking process can vary ±0.75 s depending on whether it is anticipated or not.²⁹ During our BRT measurements, we attempted to minimize the effect of participant expectation by having the participant listen to music, by talking with the participant and asking him questions as well as by having the investigator be out of the patient’s line of sight when pushing the external trigger to activate the red signal light and the electronic clock. However, we agree with Holt et al.²⁴ and feel such precautions do not recreate the element of surprise that occurs when an unexpected danger presents itself during the actual driving experience, and this factor cannot be fully addressed in such a BRT measurement experiment conducted in healthy volunteers.

Our study is the second to test driving ability with hip braces. The main strengths of our study are the large number of participants, the standardized method, the randomized measuring sequence and the five different brace situations tested. As a limitation of our study, we acknowledge that we did not investigate the combined effect of a specific hip pathology and a particular hip brace. We analysed only the isolated effect of hip braces in healthy participants. We are aware of the fact that many braced patients have undergone complex hip surgery or have suffered a recent traumatic dislocation and are on protected weight bearing, for example, 50% partial weight bearing using walkers or crutches. This might limit breaking response time as well. The BRT in this patient group would likely have additional confounding variables likely to impair their response. These subjects would not be entirely comparable to the control group used in our study. This study does not measure the impact of a surgical procedure or joint pathology. We analysed only the isolated effect of hip braces in healthy participants. Furthermore, the external trigger was depressed at the investigator’s discretion and not at a random time. This may produce a bias, because the same investigator talked to the participant during testing. Triggering the red light randomly versus at the researcher’s discretion would eliminate this bias.

We believe that future studies should also include the combination of specific hip pathologies and the effect of wearing a hip brace.

Conclusion

In conclusion, based on our findings, it does not seem mandatory to recommend driving abstinence for patients wearing a hip orthosis. We suggest that our results be interpreted with caution, because (1) an underlying pathological hip condition needs to be considered, (2) the ability to drive a car safely is multifactorial and BRT is the only one component thereof and (3) BRT measurements were performed only with healthy participants.

Footnotes

Ethical approval

Author contribution

DD conceived the study, drafted the manuscript, and performed the study registration and statistical analysis. CW collected the data, participated in the study coordination, and helped draft the manuscript. DH drafted the figures, proofread the manuscript and revised the manuscript substantially, participated in the data processing, and performed the statistical analysis. CH assisted by proofreading the manuscript, and revised the manuscript substantially. MK assisted by proofreading the manuscript and revised the manuscript substantially. LM helped draft the manuscript, proofread the manuscript, and revised the manuscript substantially. All authors read and approved the final manuscript.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship and/or publication of this article.

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Effect of hip braces on brake response time: Repeated measures designed study

Abstract

Background:

Objectives:

Study design:

Methods:

Results:

Conclusion:

Clinical relevance

Keywords

Background

Methods

Results

Discussion

Conclusion

Footnotes

Ethical approval

Author contribution

Declaration of conflicting interests

Funding

References