| | Driving Pedal Reaction Times After Right Transtibial AmputationsAbstract Meikle B, Devlin M, Pauley T. Driving pedal reaction times after right transtibial amputations. ObjectivesTo determine if right transtibial amputees have the potential to safely operate the foot pedals of a vehicle with their prosthetic foot, and to determine which of 4 driving techniques is associated with the fastest reaction times. SettingOutpatient amputee clinic. ParticipantsTen subjects with right-sided, transtibial amputations. InterventionBrake pedal response times were measured using 4 different driving techniques: right-sided accelerator with (1) prosthesis operating both the accelerator and brake pedals, (2) prosthesis operating the accelerator and left foot operating the brake, (3) left foot operating both the accelerator and brake, and (4) left-sided accelerator with the left foot operating both the accelerator and brake. Main Outcome MeasuresReaction time, movement time, total response time, and pedal configuration preference. ResultsTotal response times were slowest using a 2-footed driving technique (P<.001). Total response times were comparable using a left-sided accelerator versus the prosthesis. Using the left foot to operate both the accelerator and brake in a conventional right-footed accelerator design led to the fastest reaction (P<.001) and total response times (P<.01), although it is unclear if this is a realistic driving technique for all amputees. ConclusionsOur results suggest that right transtibial amputees should be instructed not to drive with a 2-footed technique, and that they have similar pedal response times using their prosthesis when compared with a left-sided accelerator.
AFTER LOWER-EXTREMITY AMPUTATION, amputees often have difficulties returning to their previous activity levels and in returning to work.1 The ability to drive a vehicle is a major step toward restoring functional independence and making it possible for a person to return to their usual social and work-related activities.2
It is generally accepted that left lower-extremity amputees should not have any amputation-related difficulties driving a vehicle, provided that the vehicle has an automatic transmission. However, a right lower-extremity amputation would be expected to have a much greater effect on a person’s driving ability.
Driving ability of amputees has received very little attention in the scientific literature. Studies that have investigated driving in this population have been limited to investigations of assistive devices for upper-extremity amputees,3, 4 the driving performances of people with juvenile onset amputations,5 or the tendency of amputees to use automobiles versus other forms of transportation.6 It appears that the mechanics of driving ability in amputees has not been studied. As a result, there is no evidence available with which to counsel right transtibial amputees resuming driving. It is unclear what vehicle modifications are required (if any), which foot should operate the pedals, and whether those amputees can safely operate a manual transmission vehicle.
Our objective in this study was to measure the brake pedal reaction times of right transtibial amputees when using several different techniques of operating the foot pedals. This study was a preliminary investigation intended to answer the following 2 questions: Do right transtibial amputees have the potential to safely operate vehicle foot pedals with their prosthesis? Which technique for operating the foot pedals is associated with the fastest reaction times?
Methods  Design We used a repeated-measures design that repeatedly tested participants’ reaction, movement, and response times across 4 different pedal configurations during a single session; the sequence of the configurations was randomly allocated. Subject Selection We screened a convenience sample of amputees attending an outpatient amputee clinic for study inclusion. Subjects were eligible for the study if they had undergone a traumatic- or tumor- or vascular- (without diabetes mellitus) related right transtibial amputation, were licensed to drive prior to amputation, and were at least 6 months post initial prosthetic fitting (to ensure adequate familiarity with prosthesis). Apparatus The apparatus included a set of brake and accelerator pedalsa used in combination with reaction timer software.b The pedals were oriented in such a way as to replicate their positions relative to the seat in a conventional automobile. Pedal configuration could be manipulated to simulate a left-sided accelerator. Distance from the seat to the pedals could be adjusted to personal preference to allow for patients of differing stature. The subject viewed the stimulus on a computer monitor placed approximately 1m away. Prior to onset of the stimulus, the subject would simply see 2 larger gray circles on the screen ahead. When the circles turned solid red, the required reaction was to move the foot from the accelerator to the brake, which is the usual reaction to a red light in real traffic. Procedures Each subject used their own prosthesis during the study. Foot-pedal reaction time was tested with 4 different techniques for operating the foot pedals:
1.Right-sided accelerator, using the prosthesis to operate both the accelerator and brake.
2.Right-sided accelerator, using the prosthesis to operate the accelerator and the left foot to operate the brake.
3.Right-sided accelerator, using the left foot to operate both the accelerator and brake.
4.Left-sided accelerator, using the left foot to operate both the accelerator and brake.
Subjects were told to fully depress the accelerator pedal at the beginning of each trial. A visual stimulus signaled the subject to release the accelerator and depress the brake. Reaction time was measured from the onset of the stimulus to when the subject’s foot began to release the accelerator pedal. Movement time was measured from the time the subject began to release the accelerator pedal to when the subject’s foot had fully depressed the brake pedal. Response time was the sum of reaction time and movement time. The different pedal layouts and techniques were tested in random order. For each different technique, subjects were given 4 practice trials followed by 18 test trials. Each trial was performed 15 to 30 seconds apart, and approximately a 1-minute rest was given prior to testing with the different techniques. After testing, each subject was asked to rank driving techniques in order of preference. To avoid subject bias, they were blinded to reaction time results until they had reported their preference. This study was approved by the West Park Healthcare Centre Research Ethics Committee. Outcome Measures The primary outcome measure was total brake pedal response time (in milliseconds), as measured by a combination of reaction time and movement time. The secondary outcome measure was subject preference. Analysis We used descriptive statistics to summarize the data. Repeated-measures analysis of variance (ANOVA) was used to test for statistically significant differences between reaction time, movement time, and total response time across the 4 pedal arrangement conditions. Where significant differences were found, comparisons between paired pedal conditions were made using repeated t tests. We used the Holm’s sequential Bonferroni adjustment to control family-wise error rate across the 6 pairwise comparisons. It is not uncommon for right-sided amputees to switch to left-footed operation of the accelerator, therefore a subgroup analysis was performed among current drivers to compare braking times of those opting for right-footed accelerator operation versus those who used their left foot. A similar comparison was made between those who opted for right-footed brake operation versus those who used their left foot. Finally, we conducted a Friedman test to compare subject preferences for the various foot-pedal arrangements. The Wilcoxon signed-rank test was used to conduct follow-up pairwise comparisons. Results Table 1 summarizes subject demographics, driving information, and pedal arrangements before and after amputation. We conducted 3, 1-way repeated-measures ANOVAs to compare reaction time, movement time, and total response time across the 4 pedal conditions; their means and standard deviations (SDs) are presented in figure 1. Outliers were excluded from the analysis if they were greater than 3 SDs from the group mean. This resulted in 3.5% (6.3/180) of the data points, on average, being excluded from each of the 4 pedal conditions. ANOVA results revealed significant pedal condition effects for reaction time (Wilks λ=.42, F3,163=75.46, P<.001), movement time (Wilks λ=.70, F3,160=23.37, P<.001), and total response time (Wilks λ=.49, F3,157=54.89, P<.001). Follow-up pairwise comparisons were conducted for each time variable using paired-samples t tests. The Bonferroni adjustment was used to control family-wise error rate across the 6 pairwise comparisons required for the 4 levels of pedal condition within each time variable. Reaction Time The longest reaction times (from onset of stimulus to beginning of foot movement) were recorded when subjects operated the accelerator with their prosthetic foot and the brake with their left foot. This method of foot-pedal operation resulted in reaction times that were significantly longer than each of the other 3 pedal conditions (P<.001 for all 3 comparisons). In contrast, using the left foot to operate both the accelerator and brake when the pedals were arranged in a conventional right-footed accelerator design resulted in shorter reaction times than the times for each of the other 3 conditions (all 3 comparisons P<.001). There was no difference in reaction time between using the prosthetic foot to operate both pedals in the right-sided accelerator condition versus using the left foot to operate both pedals in the left-sided accelerator condition (P=.07). Movement Time As with reaction time, the longest movement times (from beginning of foot movement until brake is fully depressed) were observed when the subjects operated the accelerator with their prosthetic foot and the brake with their left foot. This method of foot-pedal operation resulted in movement times that were significantly longer than those in each of the other 3 conditions (all 3 comparisons P<.001). Movement times among the other 3 pedal conditions did not differ significantly. Total Response Time Pairwise comparisons of total response times resulted in much the same outcome as in the comparisons of reaction times across the 4 pedal conditions. The longest total response times (from onset of stimulus until brake is fully depressed) were observed when the subjects operated the accelerator with their prosthetic foot and the brake with their left foot (all 3 comparisons P<.001). Again, using the left foot to operate both the accelerator and brake when the pedals were arranged in a conventional right-footed accelerator design resulted in total response times that were of shorter duration than each of the other 3 conditions (all 3 comparisons P<.01). There was no difference in response times when the prosthetic foot was used to operate both pedals in the right-sided accelerator condition versus using the left foot to operate both pedals in the left-sided accelerator condition (P=.33). Usual Driving Technique We did a subgroup analysis to compare the braking times of 5 subjects who continued to drive postamputation. All 5 used their right foot to operate the accelerator and brake before amputation; 3 continued to use their right foot after amputation and 2 switched to a left-foot operation for the accelerator. Two continued to use their right foot for the brake, while 3 began using their left foot. A 2-way repeated-measures ANOVA with 1 within-subjects factor (4 levels of pedal arrangement) and 1 between-subjects factor (right- vs left-foot operated accelerator) was conducted for reaction, movement, and total response time to evaluate whether current pedal operation affects timing of responses. ANOVA revealed significant main effects for choice of foot operating the accelerator for reaction time (F1,81=76.14, P<.001), movement time (F1,83=49.54, P<.001), and total response time (F1,81=73.02, P<.001). ANOVA revealed significant main effects for choice of foot operating the brake for reaction time (F1,81=19.14, P<.001), movement time (F1,83=4.21, P<.05), and total response time (F1,81=8.79, P<.01). We used 1-way ANOVA to conduct follow-up pairwise comparisons between the left- and right-foot choices for each of the 4 pedal conditions. The Bonferroni adjustment was used to control family-wise error rate across the 4 pairwise comparisons required for the 4 levels of pedal condition within each foot choice. For reaction time, subjects who were currently using the right foot to operate the accelerator had consistently faster times for all pedal conditions than did those who had switched to the left foot to operate the accelerator. On average, right-footed accelerator users had reaction times that were 35 to 135ms faster than left-footed accelerator users (all P<.05). The same trend was observed for movement time and total response time. On average, right-footed accelerator users had movement times that were 87 to 134ms faster than left-footed accelerator users across all 4 pedal conditions (all P<.001). On average, right-footed accelerator users had total response times that were 163 to 275ms faster than left-footed accelerator users across all 4 pedal conditions (all P<.001). We conducted similar follow-up comparisons to compare right- and left-footed brake users. For reaction time, subjects using the right foot to operate the brake had consistently faster times for all pedal conditions than those subjects who had switched to the left foot to operate the brake. The differences, however, were only significant for the right-sided accelerator condition when the prosthetic leg was used to operate the accelerator and brake, as well as in the left-sided accelerator condition when the left leg was used. For these 2 conditions, right-footed brake users were 56 to 87ms faster (all P<.001). The same trends were found for movement time and total response time. On average, right-footed brake users had movement times that were 68 to 87ms faster than left-footed brake users across the same 2 pedal conditions (all P<.05). Likewise, on average, right-footed brake users had total response times that were 114 to 174ms faster than left-footed brake users across the same 2 pedal conditions (all P<.001). Experimental Pedal Preference Subjects were asked to rank each pedal arrangement in order of their own preference, with a rank of 1 indicating the most preferred arrangement and 4 indicating the least preferred. Figure 2 shows the distribution of ranks among the 4 conditions. Results of a Friedman test conducted to compare subject preferences for the various foot-pedal arrangements were significant (χ3,N=102 test = 9.00, P<.05), and the Kendal coefficient of concordance of .30 indicated fairly strong differences among the 4 pedal conditions. Follow-up pairwise comparisons between each of the 4 pedal conditions were conducted using a Wilcoxon signed-rank test. The Fisher least significant differences procedure was used to control type I errors at the .05 level across all comparisons. The only significant pairwise comparison was between the left-footed accelerator with the left foot operating the gas and brake and the right-footed accelerator with the prosthetic foot operating the gas and the left foot operating the brake (mean rank, 1.70 vs 3.40; P<.05). Also significant was the comparison between using the right-footed accelerator with the left foot operating the gas and brake and the right-footed accelerator with the prosthetic foot operating the gas and the left foot operating the brake (mean rank, 2.30 vs 3.40; P<.05). Stopping Distance Table 2 displays the effects of pedal condition when beginning to stop. Each cell in the table displays the distance covered in meters from the initiation of the stimulus until the time the brake is fully depressed at various velocities across all 4 pedal conditions. At 100kph (62mph), the subject would begin stopping his/her vehicle after traveling a distance of 28.5m after onset of the stimulus if he/she were using a right-footed accelerator with the left foot operating both the accelerator and brake. In contrast, if a subject was using a right-footed accelerator with the prosthetic foot operating the accelerator and left foot operating the brake, the vehicle would cover a distance of 36.7m prior to actuation of the brake, for a difference of 8.2m or roughly 2 car lengths. Discussion Restoring driving ability is a major achievement in the rehabilitation of traumatic lower-extremity amputees because it gives the amputee increased mobility and freedom; it is often necessary in order for the person to return to work. Although it is generally accepted that people with right-leg amputations can resume driving, we are unaware of any research that has investigated the safest technique for right lower-limb amputees to use to operate a vehicle’s foot pedals. Some experts have recommended that all right lower-extremity amputees have their vehicles modified to incorporate either left-foot accelerators or hand controls.7 This study was performed in a controlled setting and its results do not necessarily translate directly to real traffic situations. However, they do suggest that right lower-extremity amputees should be advised against using a 2-footed driving technique because that technique resulted in slower reaction times, slower movement times, and slower total response times than did any of the single-footed techniques. (While there were some statistically significant differences between various single-footed techniques, they do not appear to be of clinical significance.) Within single-footed techniques, there was no significant difference in response times between the prosthetic foot operating standard pedals and the left foot operating pedals with a left-sided accelerator. Therefore, our results suggest that right transtibial amputees have the potential to operate a conventional pedal arrangement using their prosthesis with comparable speed to the alternative of using a left-footed accelerator pedal with their left foot. Studies that have assessed brake response times of nondisabled drivers have shown large variations in response times, which can be accounted for by the differences between testing protocols. Measured response times are significantly affected by factors such as whether a stimulus to brake was anticipated, whether a driving simulator was used and, if so, what type was it, whether the response time was measured to initial pedal movement or complete pedal depression, and what type of stimulus to brake was used. Therefore, it is not appropriate to directly compare results from this study to results from any previous studies. However, we would note that studies that used methodology most similar to that of this study have generally shown mean total response times of approximately 700 to 750ms, and that brake response times slow by approximately 100 to 300ms with increased age.8 It remains unclear whether a left-sided accelerator should be routinely provided for amputees who drive with their left foot after amputation. In this study, the response times were actually slightly improved with the left foot operation of a right-sided accelerator as compared with the left-sided accelerator, however, subjects tended to prefer to use a left-sided accelerator. In addition, we did not investigate the possibility that some types of automobiles may not provide enough room for the left foot to operate the right-sided accelerator without obstruction from the (unused) prosthetic right foot. As a result, this study does not provide adequate evidence to support or oppose the use of a left-sided accelerator. Given the small sample size, brief duration of testing, lack of real driving situations, lack of testing of pedal pressure control, and the artificial nature of the testing apparatus, our results cannot be used to make specific recommendations regarding all amputees. It is recommended that amputees be assessed on an individual basis and recommendations be made based on each amputee’s specific circumstances. However, our results suggest that many right transtibial amputees do have the potential to safely operate a vehicle with their prosthesis, and a universal ban on driving with a prosthetic foot is not currently warranted. Further research is recommended in order to develop consensus recommendations regarding return to driving posttranstibial amputation, and to develop evidence-based recommendations for amputees with other levels of amputation. Conclusions Our results suggest that right transtibial amputees should be instructed not to drive with a 2-footed technique. Also, our results suggest that they have similar pedal response times when using their prosthesis in a traditional pedal arrangement as compared with using their intact left foot on a left-sided accelerator setup. Further research is recommended so that clear guidelines can be developed regarding a person’s return to driving recommendations after transtibial amputation. Suppliers
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a Division of Physiatry, Department of Medicine, University of Toronto, Toronto, ON, Canada b Clinical Evaluation and Research Unit, WestPark Healthcare Centre, Toronto, ON, Canada c Department of Medicine, Grey Bruce Health Services, Owen Sound, ON, Canada  Correspondence to Tim Pauley, MSc, WestPark Healthcare Centre, 82 Buttonwood Ave, Toronto, ON, M6M 2J5, Canada. Reprints are not available from the author.
Supported by a research grant provided by the Workplace Safety & Insurance Board (Ontario). No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. PII: S0003-9993(05)01374-2 doi:10.1016/j.apmr.2005.11.001 © 2006 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation. Published by Elsevier Inc. All rights reserved. | |
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