- Email: [email protected]
Driving reaction time before and after surgery for disc herniation in patients with preoperative paresis
The Spine Journal
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(2013)
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Clinical Study
Driving reaction time before and after surgery for disc herniation in patients with preoperative paresis Martin Thaler, MDa,*, Ricarda Lechner, MDa, Bernhard Foedinger, MDa, Christian Haid, PhDa, Pujan Kavakebi, MDb, Klaus Galiano, MDb, Alois Obwegeser, MDb a
Department of Orthopaedic Surgery, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria b Department of Neurosurgery, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria Received 7 June 2012; revised 28 March 2013; accepted 15 June 2013
Abstract
BACKGROUND CONTEXT: The effect of many types of surgeries on driving reaction time (DRT) has been reported. Although lumbar disc herniation is one of the most common spinal diseases, the effect on DRT has not been investigated. PURPOSE: To assess the effect of left- and right-sided pareses caused by lumbar disc herniation on DRT before and after surgery. STUDY DESIGN: Controlled prospective clinical trial. PATIENT SAMPLE: Patients undergoing disc surgery. OUTCOME MEASURES: Impact of paresis caused by lumbar disc herniation and disc surgery on DRT. METHODS: Forty-two consecutive patients (mean age, 50.3 years) were tested for DRT 1 day before surgery, postoperatively before hospital discharge, and 5 weeks after surgery. Visual analogue scale (VAS) for back and leg pain as well as pain medication and patients’ driving frequency were recorded. RESULTS: Significant improvement of DRT after surgery was seen in patients with left- and rightsided pareses (p!.005). For the right-sided paresis group, the preoperative DRT was 761 ms (median, interquartile range [IQR]: 490), 711 ms (median, IQR: 210) immediately postoperatively, and 645 ms (median, IQR: 150) at follow-up (FU). For the left-sided paresis group, DRT was 651 ms (median, IQR: 270) preoperatively, 592 ms (median, IQR: 260) postoperatively, and 569 ms (median, IQR: 140) at FU. Significant differences between right- and left-sided pareses were identified preoperatively and at FU testing (p!.005). No correlation was found between VAS for leg or back pain and DRT. Historical control subjects had a DRT of 487 (median, IQR: 116), which differed significantly at all three test times (p!.001). CONCLUSIONS: A significant reduction in DRT in patients with right- and left-sided pareses was found after surgery, indicating a positive effect of surgery. The improvement in DRT seen immediately postoperatively and the lack of a generally accepted threshold for DRT would suggest that for both patient samples, it is safe to continue driving after hospital discharge. However, patients should be informed accordingly. Ó 2013 Elsevier Inc. All rights reserved.
Keywords:
Lumbar disc surgery; Driving reaction time; Paresis; Driving safety; Lumbar disc herniation
Introduction FDA device/drug status: Not applicable. Author disclosures: MT: Nothing to disclose. RL: Nothing to disclose. BF: Nothing to disclose. CH: Nothing to disclose. PK: Nothing to disclose. KG: Nothing to disclose. AO: Nothing to disclose. MT and RL contributed equally to this work. * Corresponding author. Department of Orthopaedic Surgery, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria. Tel.: 004351250480851. E-mail address: [email protected] (M. Thaler) 1529-9430/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2013.06.052
Various studies have investigated patient outcome, cost analysis, complications, and the ability to return to work or sports after surgery for nucleus pulposus prolapse [1–6]. However, no studies on lumbar disc herniation and driving ability were found. Patients scheduled to undergo surgery commonly inquire about driving after discectomy. Driving reaction time (DRT) is one of the most important factors responsible for driving safety [7,8]. Regarding
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interventions of the spine, DRT has been investigated after lumbar fusion surgery and after selective nerve root blocks [7,9]. Although one report [7] showed an effect of left- and right-sided radiculopathy on DRT, no publications on neurologic impairment caused by disc herniation and DRT were found. The authors of these studies based their recommendations regarding return to driving on the patient’s preoperative data because official recommendations by vehicle authorities recommend a wide range of safe DRT ranging between 700 and 1,500 ms [10–12]. Therefore, the aim of the present study was to analyze the effect of right- and left-sided pareses caused by disc herniation on DRT. Additionally, we hypothesized that on longitudinal comparison, preoperative, postoperative, and follow-up (FU) DRT values would show significant changes in DRT. In addition, we compared the DRT of patients with the DRT of a historical control group.
Materials and methods Participants Forty-nine consecutive patients scheduled for standard posterior sequestrectomy or subtotal discectomy with a paresis caused by lumbar disc herniation were included in the present study. In all patients, magnetic resonance imaging confirmed disc herniation with distinct nerve root compression. The study was limited to patients with a valid driving license. Of the study patients, 23 had a neurologic deficit in the right leg and 26 in the left leg. Six patients did not complete all examinations and were excluded from the analyses. One patient had a reherniation, one patient suffered from lung cancer, and four patients did not complete the study for personal reasons. The historical control group consisted of 31 healthy subjects (19 females and 12 males; mean age, 52 years; SD, 7.7 years) with valid driver’s license. None of the healthy subjects had any spinal pathology in their medical records (Table 1). The study was approved by the local ethics committee, and all patients gave informed consent before participation.
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Table 1 Comparison of demographic data and descriptive statistics on DRT of leftand right-sided radiculopathy patients Variables Age, mean (SD) (y) Female, n Male, n Herniation level L2–L3 L3–L4 L4–L5 L5–S1 Muscle power, n 2 3 4 DRT pre-op (ms) DRT post-op (ms) DRT FU (ms) DRT pre-op !700, n (ms) O700, n (ms) DRT post-op !700, n (ms) O700, n (ms) DRT FU !700, n (ms) O700, n (ms)
Right-sided muscle weakness
Left-sided muscle weakness
Controls
47.9 (13.6) 10 10
52.1 (13.3) 8 15
52.0 (7.7) 19 12
2 2 7 9
1 3 11 8
1 14 5 761 (491) 711 (207) 645 (146)
1 12 10 651 (275) 592 (256) 569 (142)
6 14
15 7
4 14
16 6
15 5
18 4
487 (116)
DRT, driving reaction time; pre-op, preoperative; post-op, postoperative. Data are presented as median (interquartile range).
lamp lit up, indicating that the patient was not driving in a ‘‘ready to brake fashion.’’ After an interval of 5-10 seconds, the observer pushed an external trigger, invisible to the patient, which activated the red lamp and the electronic clock. The patients were instructed to apply the brake as quickly as possible with the right leg when the red light lit up. The time from the appearance of the red light to the patient operating the brake was measured in
Procedure Driving reaction time was tested with a custom-built car simulator (Fig. 1), described and validated in published literature [7,13]. An adjustable car seat was fixed on a frame with hanging pedals mounted on rubber damped pivots. As requested in a previous report [14], the position of the seat, regarding seat inclination, headrest, and seat-pedal distance, was adjustable to simulate the patient’s accustomed driving position. An external box, containing the logic gate electronics, a green lamp, and a red lamp, was positioned on a table at a constant distance in front of the car simulator. When the accelerator was fully depressed, the green
Fig. 1. Custom-made car simulator to measure driving reaction time. (Top) External box containing the logic gate electronics, clock, and green and red lamps.
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millisecond. Each patient performed three trials. Then DRT was measured 10 times at an interval of 5-10 seconds between each measurement. All patients were given the same standardized instructions. Reproducibility tests were not performed because we adhered to previously published study protocols [13]. The first test (preoperative [pre-op]) was performed 1 day before surgery, the second test (postoperative [post-op]) before discharge, and the third test (follow-up [FU]) at the FU examination 4-5 weeks after surgery. On each test occasion, the intensity of back pain and right or left leg pain was measured for all patients with a visual analogue scale (VAS), ranging from 0 for no pain to 10 for very severe pain. Leg and back pain were recorded under routine conditions and during testing. Neurologic deficit was measured on each occasion according to the Medical Research Council Scale for Assessment of Muscle Power. Driving frequency (never, once a month, once a week, and daily) and intake of analgesics were assessed on each test occasion.
under routine conditions decreased significantly (p!.001). Visual analogue scale for leg pain also revealed a significant reduction (p!.001). No significant differences were seen between VAS under routine and during testing conditions (pO.05). No correlation was found between DRT at any measurement point and driving skills. No correlation was found between VAS for back and leg pain and DRT at any of the three test times. Pain medication did not show an influence on DRT (Fig. 2). There were significant differences between left- and right-sided pareses for DRT pre-op and DRT FU (Table 2). No correlation was found between degree of weakness and DRT. No clear correlation (pO.15) was found between increase in muscle strength and decrease of DRT, although some patients with severe paresis seemed to benefit from their regained strength (Fig. 3). Both patient samples showed significantly lower DRTs throughout the whole study period compared with the historical control group (pO.05).
Statistical analysis
Discussion
Driving reaction time medians were calculated at each measurement point for each patient. To test for significant differences, the Friedman, Wilcoxon, and the MannWhitney-U tests were used as described previously [9]. In addition, we calculated the proportions of patients below or above a DRT threshold of 700 ms as several road authorities recommend maximum values between 700 and 1,400 ms. The Spearman r coefficient was used to identify correlations.
Driving reaction time before and after lumbar surgery for disc herniation has not been previously studied. Our results reveal significant improvement in DRT in the longitudinal comparison, showing a positive impact of surgery on DRT. The increase in median DRT approximately 3 days after discectomy was 50 ms for patients with right-sided paresis and 59 ms for patients with left-sided paresis. This difference would mean a difference in stopping distance of 1.39 m for right-sided paresis patients and 1.64 m for left-sided paresis patients at a speed of 100 km/h (27.78 m/s or 62.14 mph). When comparing pre-op and FU DRTs, the difference is 3.22 and 2.28 m at a speed of 100 km/h (27.78 m/s or 62.14 mph) for right- (increase, 116 ms) and left-sided (increase, 82 ms) pareses. The present results reveal that neurologic impairment of right-sided lumbar disc herniation causing paresis entailed a significantly higher DRT compared with that of leftsided paresis (Table 2). Scott et al. [14] demonstrated in healthy subjects that the fastest DRT is achieved by individuals who moved only their foot. It is also possible to brake by moving the major joints of the right leg. Our study sample consisted of patients who had mainly a neurologic impairment affecting the foot (31 of 42 patients; 73.8%),
Results Demographic data, baseline characteristics, and muscle power and DRT of the patients are shown in Table 1. The post-op examination was performed 3.5564.36 days and FU at 33.3566.04 days (mean6SD) after surgery. A statistically significant difference regarding DRT in longitudinal course was seen for both patient samples (p!.05; Table 2). Post hoc analysis at the alpha level of 0.025 revealed significant differences between DRT pre-op and DRT FU and between DRT post-op and DRT FU for patients with left- and right-sided pareses. Visual analogue scale for back pain Table 2 Comparison of DRT between pre-op, post-op, and FU testing Variables
Pre-op
Right-sided paresis
761 (491) [ [0.049] Y 651 (275)
Left-sided paresis
Post-op )
[0.028]
/
)
[0.301]
/
711 (207) [ [0.058] Y 592 (256)
FU )
[0.021]
/
)
[0.005]
/
645 (146) [ [0.034] Y 568 (142)
[0.002]
[0.003]
DRT, driving reaction time; pre-op, preoperative; post-op, postoperative; FU, follow-up. Median DRT is expressed in millisecond (interquartile range). Data in square frames: p values of longitudinal (a50.025, Mann-Whitney U test) and crosssectional (a50.05, Wilcoxon and Friedmann) comparison.
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Table 3 Level of herniation and location of motor deficit N
Site of herniation
Muscles involved
DRT, median (ms)
3 5 18
L2–L3 L3–L4 L4–L5
1.072 617 667
17
L5–S1
Quadriceps, iliopsoas Quadriceps Quadriceps, EHL, EDC, and TA EHL, EDC, TA, TS
668
DRT, driving reaction time; EHL, extensor hallucis longus; EDC, extensor digitorum communis; TA, tibialis anterior; TS, triceps surae.
Fig. 2. Box plots showing the DRT and pain medication. 0, no pain medication; 1, NSAR; 2, weak opioids; 3, strong opioids. DRT, driving reaction time; pre-op, preoperative. *, severe spike; , mild spike.
confirming the results of Scott et al. Although differences in DRT regarding the level of disc herniation and affected muscles have been found, we cannot provide recommendations for affected muscles or levels because our study sample was too small (Table 3). Further studies will be needed to give more detailed information whether the location of motor deficit has a significant impact on DRT. However, the difference to the historical control group is most likely due to several factors as increase in muscle strength alone did not show a significant correlation to DRT. Reflex inhibition causing pain and muscle weakness seems to be the most important additional factor [15]. General anesthesia should not have an impact on driving skills because the impairing effects of general anesthesia should no longer persist after 24 hours [16]. However, spinal pathologies such
as radiculopathy [7] and degenerative spinal diseases [9] may cause a delay in the neural signal transfer, and this may result in a longer DRT. Pain medication did not have a significant influence on DRT; this confirms the results of Nilsen et al., who showed that chronic pain reduces driving abilities but not opioids per se. Driving reaction times and recommendations on when patients should resume driving have been investigated in the context of several orthopedic procedures. The authors of these studies based their recommendations for a driving abstinence mainly based on preprocedure values [9]. A number of vehicle authorities recommend different values for maximum DRT, ranging from 700 to 1,500 ms [10–12]. However, no single value has been generally accepted with regard to declaring a driver safe. The German Commission on Reaction Times assumes that a DRT within 1,500 ms is safe [10]. In contrast, the Department of Transport in Britain suggests a DRT of 700 ms [11]. Driving reaction times after surgery fell within this range for all our patients. However, when discussing a safe reaction time, several factors should be considered, such cognitive level, level of fatigue, alcohol and drug anamnesis, and type and location of brake light [17–20]. Regarding the current results, we should be aware that driving safety in daily traffic may not be captured with DRT alone because external influences may also have an impact on driving safety and DRT. Our patients were tested under standard conditions. Limitations of the present study are that we did not assess the two DRT subperiods: reaction time or movement time. However, in routine traffic, these two components are of less importance when a car has to be stopped quickly. Another shortcoming is that we performed only two postoperative measurements of DRT. More frequent postoperative tests would have yielded more detailed information on the improvement in DRT.
Conclusion
Fig. 3. Box plots showing the DRT and muscle strength. Increase in muscle strength is given as the difference between preoperative and FU examination. DRT, driving reaction time; FU, follow-up. *, severe spike; , mild spike.
Patients with paresis from lumbar disc herniation showed a significantly reduced DRT compared with a healthy historical control group. Surgery showed a positive effect on DRT. In our study, the reductions in DRT were significant for patients with left- and right-sided pareses. We conclude that based on the improvement seen when
M. Thaler et al. / The Spine Journal
comparing preoperative and postoperative DRTs, it appears to be safe to continue driving after hospital discharge for patients with paresis caused by lumbar disc herniation.
References [1] Atlas SJ, Chang Y, Kammann E, et al. Long-term disability and return to work among patients who have a herniated lumbar disc: the effect of disability compensation. J Bone Joint Surg Am 2000;82:4–15. [2] Deyo RA, Weinstein JN. Low back pain. N Engl J Med 2001;344: 363–70. [3] Atlas SJ, Keller RB, Wu YA, et al. Long-term outcomes of surgical and nonsurgical management of sciatica secondary to a lumbar disc herniation: 10 year results from the maine lumbar spine study. Spine 2005;30:927–35. [4] Nellensteijn J, Ostelo R, Bartels R, et al. Transforaminal endoscopic surgery for symptomatic lumbar disc herniations: a systematic review of the literature. Eur Spine J 2010;19:181–204. [5] Smith JS, Fu KM, Polly DW Jr, et al. Complication rates of three common spine procedures and rates of thromboembolism following spine surgery based on 108,419 procedures: a report from the Scoliosis Research Society Morbidity and Mortality Committee. Spine 2010;35:2140–9. [6] Dollinger V, Obwegeser AA, Gabl M, et al. Sporting activity following discectomy for lumbar disc herniation. Orthopedics 2008;31:756. [7] Al-khayer A, Schueler A, Kruszewski G, et al. Driver reaction time before and after treatment for lumbar radiculopathy. Spine 2008;33: 1696–700. [8] Pierson JL, Earles DR, Wood K. Brake response time after total knee arthroplasty: when is it safe for patients to drive? J Arthroplasty 2003;18:840–3.
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[9] Liebensteiner MC, Birkfellner F, Thaler M, et al. Driving reaction time before and after primary fusion of the lumbar spine. Spine 2010;35:330–5. [10] Burckhardt M. Reaktionszeiten bei Notbremsvorgangen. Cologne, Germany: TUV, Rheinland; 1985. [11] Department of Transport COI. The Highway code. London, UK: Her majesty’s stationery office, 1978. [12] Royal Automobile Club of Victoria. Average reaction, breaking and stopping distances in metres at different speed with reaction time of 0.75 seconds. Melbourne, Australia: Royal Automobile Club of Victoria; 1996. [13] Ganz SB, Levin AZ, Peterson MG, Ranawat CS. Improvement in driving reaction time after total hip arthroplasty. Clin Orthop Relat Res 2003;413:192–200. [14] Scott PA, Candler PD, Li JC. Stature and seat position as factors affecting fractionated response time in motor vehicle drivers. Appl Ergon 1996;27:411–6. [15] Stokes M, Young A. The contribution of reflex inhibition to arthrogenous muscle weakness. Clin Sci (Lond) 1984;67:7–14. [16] Liebensteiner MC, Kern M, Haid C, et al. Brake response time before and after total knee arthroplasty: a prospective cohort study. BMC Musculoskelet Disord 2010;11:267. [17] Nunez VA, Giddins GE. ‘Doctor, when can I drive?’: an update on the medico-legal aspects of driving following an injury or operation. Injury 2004;35:888–90. [18] Laurell H, Lisper HO. Changes in subsidiary reaction time and heartrate during car driving, passenger travel and stationary conditions. Ergonomics 1976;19:149–56. [19] Rafaelsen OJ, Bech P, Rafaelsen L. Simulated car driving influenced by cannabis and alcohol. Pharmakopsychiatr Neuropsychopharmakol 1973;6:71–83. [20] Triggs TJ. Driver brake reaction times: unobtrusive measurement on public roads. Public Health Rev 1987;15:275–90.
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Clinical Study
Driving reaction time before and after surgery for disc herniation in patients with preoperative paresis Martin Thaler, MDa,*, Ricarda Lechner, MDa, Bernhard Foedinger, MDa, Christian Haid, PhDa, Pujan Kavakebi, MDb, Klaus Galiano, MDb, Alois Obwegeser, MDb a
Department of Orthopaedic Surgery, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria b Department of Neurosurgery, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria Received 7 June 2012; revised 28 March 2013; accepted 15 June 2013
Abstract
BACKGROUND CONTEXT: The effect of many types of surgeries on driving reaction time (DRT) has been reported. Although lumbar disc herniation is one of the most common spinal diseases, the effect on DRT has not been investigated. PURPOSE: To assess the effect of left- and right-sided pareses caused by lumbar disc herniation on DRT before and after surgery. STUDY DESIGN: Controlled prospective clinical trial. PATIENT SAMPLE: Patients undergoing disc surgery. OUTCOME MEASURES: Impact of paresis caused by lumbar disc herniation and disc surgery on DRT. METHODS: Forty-two consecutive patients (mean age, 50.3 years) were tested for DRT 1 day before surgery, postoperatively before hospital discharge, and 5 weeks after surgery. Visual analogue scale (VAS) for back and leg pain as well as pain medication and patients’ driving frequency were recorded. RESULTS: Significant improvement of DRT after surgery was seen in patients with left- and rightsided pareses (p!.005). For the right-sided paresis group, the preoperative DRT was 761 ms (median, interquartile range [IQR]: 490), 711 ms (median, IQR: 210) immediately postoperatively, and 645 ms (median, IQR: 150) at follow-up (FU). For the left-sided paresis group, DRT was 651 ms (median, IQR: 270) preoperatively, 592 ms (median, IQR: 260) postoperatively, and 569 ms (median, IQR: 140) at FU. Significant differences between right- and left-sided pareses were identified preoperatively and at FU testing (p!.005). No correlation was found between VAS for leg or back pain and DRT. Historical control subjects had a DRT of 487 (median, IQR: 116), which differed significantly at all three test times (p!.001). CONCLUSIONS: A significant reduction in DRT in patients with right- and left-sided pareses was found after surgery, indicating a positive effect of surgery. The improvement in DRT seen immediately postoperatively and the lack of a generally accepted threshold for DRT would suggest that for both patient samples, it is safe to continue driving after hospital discharge. However, patients should be informed accordingly. Ó 2013 Elsevier Inc. All rights reserved.
Keywords:
Lumbar disc surgery; Driving reaction time; Paresis; Driving safety; Lumbar disc herniation
Introduction FDA device/drug status: Not applicable. Author disclosures: MT: Nothing to disclose. RL: Nothing to disclose. BF: Nothing to disclose. CH: Nothing to disclose. PK: Nothing to disclose. KG: Nothing to disclose. AO: Nothing to disclose. MT and RL contributed equally to this work. * Corresponding author. Department of Orthopaedic Surgery, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria. Tel.: 004351250480851. E-mail address: [email protected] (M. Thaler) 1529-9430/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2013.06.052
Various studies have investigated patient outcome, cost analysis, complications, and the ability to return to work or sports after surgery for nucleus pulposus prolapse [1–6]. However, no studies on lumbar disc herniation and driving ability were found. Patients scheduled to undergo surgery commonly inquire about driving after discectomy. Driving reaction time (DRT) is one of the most important factors responsible for driving safety [7,8]. Regarding
2
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interventions of the spine, DRT has been investigated after lumbar fusion surgery and after selective nerve root blocks [7,9]. Although one report [7] showed an effect of left- and right-sided radiculopathy on DRT, no publications on neurologic impairment caused by disc herniation and DRT were found. The authors of these studies based their recommendations regarding return to driving on the patient’s preoperative data because official recommendations by vehicle authorities recommend a wide range of safe DRT ranging between 700 and 1,500 ms [10–12]. Therefore, the aim of the present study was to analyze the effect of right- and left-sided pareses caused by disc herniation on DRT. Additionally, we hypothesized that on longitudinal comparison, preoperative, postoperative, and follow-up (FU) DRT values would show significant changes in DRT. In addition, we compared the DRT of patients with the DRT of a historical control group.
Materials and methods Participants Forty-nine consecutive patients scheduled for standard posterior sequestrectomy or subtotal discectomy with a paresis caused by lumbar disc herniation were included in the present study. In all patients, magnetic resonance imaging confirmed disc herniation with distinct nerve root compression. The study was limited to patients with a valid driving license. Of the study patients, 23 had a neurologic deficit in the right leg and 26 in the left leg. Six patients did not complete all examinations and were excluded from the analyses. One patient had a reherniation, one patient suffered from lung cancer, and four patients did not complete the study for personal reasons. The historical control group consisted of 31 healthy subjects (19 females and 12 males; mean age, 52 years; SD, 7.7 years) with valid driver’s license. None of the healthy subjects had any spinal pathology in their medical records (Table 1). The study was approved by the local ethics committee, and all patients gave informed consent before participation.
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Table 1 Comparison of demographic data and descriptive statistics on DRT of leftand right-sided radiculopathy patients Variables Age, mean (SD) (y) Female, n Male, n Herniation level L2–L3 L3–L4 L4–L5 L5–S1 Muscle power, n 2 3 4 DRT pre-op (ms) DRT post-op (ms) DRT FU (ms) DRT pre-op !700, n (ms) O700, n (ms) DRT post-op !700, n (ms) O700, n (ms) DRT FU !700, n (ms) O700, n (ms)
Right-sided muscle weakness
Left-sided muscle weakness
Controls
47.9 (13.6) 10 10
52.1 (13.3) 8 15
52.0 (7.7) 19 12
2 2 7 9
1 3 11 8
1 14 5 761 (491) 711 (207) 645 (146)
1 12 10 651 (275) 592 (256) 569 (142)
6 14
15 7
4 14
16 6
15 5
18 4
487 (116)
DRT, driving reaction time; pre-op, preoperative; post-op, postoperative. Data are presented as median (interquartile range).
lamp lit up, indicating that the patient was not driving in a ‘‘ready to brake fashion.’’ After an interval of 5-10 seconds, the observer pushed an external trigger, invisible to the patient, which activated the red lamp and the electronic clock. The patients were instructed to apply the brake as quickly as possible with the right leg when the red light lit up. The time from the appearance of the red light to the patient operating the brake was measured in
Procedure Driving reaction time was tested with a custom-built car simulator (Fig. 1), described and validated in published literature [7,13]. An adjustable car seat was fixed on a frame with hanging pedals mounted on rubber damped pivots. As requested in a previous report [14], the position of the seat, regarding seat inclination, headrest, and seat-pedal distance, was adjustable to simulate the patient’s accustomed driving position. An external box, containing the logic gate electronics, a green lamp, and a red lamp, was positioned on a table at a constant distance in front of the car simulator. When the accelerator was fully depressed, the green
Fig. 1. Custom-made car simulator to measure driving reaction time. (Top) External box containing the logic gate electronics, clock, and green and red lamps.
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millisecond. Each patient performed three trials. Then DRT was measured 10 times at an interval of 5-10 seconds between each measurement. All patients were given the same standardized instructions. Reproducibility tests were not performed because we adhered to previously published study protocols [13]. The first test (preoperative [pre-op]) was performed 1 day before surgery, the second test (postoperative [post-op]) before discharge, and the third test (follow-up [FU]) at the FU examination 4-5 weeks after surgery. On each test occasion, the intensity of back pain and right or left leg pain was measured for all patients with a visual analogue scale (VAS), ranging from 0 for no pain to 10 for very severe pain. Leg and back pain were recorded under routine conditions and during testing. Neurologic deficit was measured on each occasion according to the Medical Research Council Scale for Assessment of Muscle Power. Driving frequency (never, once a month, once a week, and daily) and intake of analgesics were assessed on each test occasion.
under routine conditions decreased significantly (p!.001). Visual analogue scale for leg pain also revealed a significant reduction (p!.001). No significant differences were seen between VAS under routine and during testing conditions (pO.05). No correlation was found between DRT at any measurement point and driving skills. No correlation was found between VAS for back and leg pain and DRT at any of the three test times. Pain medication did not show an influence on DRT (Fig. 2). There were significant differences between left- and right-sided pareses for DRT pre-op and DRT FU (Table 2). No correlation was found between degree of weakness and DRT. No clear correlation (pO.15) was found between increase in muscle strength and decrease of DRT, although some patients with severe paresis seemed to benefit from their regained strength (Fig. 3). Both patient samples showed significantly lower DRTs throughout the whole study period compared with the historical control group (pO.05).
Statistical analysis
Discussion
Driving reaction time medians were calculated at each measurement point for each patient. To test for significant differences, the Friedman, Wilcoxon, and the MannWhitney-U tests were used as described previously [9]. In addition, we calculated the proportions of patients below or above a DRT threshold of 700 ms as several road authorities recommend maximum values between 700 and 1,400 ms. The Spearman r coefficient was used to identify correlations.
Driving reaction time before and after lumbar surgery for disc herniation has not been previously studied. Our results reveal significant improvement in DRT in the longitudinal comparison, showing a positive impact of surgery on DRT. The increase in median DRT approximately 3 days after discectomy was 50 ms for patients with right-sided paresis and 59 ms for patients with left-sided paresis. This difference would mean a difference in stopping distance of 1.39 m for right-sided paresis patients and 1.64 m for left-sided paresis patients at a speed of 100 km/h (27.78 m/s or 62.14 mph). When comparing pre-op and FU DRTs, the difference is 3.22 and 2.28 m at a speed of 100 km/h (27.78 m/s or 62.14 mph) for right- (increase, 116 ms) and left-sided (increase, 82 ms) pareses. The present results reveal that neurologic impairment of right-sided lumbar disc herniation causing paresis entailed a significantly higher DRT compared with that of leftsided paresis (Table 2). Scott et al. [14] demonstrated in healthy subjects that the fastest DRT is achieved by individuals who moved only their foot. It is also possible to brake by moving the major joints of the right leg. Our study sample consisted of patients who had mainly a neurologic impairment affecting the foot (31 of 42 patients; 73.8%),
Results Demographic data, baseline characteristics, and muscle power and DRT of the patients are shown in Table 1. The post-op examination was performed 3.5564.36 days and FU at 33.3566.04 days (mean6SD) after surgery. A statistically significant difference regarding DRT in longitudinal course was seen for both patient samples (p!.05; Table 2). Post hoc analysis at the alpha level of 0.025 revealed significant differences between DRT pre-op and DRT FU and between DRT post-op and DRT FU for patients with left- and right-sided pareses. Visual analogue scale for back pain Table 2 Comparison of DRT between pre-op, post-op, and FU testing Variables
Pre-op
Right-sided paresis
761 (491) [ [0.049] Y 651 (275)
Left-sided paresis
Post-op )
[0.028]
/
)
[0.301]
/
711 (207) [ [0.058] Y 592 (256)
FU )
[0.021]
/
)
[0.005]
/
645 (146) [ [0.034] Y 568 (142)
[0.002]
[0.003]
DRT, driving reaction time; pre-op, preoperative; post-op, postoperative; FU, follow-up. Median DRT is expressed in millisecond (interquartile range). Data in square frames: p values of longitudinal (a50.025, Mann-Whitney U test) and crosssectional (a50.05, Wilcoxon and Friedmann) comparison.
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Table 3 Level of herniation and location of motor deficit N
Site of herniation
Muscles involved
DRT, median (ms)
3 5 18
L2–L3 L3–L4 L4–L5
1.072 617 667
17
L5–S1
Quadriceps, iliopsoas Quadriceps Quadriceps, EHL, EDC, and TA EHL, EDC, TA, TS
668
DRT, driving reaction time; EHL, extensor hallucis longus; EDC, extensor digitorum communis; TA, tibialis anterior; TS, triceps surae.
Fig. 2. Box plots showing the DRT and pain medication. 0, no pain medication; 1, NSAR; 2, weak opioids; 3, strong opioids. DRT, driving reaction time; pre-op, preoperative. *, severe spike; , mild spike.
confirming the results of Scott et al. Although differences in DRT regarding the level of disc herniation and affected muscles have been found, we cannot provide recommendations for affected muscles or levels because our study sample was too small (Table 3). Further studies will be needed to give more detailed information whether the location of motor deficit has a significant impact on DRT. However, the difference to the historical control group is most likely due to several factors as increase in muscle strength alone did not show a significant correlation to DRT. Reflex inhibition causing pain and muscle weakness seems to be the most important additional factor [15]. General anesthesia should not have an impact on driving skills because the impairing effects of general anesthesia should no longer persist after 24 hours [16]. However, spinal pathologies such
as radiculopathy [7] and degenerative spinal diseases [9] may cause a delay in the neural signal transfer, and this may result in a longer DRT. Pain medication did not have a significant influence on DRT; this confirms the results of Nilsen et al., who showed that chronic pain reduces driving abilities but not opioids per se. Driving reaction times and recommendations on when patients should resume driving have been investigated in the context of several orthopedic procedures. The authors of these studies based their recommendations for a driving abstinence mainly based on preprocedure values [9]. A number of vehicle authorities recommend different values for maximum DRT, ranging from 700 to 1,500 ms [10–12]. However, no single value has been generally accepted with regard to declaring a driver safe. The German Commission on Reaction Times assumes that a DRT within 1,500 ms is safe [10]. In contrast, the Department of Transport in Britain suggests a DRT of 700 ms [11]. Driving reaction times after surgery fell within this range for all our patients. However, when discussing a safe reaction time, several factors should be considered, such cognitive level, level of fatigue, alcohol and drug anamnesis, and type and location of brake light [17–20]. Regarding the current results, we should be aware that driving safety in daily traffic may not be captured with DRT alone because external influences may also have an impact on driving safety and DRT. Our patients were tested under standard conditions. Limitations of the present study are that we did not assess the two DRT subperiods: reaction time or movement time. However, in routine traffic, these two components are of less importance when a car has to be stopped quickly. Another shortcoming is that we performed only two postoperative measurements of DRT. More frequent postoperative tests would have yielded more detailed information on the improvement in DRT.
Conclusion
Fig. 3. Box plots showing the DRT and muscle strength. Increase in muscle strength is given as the difference between preoperative and FU examination. DRT, driving reaction time; FU, follow-up. *, severe spike; , mild spike.
Patients with paresis from lumbar disc herniation showed a significantly reduced DRT compared with a healthy historical control group. Surgery showed a positive effect on DRT. In our study, the reductions in DRT were significant for patients with left- and right-sided pareses. We conclude that based on the improvement seen when
M. Thaler et al. / The Spine Journal
comparing preoperative and postoperative DRTs, it appears to be safe to continue driving after hospital discharge for patients with paresis caused by lumbar disc herniation.
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