Improvement In Driving Reaction Time After Total Hip Replacement

Graeme S. Carlile, Anna Cowley, Ben Thorpe, Dan Williams, Ron Spence, Michael W. Regan.

Trauma & Orthopaedic Department,
Royal Cornwall Hospital,
Truro, Cornwall, United Kingdom, TR1 3LJ.

Address for Correspondence:
Graeme S. Carlile
Trauma & Orthopaedic Department,
Royal Cornwall Hospital,
Truro, Cornwall, United Kingdom, TR1 3LJ.

Phone : 07977299952
E-mail : graeme_carlile@hotmail.com
 

Abstract:

The time at which patients should drive following total hip replacement (THR) is dependant upon recovery and the advice they are given. The Driver Vehicle and Licensing Agency (DVLA) do not publish recommendations following THR and insurance companies usually rely on medical instruction.

Brake reaction times for patients undergoing THR were measured before and four, six and eight weeks after surgery using a vehicle driving simulator. Patients were prospectively recruited. Ethical approval was granted. Participants included eleven males and nine females, mean age 69 years. Side of surgery, frequency of driving and type of car (automatic or manual) were documented. Patients with postoperative complications were excluded. No adverse events occurred during the study.

Statistical analysis using Friedman’s test demonstrated a statistically significant difference (P=0.015) in reaction times across the four time periods. Wilcoxon test demonstrated a highly significant difference between initial and six week mean results (P=0.003), and between four and six week results (P=0.001). No significant difference was found between six and eight weeks.

Our data suggests reaction times improve until week six and significantly between week four to six. Patients making an uncomplicated recovery should be considered safe to drive by week six.

J.Orthopaedics 2010;7(2)e6

Keywords:

Total hip replacement, total hip arthroplasty, hip, reaction times.

Introduction:

The point at which patients can return to driving following total hip arthroplasty (THA) is a common question. The answer is not so simple¹. In order to drive a car, the patient must be able to physically transfer into the vehicle, obtain a comfortable driving position and have full command of the operative controls. Failure to do so could be catastrophic on the road. Patient factors such as postoperative pain, mobility and the desire to avoid dislocation must all be taken in account when advising a return to driving². These multiple factors are difficult variables to measure. Arguably, the most important driving command, with reference to the lower limb, is the ability to perform an emergency stop and brake. This can be measured in the form of a driver reaction time. The driver reaction time, or emergency braking stop, is comprised of the neurological reaction time, the time taken for the driver to recognise the danger and decide to apply the brake, the transfer time as the foot is moved from accelerator to brake and the brake time as the brake is depressed from zero until the point at which the brakes are fully applied³. According to the Highway Code, the national average is 0.7 seconds⁴.

There is also a legal standpoint to consider. Many insurance companies will look to the surgeon to provide advice as to when a patient may return to driving, as naturally this is dependant on the type and extent of the surgical procedure. The surgeon may decide to refer to a national agency for guidance, such as the Driver and Vehicle Licensing Agency (DVLA) in the United Kingdom (UK). The DVLA offer guidance to doctors on over one hundred and forty different medical and surgical conditions, but not specifically following total hip arthroplasty. The most recent guide published in February 2009⁵ states that licence holders wishing to drive after surgery (generic, without specific reference to THA), should establish with their doctor when it is safe to do so and should check their insurance policy. In the absence of firm guidance from the DVLA, the surgeon could review the literature for the answer, though predictably this is also a little grey. Few studies have tackled this question and those that have, reported different conclusions. In a study from the Oxford Orthopaedic Engineering Centre, Macdonald and Owen⁶ concluded from their study of twenty-five patients, that most were safe to return to driving from week eight. In a sponsored American study of ninety patients, Ganz and Levin⁷ concluded that patients manage to achieve their preoperative reaction time at weeks four to six, and improve thereafter.

At our own institution, we allow patients making a satisfactory recovery to return to driving at six weeks. This is based loosely around choosing the mid-point of the studies above and as our follow-up clinics occur at week six. We recognised this practise needed to be evidenced based, and performed our own study based around driving reaction times following THA. Our aims were to evaluate if our current practise was safe, and in a similar fashion to previous studies, determine at which point there is a significant improvement in postoperative reaction times.

Materials and Methods:

We were fortunate to be granted access to a driving simulator (Media in Progress, Srl, 00165, Roma, Italy) at a regional mobility centre. The driving simulator is used on a daily basis in the assessment of fitness to drive. A single driving consultant whom is familiar with the equipment and processes involved, was recruited to perform our testing.  Subjects were asked to accelerate to a constant speed of thirty miles per hour (mph) and perform an emergency braking stop when signalled to do so by a random red light, located on top of the apparatus (figure 1).

Figure 1. Driving vehicle simulator

In order for their attempt to be registered a successful, subjects had to achieve a minimum brake pressure of one hundred and fifty Newton metres (Nm). Subjects were permitted two unrecorded practise attempts to familiarise themselves with the process, followed by three recorded attempts. Unsuccessful attempts were recorded as such. The total reaction time, including neurological time, transfer time and the time taken between applying the brake and achieving 150 Nm, the brake time was recorded as one measurement in seconds (figure 2). Patients were assessed pre-operatively and at four, six and eight weeks post-operatively.

Figure 2. Driving reaction time

Patients were recruited on a voluntary basis prospectively. All patients undergoing primary total hip arthroplasty using a stemmed prosthesis were eligible. Patients undergoing total hip resurfacing or a revision procedure were not eligible. Patients were recruited at random, from either of our institutions two pre- assessment clinics. Upon receiving a hospital letter stating the date of pre-assessment, an information leaflet regarding the research was also included. After formal pre-assessment had finished, patients were asked if they wished to volunteer for the study by a pre-assessment nurse, who had been fully briefed regarding the study eligibility criteria and design requirements. Patients requiring further information were given the telephone number of an investigating doctor to contact. All patients entering the study were fully consented regarding the potential risks and free to withdraw at any point. Recruited patients were provided with appointments for pre and post-operative assessment at the mobility centre. No incentives were offered for recruitment and patients received their surgery according to their place on the waiting list. The operative surgeon was not informed of individual patient recruitment into the study in an attempt to avoid bias. Exclusion criteria mid-study included any patient that experienced a serious post-operative complication, as participation may compromise recovery and jeopardise the validity of the results. Ethical approval for the study was obtained.

Results :

In total 20 patients were recruited comprising of 9 females and 11 males with a mean age of 69 years (range 53-78). The primary diagnosis in all cases was osteoarthritis. Of the patients, 5 had a left sided procedure and the remaining 15 a right-sided procedure. With regards to driving practises, 12 patients drove an automatic vehicle and the remainder a manual. The majority of patients, 14, drove more than six times per week, 5 two to four times per week and 1 patient only drove once to twice per week. No complications were experienced during testing. Of the 20 patients, 15 completed the full remit of testing preoperatively and at four, six and eight weeks. Five patients completed testing preoperatively, at four weeks and six weeks, but did not attend for final testing at eight weeks. All patients tested managed to record three successful reaction times at their respective time periods. Not once did any patient record an unsuccessful attempt.

The statistical analysis was overseen by our institutions onsite statistician using SPSS software (version 16, SPSS Inc, Chicago, Illinois, USA). The three-recorded reaction times from each patient for each time period, were tabulated in order to calculate the overall mean reaction time (table I).

Table I: Mean reaction times for each time period.

Given that our data set was small and therefore not normally distributed, non-parametric testing was used. Friedman’s test demonstrated a significant difference of 0.015 across all four-time periods, but did not reveal at which interval. Wilcoxon signed rank tests were used to analyse the intervals and found a highly significant difference between the pre-operative and 6 week time period (P=0.003) and between weeks 4 and 6 (table 2).

Table 2. Analysis of reaction times across time periods

Figure 3. Reaction times according to sex

Figure 4. Reaction times for left and right hip replacements

Discussion :

With reference to our study aims, we feel our results demonstrate that reaction times do improve with time, and significantly improve by week six. We were particularly encouraged to find such a highly significant improvement between the preoperative and six weeks time period and across the four to six week interval. Review of individual mean scores for each patient at week seix revealed no score above the 0.7 second average reaction time in the Highway Code, suggesting that all patients in our study would have had satisfactory reaction times to return to driving at that stage. This does however raise the question of why we did not find statistically significant results at eight weeks, though the mean score was 0.61 seconds. We believe this is due to the smaller sample size of only fifteen patients that completed testing at week eight. Analysis of individual patient scores reveals an anomaly, “Patient 14”, whom despite obtaining a six-week score of 0.65, then went onto register an eight week score of 0.73 seconds (figure 5). This score in itself was a mean of all three attempts, two of which had been particularly encouraging at 0.57 and 0.64 seconds, but was completely skewed by an extremely slow final attempt of 0.99 seconds.

Figure 5. Mean reaction times and “Patient 14”

The small sample size of only twenty patients is a without question a limitation to this study. Our local region is mainly rural, serving a population of 531,600 people⁸ across 1,376 square miles⁹. In order to attend for testing, patients living away from the hospital in remote areas needed to travel a considerable distance at their own cost, which was a major barrier. As the study was not funded, we could not offer to pay for travel expenses. The small sample size has had an impact not only on our eight-week results, but also the comparison between right and left hips. One would expect those patients undergoing a right-sided procedure to have a longer reaction time, as most people brake using the right foot. With only five left sided procedures in our cohort, we did indeed notice this trend, but the data was not statistically significant. However, given that the majority of our data is based on right-sided results, it could be argued that it is representative of a worst-case scenario.

From the literature there are few comparable studies. In the paper by MacDonald and Owen⁶, twenty-two patients were assessed, nine left THA’s, twelve rights and one bilateral procedure, in addition to fifteen normal subjects. Conceptually the study was similar in the use of a driving simulator, but with a younger cohort of patients (mean age 58 years) and lower braking force threshold of 100 Nm (compared to 150 Nm). They too found a statistically significant improvement with time across all periods, but did not examine the time intervals. Their recommendation of week eight was based heavily around the 0.7 second average reaction time in the Highway Code. In the paper by Sandy Ganz et al⁷, a sponsored American study comprising ninety patients, fifty-five of which were tested at one year. Patients were tested pre-operatively, at 1 week, 4-6 weeks, 26 weeks and at 52 weeks. A statistically significant result was found between the pre-operative mean, and each time interval. At six weeks the mean driving reaction time was found to be 0.06 seconds faster than the pre-op score, comparable to the 0.056 second improvement in our study. Interestingly, Ganz found a significant improvement between week six and one year as one may expect, but not between twenty-six weeks and one year, suggesting reaction times are better than pre-op by week six and continue to improve up until a defined point in postoperative recovery and return to normal function.

Conclusions:

Brake reaction times following primary uncomplicated total hip arthroplasty improve with time. Our data would suggest this occurs by week six. Therefore with such patient’s in mind, it would be reasonable to permit driving from six weeks onwards. This is supported by one other major study. We recommend surgeons should fully assess that the patient is making a satisfactory recovery and document their advice. Patients in the UK should be made aware of the DVLA’s guidance (5) on driving following surgery; “that it is the responsibility of the driver to ensure that he/she is in control of the vehicle” and check with their insurance provider first.

Reference :

1. Cooper JM. Clinical decision making: doctor, when can I drive? Am J Orthop. 2007 Feb;36(2):78-80.

2. Peak EL, Parvizi J, Ciminiello M, Purtill JJ, Sharkey PF, Hozack WJ, Rothman RH. The role of patient restrictions in reducing the prevalence of early dislocation following total hip arthroplasty. A randomized, prospective study. J Bone Joint Surg Am. 2005 Feb;87(2):247-53.

3. Spalding TJ, Kiss J, Kyberd P, Turner-Smith A, Simpson AH. Driver reaction times after total knee replacement. J Bone Joint Surg Br, Sep 1994; 76-B: 754 - 756.

4. Department of Transport. The Highway Code. London: HMSO, 1978.

5. Department of Transport. At a glance Guide to the current Medical Standards of Fitness to Drive. Driver Medical Group, DVLA, Swansea, February 2009.

6. MacDonald W, Owen JW. The effect of total hip replacement on driving reactions. J Bone Joint Surg Br. 1988 Mar;70(2):202-5.

7. Ganz SB, Levin AZ, Peterson MG, Ranawat CS. Improvement in driving reaction time after total hip arthroplasty. Clin Orthop Relat Res. 2003 Aug;(413):192-200.

8. UK England & Wales Scotland and Northern Ireland 2007. Office for National Statistics, http://www.ons.gov.uk . Accssed 28^th August 2009.

9. UK Standard Area Measurements 2007. Office for National Statistics, http://www.ons.gov.uk . Accssed 28^th August 2009.

This is a peer reviewed paper 

Please cite as: Graeme S. CarlileM: Improvement In Driving Reaction Time After Total Hip Replacement

J.Orthopaedics 2010;7(2)e6

URL: http://www.jortho.org/2010/7/2/e6

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