The most important finding of the study was that only BPF showed a significant decrease after TKR and preoperative baseline levels were only reached 6 weeks after surgery. In addition, subjective outcome parameters did not show satisfying results until 6 weeks after surgery. These results suggest that a timeframe of 6 weeks after TKR should be kept before patients can safely start driving again confirming our hypothesis.
A majority of patients view rapid restoration of the postoperative driving ability as a key issue due to its necessity for mobility and independence. The ability to perform a quick and effective emergency stop is essential for the safe operation of a motor vehicle. The heterogeneity of the published data illustrates the difficulties encountered when trying to define an appropriate recommendation with due consideration of individual circumstances. This study, therefore, aimed to assess driving ability as defined by NRT, BRT, and BPF as well as subjective outcome parameters. Measurements were taken at different time points over the perioperative period to evaluate different stages in the restoration of a patients driving ability following TKR.
NRT, BRT, and BPF exhibited a large inter-individual range in the control group. BRT in younger (32 years) control subjects (706 ms) was similar to values previously reported (700–750 ms) . In contrast, the older patient group (66 years) exhibited significantly slower (985 ms) preoperative reaction times.
Of note, we found braking response times to be faster for the male control population. As NRT measurements were similar, the cause seemed to be a shorter transfer time from the accelerator to the brake pedal. Similarly, Green and Li et al. found women to have a slower brake reaction time (BRT) in critical situations [6, 10]. In contrast to our results, Li and colleagues found that women responding to an emergency signal while operating a mobile phone responded slower than men, but ended up with a shorter braking distance due to more efficient braking . Other studies, however, failed to show any significant gender differences regarding BRT [1, 5]. In summary, the available evidence does not provide clear evidence for gender-specific recommendations regarding driving safety.
We also found a correlation between age and reaction time, although the comparison is limited as the majority of older patients complained of severe knee pain. Besides pain, restriction of movement due to advanced gonarthrosis may be a decisive factor for the found age-dependent differences. Other authors have confirmed this observation [2, 4]. In contrast, Dalury et al. described a significantly shorter preoperative BRT of 530 ms in patients with gonarthrosis; while, Hernandez et al. observed a value of 692 ms [1, 7]. On a critical note, comparison of reaction times is complicated by great variances (430 ms–1330 ms) due to the heterogeneity of patient groups and the simulators employed [1, 7, 8, 11, 12]. Thus, driving ability recommendations based on NRT or BRT only might be prone to error and insufficient in many cases. As discussed by McLeod et al., evaluating BPF is critical to make reliable recommendations . In contrast to the reaction time results, this study did not determine any significant differences in BPF between genders or between the healthy control group and the preoperative patient cohort. Hence, preoperative chronic knee pain (NRS 5.1) does not seem to be associated with any significant reduction in BPF. No study so far has described influential factors or a correlation between BPF and age. In conclusion, BPF measurements offer decisive advantage for the evaluation of driving ability, especially after surgical intervention.
Both reaction time measurements and BPF reported in literature show pronounced inter-individual fluctuations, complicating establishment of universally applicable quantitative thresholds. With regard to assessing driving abilities, priority should be given to considering the individual preoperative baseline parameters and not to obtain arbitrarily defined thresholds.
Overall, NRT increased by 55 ms and BRT by 105 ms immediately after surgery. Despite the absence of statistical significance, the latter is equivalent to an extension of the braking distance by approximately 1.5 m at a speed of 50 km/h and to an increase of approximately 3 m at a speed of 100 km/h. Jordan at al. observed a similar non-significant prolongation of the BRT by 150 ms at 8 days after lower limb surgery . Other authors also found no significant prolongation of BRT during the postoperative period . On the other hand, a recent meta-analysis by Van der Velden et al. identified nine prospective studies providing partly inhomogeneous recommendations based solely on changes in reaction time . Pooling all data after right-sided TKR, reaction time reached preoperative baseline levels 4 weeks after TKR. However, none of these studies evaluated braking force as an additional outcome parameter. Another systematic review by Di Silvestro et al. concluded that operation of a motor vehicle is possible 4 weeks after TKR based on changes in reaction time . However, only 4 of the 25 investigated reports considered braking force for their recommendations (10 days to 12 weeks), and none of them focused on TKR patients . To our best knowledge, only Spalding et al. evaluated BPF as an additional safety parameter after TKR . However, this study is 26-years old and is therefore not taking current technical developments such as fast track concepts and modern rehabilitation protocols into account.
BPF was found to be significantly decreased immediately after surgery. Although no statistically significant difference was detected in the 3rd–4th postoperative weeks compared to the preoperative levels, baseline values were only fully restored after the 6th postoperative week. Furthermore, no significant difference between control and patient group was observed in week 3/4 after surgery. At present, there is paucity of literature concerning braking force after total joint replacement . Jordan et al. investigated BPF over time (preoperatively, 8 days, 6, 12, and 52 weeks postoperatively) after hip replacement : for these patients, BPF was significantly reduced and did not return to preoperative levels until week 12. In contrast, the BRT had already been restored in the 6th postoperative week. The prolonged convalescence in the Jordon et al. study when compared to the results presented in our study may be due to postoperative rehabilitation differences between knee and hip replacements, as well as mobility restrictions relating specifically to the hip.
In addition to the objective evaluation of driving ability by measuring NRT, BRT and BPF, subjective parameters like pain levels or subjective fitness to drive are key parameters in the decision-making process. Regardless of the statistical significance of the physical parameters assessed in this study, patients did not rate their own driving ability to be “good” until the 6th postoperative week. Moreover, crutches were used postoperatively for approximately 5–6 weeks. Current german case-law interprets the use of walking aids as negligent behaviour and could therefore attribute to (partial) liability in the event of a traffic accident, regardless of an individual’s subjective physical fitness (§ 315c of the German Criminal Code, StGB). Taking into account all subjective and objective parameters, patients’ driving ability was restored to preoperative levels 6 weeks after surgery. These results suggest that active participation in road traffic should generally not take place before the 6th postoperative week.
Some limitations apply to this study. The control group was not matched for age or gender. It was, therefore, not possible to reliably evaluate the impact of age and pain on NRT, BRT, and BPF. Nonetheless, comparison with preoperative baseline values appears sufficient due to the described inter-individual fluctuations. Furthermore, comparing patients to a healthy younger control group results in an even stricter evaluation. The authors are also aware that a time range of approximately 14 days for the 3rd and 4th measurements might impact the braking behaviour. Due to patient-initiated changes of scheduled appointments and organisational reasons, it was not possible to assess all patients at the exact same day after surgery. However, as rehabilitation and function improve only slowly over the postoperative course, the authors are confident that this does not result in a substantial bias of the data. Furthermore, correlation analysis failed to show any influence of time ranges within the separate measurement timepoint. A third limitation is that the effects of brake boosters on emergency braking were not considered. This study was not able to evaluate the extent to which a modern brake booster might achieve adequate braking, even with reduced BPF. By definition, however, emergency braking requires a rapid and powerful braking manoeuvre.