Since the advent of anatomic total shoulder replacement1 and the subsequent evolution in prosthetic designs2, shoulder arthroplasty has been shown to provide patients with marked improvements in shoulder function, pain relief, and quality of life2-7. Following shoulder arthroplasty, patients frequently inquire as to when they can safely resume driving a motor vehicle. Compromise of any of the cognitive, neurologic, and musculoskeletal systems involved in operating a vehicle can substantially hinder one’s ability to safely drive. Numerous studies have investigated the impact of a variety of orthopaedic interventions on driving performance8-27. While studies have shown that up to 65% of patients report the ability to resume driving following shoulder arthroplasty6,7, to our knowledge, there have been no studies elucidating an appropriate time frame in which to resume driving. As a result, no evidence-based recommendations exist to determine a patient’s “fitness to drive” in the perioperative or postoperative period28,29. With the use of a validated driving simulator model, we sought to better delineate the time interval at which a patient’s driving performance returns to baseline following anatomic or reverse total shoulder arthroplasty.
Materials and Methods
The institutional review board of New York University approved this study.
We utilized a driving simulator to reproduce “typical” driving conditions in an automatic-transmission vehicle. To assess the change in driving performance, we employed a previously established testing model, including both hardware and software setup18,30,31. The hardware and software simulation setup was previously validated in numerous studies32-36. Windows STISIM Drive software (version 2.0; Systems Technology) was used to design customized circuits to acclimatize study participants to the software as well as to test them in simulated real-world driving conditions. The driving simulator and program software are shown in Figure 1.
Simulated Driving Environment
Each participant was allowed a single training-circuit session prior to the initial trial, during which they drove freely on a simulation circuit in order to gauge how responsive the simulator was to their movements as well as to test their brake reaction time. During the training-circuit session, the participants utilized both hands while driving, with no sling immobilization. A brake reaction time was calculated using the average of 3 reaction times (full depression of the brake) in response to sudden stop signals on the display. This reaction time was used to calibrate the simulation course before each driving trial for each study participant to control for variability between trials in eye-to-foot response time. Once the course was calibrated, a simulated driving session, lasting approximately 8 minutes, was conducted. The simulated driving circuit was designed to represent a suburban environment, recreating standard turns, traffic intersections, pedestrian crosswalks, and several hazards routinely encountered during driving situations.
Custom-Designed Driving Circuit
Patient-specific customization of the simulated circuit allowed for the elimination of confounding variables in order to directly investigate the impact of shoulder function on driving performance. Using a patient-specific response time, the simulated speeds when approaching the hazards were computer-controlled to allow for uniform analysis.
Patients who were between 20 and 80 years of age and were indicated for anatomic total shoulder arthroplasty or reverse total shoulder arthroplasty and who had a valid driver’s license were eligible for inclusion. Exclusion criteria included any history of a debilitating systemic disease or any compromising neurologic condition. Thirty-seven patients who were scheduled to undergo anatomic or reverse total shoulder arthroplasty were identified and enrolled. We recorded each patient’s comorbidities, number of years of driving experience, dominant arm, total number of previous automobile accidents, annual number of miles driven, and number of hours slept the previous night. Following informed consent, each patient underwent 4 driving simulation trials. The first was conducted preoperatively. Three subsequent trials were conducted at postoperative week 2 (PO2), week 6 (PO6), and week 12 (PO12). The patients did not wear a sling while using the driving simulator.
A custom MATLAB (MathWorks) program converted real-time driving data into quantifiable measures of “driving performance.” Driving performance was evaluated by examining the overall number of collisions, the number of centerline crossings, and the number of “off-road excursions.” The total number of collisions encompassed both off-road collisions, which occurred when patients veered too far laterally from the boundaries of the computerized driving circuit and experienced an off-road crash, and on-road collisions, which occurred if a patient’s vehicle collided with other cars, pedestrians, work cones, or cyclists designed to be in the program. The number of centerline crossings was measured by the number of times the patient’s vehicle traversed the centerline, crossing into oncoming traffic. Lastly, the number of off-road excursions was determined by the number of times the patient’s vehicle traversed the lateral road edge and traveled onto the grass, although did not crash off-road.
In addition, scores on the Shoulder Pain and Disability Index (SPADI) and on a visual analog scale (VAS) for pain were gathered prior to each driving session, serving as measures of clinical functional outcomes (with 0 indicating the best score, and 100, the worst).
Descriptive analyses of patient characteristics and outcome measures summary were obtained via the calculation of the mean and standard deviation (SD) for continuous and categorical variables. Additionally, results from a previous study by the senior author (J.Z.) employing the same methodology were used for a qualitative comparison of driving performance among healthy volunteers31.
All of the outcome data were checked for normality with the Shapiro-Wilk test, and the homogeneity of variance was checked prior to analyses with the F test. A repeated-measures ANOVA (analysis of variance) was used to assess changes in driving performance outcomes over the 4 time points. Post-hoc pairwise comparisons of groups were performed with t tests to identify differences. Bonferroni adjustments were applied to the respective confidence intervals. A linear mixed-effect model was used to test for the association between various covariates and patients’ driving performance outcomes. Driving performance outcomes were treated as dependent variables, and demographic information and functional scores were treated as covariates. The analysis was first performed in a univariate manner, using a linear mixed model to identify possible predictors of patients’ driving performance. A multivariate linear mixed-model analysis was then performed, including variables that were significant in the univariate analysis as well as potential confounders, such as years of driving and miles driven per year. All statistical analyses were conducted using the R statistical package (http://www.r-project.org).
Of the 37 patients enrolled in this study, 30 successfully completed all 4 phases of the simulation testing. Five patients elected not to undergo surgery, and 2 did not complete all of the driving trials. Twenty of the 30 patients (6 male and 14 female patients) underwent anatomic total shoulder arthroplasty using the Equinoxe Primary total shoulder system (Exactech). The remaining 10 patients (5 male and 5 female patients) underwent reverse total shoulder arthroplasty using the Equinoxe Reverse total shoulder system (Exactech). Patient medical comorbidities included hypertension, diabetes, hypothyroidism, inflammatory arthritis, chronic obstructive pulmonary disease (COPD), asthma, coronary artery disease, atrial fibrillation, and cancer (breast, prostate, and lymphoma); 16 patients were classified as American Society of Anesthesiologists (ASA) II, and 14 were classified as ASA III.
The average time to the completion of testing for PO2, PO6, and PO12 was 2.3 weeks, 6.4 weeks, and 12.9 weeks, respectively. All surgeries were performed at a major North American center by 2 fellowship-trained shoulder arthroplasty surgeons with 10 and 25 years of experience, respectively; each surgeon performs >100 arthroplasties annually. A standard deltopectoral approach was used, and each patient underwent subscapularis tenotomy and repair. The average surgical time for all procedures (and standard deviation) was 91.6 ± 20.9 minutes. There were no intraoperative or immediate postoperative complications, including fracture or infection, in our patient cohort. Of the 30 patients included in this study, only 1 patient required revision from anatomic to reverse shoulder replacement at 1 year postoperatively, for a greater tuberosity fracture.
A descriptive summary of data is presented in Table I. A repeated-measures ANOVA revealed that the total number of collisions and centerline crossings differed significantly across the time points, as shown in Table II. The overall mean number of collisions increased from 5.90 ± 4.25 preoperatively to 7.43 ± 4.75 at PO2, and subsequently decreased to 5.60 ± 3.82 and 4.00 ± 3.16 by PO6 and PO12, respectively. The same pattern appeared for the overall mean number of centerline crossings, which increased from 21.43 ± 7.69 preoperatively to 22.10 ± 7.70 at PO2 and subsequently decreased to 20.90 ± 8.86 and 16.30 ± 5.11 by PO6 and PO12, respectively. Post-hoc analysis with a Bonferroni correction indicated that the number of collisions and centerline crossings at PO12 was significantly lower than at PO2 (p = 0.0079 and p = 0.019, respectively) (Fig. 2).
In the univariate linear mixed-model analysis, VAS and SPADI scores for pain were positively associated with the number of collisions over time. Male patients had significantly fewer collisions and off-road excursions than did female patients, as shown in Table III. Older age was also positively associated with the total number of collisions and off-road excursions. In the multivariate mixed-effects model, age and sex remained significant predictors of the number of off-road excursions.
In recent decades, there has been a considerable increase in the number of shoulder arthroplasties performed annually, with the number rising from 10,000 per year in 2002 to >36,000 per year in 201028,37,38. One survey-based study looking at the preoperative expectations of patients undergoing total shoulder arthroplasty showed that up to 73% of patients viewed the improved ability to drive postoperatively as important39. Similar survey-based studies looking at patient-reported activities after shoulder arthroplasty reported that up to 65% of patients reported the ability to resume driving6,7. Consequently, it is commonplace for patients to ask clinicians for recommendations about when they can safely resume driving following shoulder arthroplasty.
In the present study, using a validated driving simulator model32-36, we sought to better delineate the time interval at which patients can safely return to driving following shoulder arthroplasty. Our data showed that driving performance returned to baseline at 6 weeks following shoulder arthroplasty and actually improved compared with baseline at 12 weeks postoperatively.
We chose 2 weeks as the minimum duration before testing because, depending on surgeon preference, most rehabilitation protocols endorse immobilization with use of a sling for the first 2 to 6 weeks during the initial protective rehabilitation phase postoperatively40-45. In the United States, the National Highway Traffic Safety Administration recommends not driving with any splint or immobilization device29. Additionally, previous studies have shown that driving with sling immobilization leads to the inability to effectively perform evasive maneuvers in hazardous driving scenarios8,31. Hence, our testing cohort was evaluated preoperatively and at 3 standard follow-up times to account for the typical time points a patient would no longer be immobilized, and hence, more likely to drive.
The evaluation of the total number of collisions was reflective of hazardous driving scenarios, whereby the driver faces road hazards and more difficult turns. In hazardous driving scenarios, the repeated-measures ANOVA demonstrated a significant difference in the number of total collisions across the testing intervals. At PO2, patients were found to be involved in the greatest number of collisions. The total number of collisions decreased to preoperative levels at PO6. The 12-week time point demonstrated a significant decrease in the total number of collisions; driving performance with respect to hazardous scenarios was most improved at PO12. In a previous study that utilized the same driving simulator hardware and software setup, we found that healthy volunteers sustained approximately 2.2 ± 1.5 collisions31. The current patient cohort sustained 5.9 ± 4.3 collisions at the preoperative testing interval and 7.4 ± 4.8 at PO2; the number of collisions decreased to 5.6 ± 3.8 and 4.0 ± 3.2 by PO6 and PO12, respectively. The reason for the higher total number of preoperative collisions in our patient cohort when compared with healthy volunteers is unclear. However, we speculate that this may be related to individual variability in the ease of using the driving simulator with respect to baseline shoulder pathology, age, and medical comorbidities. Nonetheless, our data demonstrated improved driving performance with respect to our specific patient cohort.
The number of centerline crossings and the number of off-road excursions were recorded at all time points and, hence, were more reflective of day-to-day driving performance. There was a significant decrease in the total number of centerline crossings at the PO12 interval when compared with all testing intervals, including preoperatively. Hence, in the context of everyday driving, driving performance was optimal at PO12, with better vehicle control, when compared with the preoperative performance. Moreover, data from a previous study showed that patients who underwent shoulder arthroplasty had vehicle control similar to that of young healthy volunteers, with 16.9 ± 4.2 centerline crossings sustained by the healthy volunteers31 compared with 16.3 ± 5.1 centerline crossings sustained by the current patient cohort at the PO12 testing interval. Given that the patient cohort sustained 21.4 ± 7.7 centerline crossings at initial preoperative testing, we can infer that shoulder arthroplasty may actually improve driving ability in patients with notable glenohumeral arthritis.
As expected, there were improvements in the VAS pain and SPADI scores as patients progressed from preoperative status to PO12. Univariate analysis showed that pain (VAS and SPADI-pain) had a significant effect on the number of collisions, and both univariate and multivariate analysis found that the VAS score had a significant effect on the number of collisions. It is interesting to note that, postoperatively, patients were found to have the highest pain scores at PO2, which correlated with a higher number of recorded collisions and off-road excursions. This testing period was reflective of the early postoperative period, when patients were kept immobilized with use of a sling; the resultant poor driving performance is likely secondary to a combination of pain and stiffness from postoperative activity restrictions. Consequently, improvements in pain and function postoperatively were correlated with improved driving performance in the context of number of collisions and off-road excursions. These findings are critically important, as clinicians can use patient pain metrics to guide their recommendations regarding driving ability.
Pain and disability may not be the only limiting factors with regard to shoulder function. It has been postulated that proprioception plays an important role in normal shoulder function46 and subsequent postoperative outcome and rehabilitation. Cuomo et al. reported that patients with advanced glenohumeral arthritis had a significant decrease in proprioceptive function, which markedly improved after total shoulder arthroplasty47. Given the upper-extremity maneuvering required when operating a vehicle in varying driving scenarios, this may partially explain why patients may exhibit improved driving performance by 12 weeks postoperatively compared with preoperative performance. Studies have shown that patients generally begin to resume a more active lifestyle during this time period48,49. One case series showed a mean time to partial return to sports activities at 3.6 months, with full participation at 5.8 months48. Furthermore, the 12-week postoperative time point represents an interval at which surgeons begin to advance patient activity, with approximately 50% of surgeons allowing their patients to begin athletic participation at that time point49.
Analyses of the data showed that sex and age play a role in driving performance after shoulder arthroplasty. Univariate analysis showed that sex had a significant impact on driving performance, with female sex demonstrating a negative effect on driving performance. This is contrary to the findings of cross-sectional studies of driving incidents, which showed that male sex was more predictive of traffic accidents given higher risk-taking potential50,51. However, multivariate analysis in the present study showed that sex was no longer significant when driving history was also factored into the analysis. It is likely that sex-based differences are less important than driving history (number of years), which was found to have a significant effect on driving performance in multivariate analysis. Age was also found to have a significant impact on driving performance in both univariate and multivariate analyses. It is well established that increasing age has a negative impact on driving ability52,53 given the decline in sensory, cognitive, and physiologic functions with increasing age, which likely contribute to poor driving performance among the elderly.
While our study has important implications for driving recommendations following shoulder arthroplasty, there were several limitations. A driving simulator cannot truly replicate an actual vehicle and the day-to-day driving environment, including the comfort and habit of driving a particular vehicle and utilizing a familiar driving route. Furthermore, some of the improvement seen in successive driving trials may represent a cognitive learning-curve phenomenon, which may have had a confounding effect on any improvements seen in successive driving trials. Additionally, while the circuits created for this study were representative of real-world circumstances, there are aspects of driving that we were not able to test, such as reversing, parallel parking, and performing a 3-point turn. Furthermore, aside from functional limitations of the shoulder, other aspects of perioperative care may have contributed to worse driving. The sedative effects of narcotic analgesics have been well documented, as their use and/or abuse has been correlated with inferior driving ability54-57. However, no patient in the current study reported use of such drugs prior to testing. A major limitation of our study was that a large percentage of our patient population lived in a major metropolitan area in which the annual number of miles driven per capita is approximately 2,50058. The annual number of miles driven per capita in the United States is approximately 13,00059, which is substantially higher than that of our study cohort. Hence, our results may not be reflective of the general population.
Evidence-based guidelines for the return to driving after shoulder arthroplasty have become imperative in light of the rapidly increasing rate of these procedures. Our data demonstrated decreased driving performance in the early postoperative period following shoulder arthroplasty and a return to preoperative levels by 6 weeks postoperatively. Furthermore, patients had significant improvements in driving performance in both hazardous situations and everyday driving at the 12-week postoperative period. Our results also showed that high patient-reported pain scores, older age, and less driving experience had a negative impact on driving performance in the postoperative period. On the basis of our findings, clinicians can suggest a window of 6 to 12 weeks postoperatively for the gradual return to driving. However, for patients of older age, with less driving experience, or with a greater pain level, a return to driving at closer to 12 weeks postoperatively should be recommended.
Investigation performed at the Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, NY
Disclosure: No external funding was received for this study. The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article.
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