Session V - Foot and Ankle

Lower Extremity Driving Performance after Ankle Fracture

Kenneth A. Egol, MD; Ali Sheikhzadeh, PhD; Sam Moghtaderi, BS; A. Barnett; Nirmal C. Tejwani, MD; Kenneth J. Koval, MD; New York University-Hospital for Joint Diseases, New York, New York, USA

Purpose: Driving an automobile requires a certain amount of lower extremity strength and coordination as well as the ability to rapidly respond to emergency situations by switching the foot between the brake and acceleration pedals of the car. Currently no guidelines exist for the clinician or patient to ascertain the minimal functional ability to drive a car after trauma to the ankle or immobilization. In particular, there is a lack of a structured protocol for use with patients who have had lower extremity injuries for the assessment and evaluation of functional abilities for the safe operation of an automobile.

Purpose: The purpose of this IRB-approved study was twofold. The first was to better understand the function of the lower extremity during different tasks that simulated driving an automobile as performed by healthy volunteers. We also wished to determine when patients recover the ability to operate the foot controls of an automobile after surgical repair of an ankle fracture.

Methods: A computerized driving simulator was developed and tested. The Labview software (National Instruments, Austin, Texas) was used to collect and display data via an analog/digital board (AT-MIO-64, National Instruments) with a sampling rate of 1000 Hz from accelerator and brake pedals. Three groups of subjects were tested. First, healthy volunteers (N = 11) were tested once to establish normal mean values for variables tested. A second group of patients who underwent repair of a right (driving) ankle fracture (N = 31) were tested at 6, 9, and 12 weeks after surgery. Patients were tested with a series of driving scenarios (city, suburban, and highway) with reaction and response times to various stimuli recorded. SMFAs and ankle/hindfoot scores were recorded at 6 and 12 weeks and compared with results of the driving test. Descriptive statistics (mean ± SD) of the subject's demographic data and results of clinical and functional outcome measures were reported. In addition, repeated analysis of variance was used to investigate the effect on total brake time and brake travel time. A P value £ 0.05 was considered significant.

Results: Total brake time (TBT) was 1009.58 msec for group I, and 1273.68 msec, 1127.18 msec, and 1066.79 msec for group II at 6, 9, and 12 weeks after surgery. (P = 0.0017); TBT consistently improved for each of the driving scenarios at each successive data point (P = 0.05). At 6 weeks this increased total braking time translated into an increased breaking distance of twenty-two feet at 60 mph. At 9 weeks it translated into 4.1 feet at 60 mph. The functional outcome improved at each successive visit, although no statistical significance was found.

Discussion: Some laws hold the physician who clears an impaired patient to drive responsible for the patient's actions. Little is known, however, of the minimum level of function needed to safely operate a motor vehicle. The authors of previous studies have reported driving performance of patients after common orthopaedic procedures. On the basis of our data, it appears that driving performance with regard to lower extremity braking function was impaired at 6 weeks after surgery. Normal braking function appeared to return by 9 weeks after surgical repair of a right-sided ankle fracture. No significant further improvement was seen between 9 and 12 weeks with regard to braking distance.

Conclusion: By 9 weeks, driving performance of patients who have undergone fixation of a displaced ankle fracture returns to normal baseline. Therefore, physicians may wish to caution patients not to return to driving after a right-sided ankle fracture treated surgically until 9 weeks after the operation.