Ankle fractures may have implications for driving safety

Study findings suggest that patients with right ankle fractures should consider waiting nine weeks before driving again.

Issue: January 2003

TORONTO — Patients who undergo operative repair of right ankle fractures should be advised not to begin driving until nine weeks postoperatively, according to a study which made use of a driving simulator to replicate real driving conditions.

Kenneth A. Egol, MD, of the department of orthopedics at New York University-Hospital for Joint Diseases, said that devising driving guidelines as postoperative protocol is an important yet sometimes overlooked task for orthopedic surgeons.

“People ask me all the time when they can drive after surgery,” Egol said. “I tell them now to wait nine weeks. If they insist on driving before that, I tell them that if they get in an accident, I am not clearing them to drive. I think that most people are OK with that.”

Conditions simulated

Egol’s study, presented at the Orthopaedic Trauma Association 18th Annual Meeting, used a driving simulator with accelerator and brake pedals that were linked to a computer to calculate patient reaction to real-time driving conditions.

Eleven patients between the ages of 20 and 70 with no systatic disease, no neurological condition, no history of lower extremity fracture or surgery, and a valid driver’s license comprised the control group.

The test group was composed of 31 patients who had undergone operative fixation of a right ankle fracture. The patients had been nonweight-bearing and performing active range of motion exercises for six weeks prior to the initial testing phase.

Patients were tested at six, nine and 12 weeks postoperatively. Egol said he used six weeks as the first test period because that interval was when they began bearing weight.

At the six-week mark, patients were seated in the simulator and permitted to adjust the seat for comfort. The seat’s position was recorded and duplicated at the remaining two testing periods.

There were three driving conditions simulated during each test: city, suburban and highway. Each trial lasted about 90 seconds. There were 18 randomly selected trials involved in the study.

During each test, patients were shown a computer image of a speedometer and watched specific target speeds flash in front of them. Patients then needed to increase or decrease force on the pedals depending on the target speed displayed.

Comparing results

The investigators collected Short Musculoskeletal Functional Assessment (SMFA) and ankle/hindfoot scores at six and 12 weeks and compared those with the results of the driving test.

There were three subparameters examined:

Initial response time — the time elapsed between presentation of the stimulus to apply the brake and the moment the subject initiated movement toward the brake pedals.
Foot movement time — the time elapsed between initiation of the movement to the brake pedal and the initial contact with the brake.
Brake travel time — the time elapsed between the moment of initial contact with the brake and the moment the brake pedal was released.

The summed parameters included brake reaction time, defined as the sum of the initial reaction time and foot movement time, and total brake time (TBT), defined as the time between the presentation of the stimulus and the moment that the brake pedal was released.

Significant difference in brake time

Brake reaction time was not significantly different in the ankle-fracture group at any time period. There was, however, a significant difference in total brake time. Mean TBT in the control group was 1009.58 milliseconds while in the study group, at six weeks, mean TBT was statistically significantly higher at 1273.68 milliseconds. It decreased to 1127.18 milliseconds at nine weeks and returned to near normal, at 1066.79 milliseconds, at 12 weeks.

Egol said those times translated to an increase braking distance of 23 feet (7 meters) assuming a driving speed of 60 miles per hour (96 kilometers per hour) at six weeks, an increase of eight feet (2.44 meters) at nine weeks and an increase of seven feet (2.13 meters) at 12 weeks.

SMFA scores improved significantly in all categories tested; however, no significant correlation was found between the SMFA subscores and the return of lower extremity driving function.

“We tried to take everything out of the equation except the patient’s feet,” Egol said. “We wanted to look at that one specific variable with driving as it related to an ankle fracture. This was very carefully done to give us a true view of patient response.”

For your information:

Egol K, Sheikhzadeh A, Moghtaderi S, et al. Lower extremity driving performance after ankle fracture. #29. Presented at the Orthopaedic Trauma Association 18th Annual Meeting. Oct. 11-13, 2002. Toronto.