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Hands on the steering wheel, one foot toggling between brake and pedal, head twisting to check mirrors. Consider the many bones and joints you must engage before you even turn on a car’s ignition, among them the fingers, wrist, forearm, elbow, shoulder, neck, heel, ankle and leg.
If you’ve recently had an injury to any of them, when is it safe to resume driving?

It turns out there are no widely accepted return-to-driving timelines for patients who must wear casts, slings, neck collars or controlled ankle-motion boots. Whether someone is recovering from a sprain, fracture, bunion surgery, knee or hip replacement or neck fusion, the ability to steer, glance at mirrors and brake safely can be seriously, if temporarily, impaired.

Several recent articles have attempted to summarize the disparate findings of a relative handful of postoperative driving studies. Among their conclusions: most studies say that braking function returns to normal four weeks after right knee arthroscopy, nine weeks after surgery for an ankle fracture, and six weeks after the patient can walk unencumbered after a fracture of a major lower-body bone. After a total right hip or knee replacement, the recommended time before driving is generally four to six weeks.

One absolute: patients should not drive with a cast or brace on the right leg, or if a cast or sling immobilizes the wrist or elbow.

The goal of such studies, which typically measure how long it takes a recovering patient to make an emergency stop, was to encourage surgeons to have conversations with their patients about factors to weigh before getting behind the wheel — something many surgeons are loath to do because of a misperception that they could be sued if the patient got into an auto accident or if driving somehow aggravated the injury. And even when surgeons do have that conversation, some of the research showed, many patients dismiss the advice.

“As surgeons, we can’t clear someone for driving, but we can educate them,” said Dr. Geoffrey S. Marecek, a co-author of one review, recently published in The Journal of the American Academy of Orthopaedic Surgeons. “I tell patients, ‘No immobilization, full range of motion without pain, and then we’ll talk about it.’”

“But that’s common sense and not science,” added Dr. Marecek, an assistant professor of clinical orthopedic surgery at the University of Southern California Keck School of Medicine.

Still, there is great variation among studies in terms of timelines and precautions, with one concluding that patients who were pain free could drive as soon as one week after a simple right knee arthroscopy. Experts therefore urge surgeons to tailor their advice to the individual patient and procedure, weighing such factors as the patient’s pain tolerance, medications, postoperative mobility and mental acuity.

One reason formal guidelines have not been endorsed by associations of orthopedic surgeons is that gold-standard data is scarce. Typically, the few studies used computerized driving simulators or obstacle courses and healthy volunteers (police recruits, in one), whom they fettered with mobility-restricting casts, splints and slings.

These are not representative recreations of the typical patient after surgery, but they do show that even pain-free, unmedicated, highly competent drivers experience lag time in braking when wearing such post-surgical supports.

Another limitation of the studies is that the vast majority were done on automatic transmission vehicles, and looked at impairments to right arms for steering and right legs and feet for braking and accelerating. Almost none looked at stick-shift drivers, who typically use both feet.

Dr. Kenneth A. Egol, vice chairman of the department of orthopedic surgery at N.Y.U. Langone Medical Center, who has conducted driving-impairment studies but was not involved in the recent review articles, noted that even on automatic transmissions, some people drive or steer with their left arm, or use their left foot because of an amputation or other medical challenges. Some drive cars with adapted hand controls.

“It’s all about what you’re used to,” he said. “The message should be, ‘if there is any impairment to your normal mode of operating a vehicle, you shouldn’t do it.’ ”

He said that normal braking function usually follows the patient’s return to walking, though other factors may play a role. If, for example, a patient is sleeping poorly because of pain, alertness may be a compromising factor.

Dr. David Goodwin, a resident physician in the department of orthopedic surgery at Georgetown University Hospital, and a co-author of a review recently published in the journal Orthopedics (PDF), typically instructs patients, “It’s best that you practice in a parking lot or another large open space.” But, he added, “Legally, I would never put down in writing that ‘you’re cleared to drive.’”

Many doctors remain skittish about even broaching the subject, with one study showing that 35 percent of surgeons never discussed safe postoperative driving with their patients.

But the doctors’ fear of litigation may be overblown. Dr. Marecek noted that many insurance companies and law-enforcement officials place the responsibility for the decision to drive squarely on the patient.

According to Julian L. Rivera, a partner at the law firm Husch Blackwell and a member of the American Bar Association’s health law section, “I know of nothing definitive in the law that establishes a standard for physicians in clearing patents for driving after orthopedic surgery.”

“Given that reality,” he said, “it is wise for physicians and patients to have a conversation about when it would be safe for the patient to drive.”