Disclosure: my normal job is "physician". I am not an orthopedist but have some expertise in acute orthopedics and fracture care, mostly in the ER. I've applied a bunch of splints and casts.

We actually have pretty good evidence of fracture care going back to ancient Egypt at least, which had advanced medical care for the time and a lot of well-preserved bodies we can study now. Numerous mummies and other preserved remains have been found which show evidence of well-healed fractures of long bones. Fractures of the femur usually show signs of deformity, but those of the arm and forearm show good healing. This would indicate that splinting, rather than casting was used to support the bones in the healing process. (A splint is perfectly good for keeping bones aligned in a compliant patient. It won’t be quite enough to keep alignment in a weight-bearing bone, especially if its owner if forced to go back to work too soon as we would expect a peasant or a soldier to be.). One set of remains was found during the Hearst Expedition in which an adolescent male was found with a comminuted fracture of the femur (bone I'm multiple pieces). Four wooden splints had been applied, each wrapped in linen. A blood-soaked dressing was found directly over the fracture site, indicating that the bone break had punctured the skin. No evidence of bone healing was noted, indicating that the young man died shortly after the injury. Another specimen was found with multiple fractures of the arm with similar splints and dressings, indicating that this type of care was not unusual. No healing was seen, indicating that the victim died shortly thereafter. (In those days an open fracture was likely either an amputation or a death sentence, with few ways to ward off infection and gangrene in the exposed bone.)

Splinting of fractures remained standard medical care in most ancient cultures, with many of them having left written instruction behind. Hippocrates and Galen wrote of splinting and fracture care. A long passage from an Arab physician named El Zarawhi from around AD 1000 goes into great detail with a technique that is not far at all from what I was taught to do:

"Then put between the bandages enough soft tow or soft rags to correct the curves of the fracture, if any, otherwise put nothing in. Then wind over it another bandage and at once lay over it strong splints if the part be not swollen or effused. But if there be swelling or effusion in the part, apply something to allay the swelling and disperse the effusion. Leave it on for several days and then bind on the splint. The splint should be made of broad halves of cane cut and shaped with skill, or the splints may be made of wood used for sieves, which are made of pine, or of palm branches, or of brier or giant fennel or the like, whatever wood be at hand. Then bind over the splints another bandage just as tightly as you did the first. Then over that tie it up with cords arranged in the way we have said, that is with the pressure greatest over the site of the fracture and lessened as you move away from it. Between the splints there should be a space of not less than a finger’s breadth. "

Casting was also known to the Arabs of the time, probably drawing on prior Byzantine work. Various casting materials were proposed, including one made of lime and egg white that was “hard as stone and will not need to be removed until the healing is complete.”

These innovations ultimately made their way to European medicine. The English surgeon William Cheselden wrote of a fracture of his elbow sustained as a boy in around 1700:

“I thought of a much better bandage which I had learned from Mr. Cowper, a bonesetter at Leicester, who set and cured a fracture of my own cubit when I was a boy at school. His way was, after putting the limb in a proper posture, to wrap it up in rags dipped in the whites of eggs and a little wheat flour mixed. This drying grew stiff and kept the limb in good posture. And I think there is no way better than this in fractures, for it preserves the position of the limb without strict [tight] bandage which is the common cause of mischief in fractures.”

Casting materials of plaster were known and used by the Arabs, and these eventually made their way to Europe too, where they became standard. Most casts were, then as now, not applied for a few days after a break to allow for acute swelling to subside.

The next major innovation in fracture care would not occur until well after your historical injury, with the introduction of the plaster bandage in 1876 by the Dutch military surgeon Antonius Mathijsen. He wanted a dressing that could be applied quickly on the battlefield to allow immediate immobilization. He came up with a plaster-coated bandage that could be stored dry, then moistened and applied to an injured limb, where it would harden and set in place. Refined versions of the Mathijsen bandage are still in use today, although the fabric and plaster has mostly been replaced by air-curing fiberglass.

Let’s get back to your injury, or that of your Revolutionary War compatriot. Most ankle fractures are of the distal part of the non-weight-bearing fibula. A smaller number are of the larger and very much weight-bearing tibia. Any of the below scenarios will be a bit worse for a tibial fracture.

• A closed, simple fracture (one break, no exposed bone) would have been treated in much the same way it would be today – reduction of the fracture, initial splinting, followed by plaster casting. The big debate would have been over your convalescence, and whether or not it should include complete rest and healing or early ambulation. In all likelihood, ambulation would have been pressed if you were someone who was needed to work. If so, there were a variety of braces made of wood or metal that would have been used to support the broken bone, or crutches to allow you to move without bearing weight. A fracture of the fibula would likely have healed very well, of the tibia, probably less so. You might be left with some sort of limp or chronic pain depending on how well the bone had been set.
• If your fracture had been open (skin broken/bone exposed to air), you would likely have needed an amputation, due to either infection or the presumed threat of it. A dirty wound, such as in battle, would likely have been amputated in surgery on the spot.
• The in-between area would have been a closed but comminuted fracture (bone broken into multiple pieces but skin intact). In modern times, these usually get surgery and the placement of plates, screws, or the external fixation devices you see in hospital shows. These techniques were not available back then, so your injured 18th century man would have either dealt with a permanent deformity and limp or possibility have had an amputation done (more likely for a fractured tibia). These fractures just would not have healed well with the technology of the day.

Bibliography:

Orthopaedic Emergency and Office Procedures (Hoshino, Harris, and Tiberi) 2013

History of Fracture Treatment (https://musculoskeletalkey.com/the-history-of-fracture-treatment/)

Pfenninger and Fowler's Procedures for Primary Care (Fowler et al) 2019

Plaster of Paris–Short History of Casting and Injured Limb Immobilzation, Szostakowski et al, Open Orthopedics Journal 2017; 11: 291–296