To cast or not to cast, that is the question.
It seems there are a lot of very different treatments for broken bones. What gives?
In broad strokes, broken bones like to be lined up and held still for a month or two to heal. Joints, in general, like to be kept moving. The joint capsule is made of collagen, much like scar tissue. This tissue tends to shorten if not stretched out regularly. This means the joint will be stiff and lose range of motion when immobilized.
Most broken bones involve some joint injury, so there is always a trade off between the joints wanting to move and the bones needing to stay still.
Some fractures stay still enough to heal without a cast or surgical plate. Ribs run parallel to each other, so a fractured rib is supported by the ribs on each side. We also don’t put a bunch of pressure on our ribs, so they heal easily. Breaking a long bone in the foot (metatarsal) also heals with just the support of the bones on both sides.
Many joints will tolerate six weeks of immobility from casting. Ankle fractures and wrist fractures commonly immobilize the broken bone with a cast, and these joints get moving pretty quickly when out of plaster. This only becomes a problem if the joint has a lot of arthritis. Then even the ankle or wrist gets pretty stuck after casting.
There is another reason that ankles and wrist fractures are more often casted than surgically plated. These areas have little tissue surrounding the bone. The cast can be molded easily to keep the bones immobile and straight. Contrast this with a fracture of the thigh (femur). Because the thigh bone is surrounded by very bulky muscle, the bone can’t be held straight with a cast around the thigh. That is why broken femurs are always surgically fixed (with a rod down the middle of the bone).
There are other joints that don’t do well with immobilization. The two most common examples of this are the elbow and the shoulder. Immobilize a bent elbow for 6-8 weeks and you may never get it straight again. For that reason, some elbow fractures are simply put in a sling to keep the elbow moving. Shoulders also tend to develop adhesive capsulitis if not raised for four weeks. Even a healthy shoulder will scar if not raised for four weeks. The lesson: if your shoulder hurts, make sure you raise your elbow to your ear every day.
There are considerations to make in every fracture as to the best treatment. The key is to make sure the broken bone is held straight with little motion, while not making a bad joint from the prolonged lack of movement.