doodah,
Tibia fractures are significant injuries, which take quite a while to heal. It is not surprising that he is a little slow at present. Once the fracture becomes "sticky" (where there has been enough osteoid laid down to "glue" the fragments together), it does not hurt as much. This usually takes about 10-20 days after injury.
He should be elevating the leg, with the foot way up in the air (above the heart level). He needs to wriggle his toes several times every hour he is awake. Both of these will help reduce the swelling in the limb. Moving the toes will also help reduce the chances of the tendons getting scarred down. It may be a little uncomfortable wriggling the toes the first few times, but it will become easier and easier.
In the current acute phase, he is going to note throbbing around the fracture when the limb is placed in a dependent position (hanging down). But, he is athletic, so he should not have too many troubles in starting to get up and move about some. While he should not be hanging the leg down for extended periods of time quite yet, he should start moving around.
He should have the upper body strength and coordination to be able to use crutches just fine. When he is resting though, the foot should be up in the air.
He should not really have a lot of pain around the injury site. Yes, it is going to be sore, but once a fracture is immobilized, so that the periosteum is no longer being stimulated, there really should not be a lot of intense pain. The periosteum is a thick sheath of soft tissues around the bone, which carries the blood vessels and nerves to the bone. So, again, while he will have some soreness and occasional throbbing, he really should not be in a lot of pain. If he is, that may need to be evaluated.
In terms of treatment, the indication for surgery is failure of nonoperative methods to treat a fracture. If the fracture is essentially nondisplaced and is in good alignment, then treatment in a long leg cast is the standard of care. Surgery does not make a fracture heal faster, in fact it can actually slow down the union of a fracture.
Once the fracture is showing signs of callus formation and has begun to unite, the long leg cast may be able to be cut down to a PTB cast. This is a patellar tendon bearing cast, which is a special type of short leg cast, which has special molding around the proximal tibia, so that rotation is controlled (the reason that a long leg cast has to be used at first). This will allow him to start working on knee range of motion. If the fracture is healing well (and the fracture pattern is one that is stable) he may also be able to start weight bearing some at that point (but every fracture is unique).
Your son is also sort of at that in between age, in terms of fracture treatment. Young kids rarely need to have tibia fractures surgically treated. There is also concern about damage to the growth plates in kids. At 16, your son may still have open growth plates.
So, while he has a ways to go in terms of recovery, he is athletic (and young) so he should not have too many problems. Once he gets the hang of how to move the cast, getting up and down, and the use of crutches, he should be tooling around with no problems.
One trick to move the casted leg when in bed is to hook the foot of the uninjured leg under the back of the ankle of the cast and use the good leg to power the moving of the casted leg. You then sort of pivot on the butt when swinging the legs over the side of the bed. The hands can be put on the bed for extra stability, as they do not have to be used to help move the casted leg. This technique can also be used when getting back into bed: sit on the edge of the bed (couch), hook the good leg under the cast, lean back, pivot on the buttocks as the good leg lifts up the casted leg, and swing the legs into bed. This takes a little practice, but is a great way to get in and out of bed.
In terms of healing times for tibia fractures, it usually takes about 10-13 weeks for a low energy tibia fracture to unite. That is just for bone healing and does not include time for rehabilitation. Your son may heal a little faster because of his age.
He should be eating a proper balanced diet, with some extra protein, calcium, vitamin D, and magnesium. Most of the time, these can be obtained through the diet, but a one-a-day vitamin could be used. Vitamin D is mostly obtained from sunshine, as food is a poor natural source (some foods are fortified). So, 10 to 30 minutes of sunshine on the face and arms is enough to get the full daily requirement for vitamin D. And, getting out of the house is also a good idea for sanity. Depression is common in patients who have a significant injury, so getting out of the house helps (even if it is to the back yard).
No smoking. This is the single most detrimental thing there is to fracture healing.
So, he should be feeling better day by day now. He should not be having a lot of intense pain. Yes, soreness and occasional throbbing is to be expected, but he should not be in agonizing intense pain. That may be a sign of something going on and should be evaluated. Eat a good diet, get some sunshine, wriggle the toes, keep the foot elevated and he should be on his way to healing and recovery.
Oh, one final note, he should not rest the cast on the point of the heel (either on the floor or in bed). Short times, such as when going to the bathroom, are okay. But, resting on the point of the heel can lead to pressure points, which can lead to pressure sores in the skin. When elevating the leg, place the pillows or pads under the calf over a broad area, so that the heel is hanging free.
Also, if your son is still taking opioid pain medication on a regular basis, this can cause significant depression of the faculties, sleepiness, being unstable when up on crutches, etc. These should be used if needed in the acute stage, but they do not need to be taken out of fear of developing pain. Patients with fractures tend to get better pretty quickly, especially the young one, and as a result the discomfort should decrease pretty steadily also.
Good luck. Hope your son does well.