What are the options for treating broken legs in horses?

Unfortunately its not uncommon to see broken fractured legs in horses. We often associate broken legs with sport horses and racehorses being injured in competition. But we also see them in riding and companion horses because of riding accidents or trauma in the field.
Traditionally a broken leg has meant euthanasia of the horse and this remains the case for horses who suffer breaks of the important long bones of the leg or those with some of joint fractures and so on. However thankfully we now have some options for fracture management.  

Why are broken legs such a problem in horses?
It seems somewhat absurd that an apparently trivial problem like a broken leg should be lifethreatening. After all broken bones are readily fixed in cats dogs and humans. Unfortunately when we see a horse with a broken leg we are dealing with a number of factors that when put together can mean that keeping the horse alive isnt the right thing to do. 
Weight
Horses weigh a lot! Its difficult to find strong enough acceptable implants to repair the horses limb bones that can withstand enough stress whilst the break completely heals. This is not surprising given that surgery and implant placement involves a nervewracking often uncoordinated recovery immediately after the surgery. 
The horses mindset
No horse can understand that it needs to keep a broken leg immobilised nor that it must endure strict rest whilst the area heals. 
Fracture biology
A lot of fractures arent simple clean breaks and they may involve displacement of the fragments communication with a joint damage to blood supply and often an open wound. All of these take the fracture to a whole new level of complicated and severely worsen the prognosis for healing or return to normal life.
Return to function
The damage caused to the bone during the fracture the type of fracture and additional concerns like the stress put onto the other limbs which can lead to problems like laminitis can all mean a high level of uncertainty when considering the horses prognosis athletically even if the break does heal. During the recuperation phase the musculotendinous structures of the injured limb also change. It often becomes weaker affecting how the horse uses the limb. 
Physiotherapy and physical rehabilitation is important to try and maximise the function of the broken leg. But its no guarantee that the horse will have the same mobility or agility as before. This is why it often ends the careers of sports horses.
Its also possible that despite fracture management and time he may suffer