Gen I have just been through this exact same thing with a Furst Nymphenburg colt. If anything he was worse than yours. He was totally knuckled over on both front limbs.
I tried 3 lots of oxytet with little or no effect. Toe extentions were applied and he was splinted and wrapped like yours. We would cast his legs including the hooves, wait for them to set whilst holding the leg as straight as physically possible, and then cut them up the sides and remove them. We wrapped the leg with alternate layers of soft padding (soft ban) and crepe bandage and finished with encasing the whole lot with vet wrap. Over this we put the two halves of the cast back together and bound it on with vet wrap as tight as possible. There was a gap down each side of the casts due to the additional padding but very little movement in the limb.
He wore the casts for 18 hours a day. For the other 6 hours the hard casts were removed but the wraps underneath were left on. As soon as the casts were removed he would find it difficult to get around. Once I put the casts back on each day he would do his best to have a little run around.
He and his mother lived in an outdoor covered area against the barn wall (one and a half stables big) with a very deep but quite firm bedding of wood peelings. They were right in amongst the comings and goings of the yard and able to see plenty of things and other horses etc. They were in here for 3 months. Even with all the fresh air and very regular mucking out this got pretty yucky. Every 3 weeks I would dig all the bedding out down to dirt and replace it with totally clean fresh stuff. This was a hellish job but necessary to keep the environment as clean as possible.
We recast the legs 5 times in 3 months. And altered the toe extentions accordingly. At first there was so little improvement. He learned to carry his weight on his hind end and to do little pirouettes to get around. It was heartbreaking to watch but the vet and I were committed and the vet was sure it would come good in time. He was right!
The colt grew stronger and the limbs relaxed substantially but when the wraps were removed he would still knuckle over. The hard casts were eventually removed but the limbs were still wrapped for most of the day.
Just as I was getting pretty despondent about things one limb just āall of a suddenā had a good pastern angle. Once the pastern angle reaches a certain point the horseās bodyweight does all the stretching and physio for you and the progress from this point was phenomenal. The other limb relaxed shortly after. All of a sudden we were scrambling to remove the toe extentions and trim the toes back to assist breakover. It was such an enormous sense of relief!
Pressure sores. Yes, there were sores. At first the hair went a bit wrinkling and then fell out in clumps. One limb had superficial wounds around the leg under the knee and on the fetlock. The other limb had a much deeper wound on the front of the cannon beneath the knee. This wound was a real yucky mess. Fortunately the wraps were removed shortly after the wounds appeared. I had to wrap the bigger wound for a further 6 weeks to keep it clean and to stop him chewing at it.
Now he is 7 months old. His limbs are pretty close to perfect. Any misshappen hoof (from the toe extentions) has been trimmed off and they look excellent. There is some wrinkly hair from all the bandaging around the back of the fetlocks and a smattering of white hairs on both limbs. There is a small dry scab where the large deep wound was and some thickening of the skin around this area. He is completely sound and the first time I saw his spectacular trot I got a bit weepy 
There is barely anything to see from all the drama of the past months.
The vet has assured me that there will be no residual affects, his ability to perform and his ongoing soundness will not be compromised.
Can I send you some photos so you can post them here?
