Hi Physiobob
Botox is definitely something to consider but there are a few things to think through before referring on. I take it you are finding velocity dependent resistance to passive dorsiflexion. (ie spasiticity). I presume he also has some contracture - almost bound to be. the botox will only work when the spasticity is really a very marked component in contracture. Just be aware that resistance through range is often mistaken for spasticity when it is in fact due to structural shortening of the musculotendinous unit. Contracture has been found to be the big factor in most cases of spasticity. When you do the quick PROM test if the catch and/or resistance comes on early in the range and when you repeat the movement slowly you don't elicit the response that may indicate a big spastic component.
If spasticity is a key feature then yes Botox may help but one should also think that the botox is a supplement to the physio to letngthen the MT unit and establish heel-toe walking. If serial casting is out of the question AFOs that can be adjusted during the day and resting splints at night that aim to maintain the increased extensibility during the night may help but it should also include physio aimed at avoiding the toe walking. resting splints and night can often be well tolerated as if they are well fitted they can be quite comfortable and light. Botox will only temporarily reduce spasticity (1-3 months max) and will not deal with the contracture problem or the motor control issue. I think you would need to do something more than just lowering the heel over time. What are resources like for orthotics etc? Often such treatment is quite fiddly and adjustments need to be made. And what about the skill of the Specialist? Botox injections are very much an "art" and badly delivered injections can not only be useless but can do harm. the injection should be with a needle wired to an FES unit to stimulate the muscle and guide the needle to the maximum number of neuromuscular junctions that can be knocked out.
Of course "toe walking" can also have nothing to do with spasticity. As I am not a paediatric physio I may be speaking a bit out of turn here - but children with "low tone" may result to over activating their plantar flexors to improve their power in walking - (apologies to the paediatric physios if that is a really bad description). In which case such treatment is completely misguided.
Hope that is of help - I am more an adult neuro physio so paediatric physios feel free to correct or add to what I have said.