Hi @Notgivingup (great username btw 
),
A warm welcome to the forum. 
There was research published in 2016 that suggests that severe head injury, which causes loss of consciousness, could be linked to increased risk of developing Parkinson’s which you can find more information on here - Understanding the link between head injury and Parkinson's risk | Parkinson's UK.
However, to my knowledge, there is no research to suggest that there is a link between an achilles tendon injury and Parkinson’s. There has been similar discussion on this topic on the forum before (Achilles tendonitis) , I’d recommend that you speak to his Parkinson’s nurse about this as the injury may be prolonged due to his condition. We have a free and confidential helpline that you can contact for further support on 0808 800 0303 or email us at [email protected].
Best wishes,
Reah
Forum Community Manager