A titanium cage replaced his C6 vertebrae and surgeons needed to fuse his C5 and C7 vertebrae together.
In the gruelling rehabilitation and recovery that has followed since, Willoughby's major motivation has been to stand on his wedding day.
The 26-year-old wore special locked-in knee braces to help him to stand and before December 31 that's all Willoughby was thinking about.
"I'm sort of able to shuffle out there a little bit, so that's the plan," Willoughby told AAP last week.
"That's been the last month I've been doing that every day. It's been a lot of work to get to that point.
"I'm just very happy that I'll be able to be vertical at the ceremony with Alise and just enjoy the day as much as possible."
Willoughby went one better on New Year's Eve, not just standing, but dancing with the "girl of his dreams".
It was a touching moment in a romance that has overcome plenty of speed bumps.
From not being able to move Willoughby has graduated to riding a stationary bike, crawling, kneeling and now standing and dancing. And during his 15-month ordeal Post has been right by his side โ like she has been since the pair met nearly a decade ago.
They first crossed paths in 2008 and Willoughby always knew Post was the woman for him.
"I always had a crush on Alise," Willoughby told NBC in 2016. "I would write her almost like a fan. She didn't reply that often, but I got a few replies."
Later in 2008 Willoughby moved from his home city of Adelaide to the States to pursue his professional career. He stayed with Post's parents in St Cloud, Minnesota while he trained and the two started dating.
They both reached the pinnacle of their sport, competing at the 2012 Olympics together โ but they left with vastly different results.
Willoughby ended his campaign on the dais with a silver medal around his neck but Post had no such luck, crashing in her semi-final heat. She tried to get back up after her rivals had already finished but couldn't manage it, and was helped to the line by two officials in heartbreaking scenes.
But those tears would be nothing compared to the family tragedy that struck in 2013. Post's mother Cheryl was diagnosed with melanoma and died in April the following year.
Post banished her London demons by winning silver at the 2016 Rio Games. Willoughby also competed in Brazil but missed out on a top-three spot in the final.
Their lives became about so much more than just riding after Willoughby's accident at his local track in September that year, but he's hopeful of brighter days ahead.
"I've already made gains that they said I never would and my ultimate goal is to be out of the wheelchair one day," Willoughby said.
If that does eventuate, Willoughby's mother Sharon is sure his new wife will be a large part of his success.
"They're just a remarkable couple together. The support and the energy they get from each other and the positivity is just amazing in itself," she told AAP.
"And their whole support network, rivals and friends from the sport. You never know how anyone is going to react and cope but you couldn't fault one of them."
- With AAP
