Kiera Ward, 17, takes a daily cocktail of 39 painkillers for the excruciating pain - even though the fracture is fully healed and the pain is all in her head.
She broke her foot during a playground game of tug-of-war aged 11 but doctors believe the trauma of delays in her treatment triggered a condition called Complex Regional Pain Syndrome (CRPS).
The ailment causes her brain to experience phantom pain as if the injury is still there - and Kiera lives in excruciating pain 24 hours a day.
She said: 'The pain is unbearable, I can't describe to anyone else how it feels.
'There are so many days where I can't get out of bed or where I'm with my friends and I just burst into tears because I can't take it any more.
'The hardest thing is that my foot isn't hurt, my brain is just telling me it is. There's no reason why this is happening.'
Kiera broke her heel bone in September 2004 on a school trip to Kilbowie, near Oban.
She was playing tug-of-war when she fell under a group of classmates. No one realised she was badly injured until two days later when she could not walk.
The schoolgirl was taken to hospital, where doctors did not X-ray her but said she had ligament damage and sent her home with instructions to rest and take ibuprofen.
Two weeks later, she was in such pain her parents took her to Wishaw General where the fracture was found.
The delay in her treatment could have sparked Kiera's condition, which sometimes affects young, sporty girls for reasons no one understands.
She should have been off her crutches after six weeks but instead could not walk for 18 months.
It was not until September 2005 that doctors at Yorkhill Children's Hospital in Glasgow finally diagnosed Kiera with CRPS.