6" scrape taking forever to heal, & there's a weird facet to this wound that I need an explanation for.?

On Oct. 1st, I was taking down this tree limb for the neighbor lady, & I didn't expect it to bounce back up, so I ended up with a 6" scrape on my shin bone. It was swollen for a month or so, & yes, I did go to the urgent care clinic when the swelling didn't go down after a week, complaining that it felt like there was a splinter under the skin. She gave me antibiotics & a tetanus shot, which made no difference. 4 mths later, I still have one spot that hasn't fully healed but the swelling has gone. The weird thing is, I can move the skin back & forth around the entire area, but that one spot, is stuck in place. What is that? Do I have a bone splinter that it has attached itself to?