Horse circumducts hind leg

I was just researching hunter bump because the saddle fitter thought their might be a problem.Found out that its Very very hard to diagnosis but one of the criteria was circumducts hind leg.Remember soft tissue damage won’t show on testing, blocks can help but not if its SI.
I did have a 24 yr old who started doing this after a lifetime of occasional locking stifle issues , none that stopped her being ridden and sound.I. did some X-rays and injections.
Injections helped for about 6 months then quit working so she’s now living free in the pasture.She still favors that leg especially in winter.

Would someone please explain “10s”? I’ve never heard of that…
Txs!

Would someone please explain “10s”? I’ve never heard of that…
Txs!