Common lower leg injuries?
bone spavin
bog spavin
bone chips
bowed tendon
bruised heels
brushing
bucked shins/shin splints
capped hocks & knees
check ligament desmitis/sprain
cross firing
curbs
filled/swollen legs
grease heel/scratches/mud fever
jack & knee spavin
osselets green & true
over-reach
ringbone
rundown
sesamoiditis
speedy cuts
splints
sprained ankle
sprained suspensory ligament
stocking up
suspensory ligament desmitis/sprain
thoroughpin
wind puffs/wind galls
Injuries/sores of the hooves:
abcess
bruised toe
corns
cracks/chips
laminitis
navicular
seedy toe/white line disease
thrush
I'm sure there are more yet...
Overreaching, where the hind hoof gouges a chunk out from the back of the fetlock/pastern.
Tendon injuries such as sprains and rips. You'll notice swelling and lameness immediately. These also require box rest and cold treatment. A scan can measure the extent of the damage. In the worse cases they can take months to heal and constant veterinary attention.
Windgalls are swellings around the top of the fetlock joint. It looks puffy and feels slightly warm, but the horse isn't particularly lame from it. You tend to notice these more with heavy horses or with horses that do alot of work on hard ground.
I can't think of anything else off the top of my head. I've probably missed some crucial ones.
I put this site in my bookmarks the other day because I thought it would be helpful. Hope it will be for you, too.
It discusses more conditions than there really is room here to do.