Hi, I'm Dr. Jill. "Full thickness" generally means completely through the skin. The seriousness of a laceration completely through the skin on the cannon bone can vary greatly depending on the location, size of the laceration, and involvement of other structures. If the laceration goes into a joint on either end or the flexor tendon sheath on the back of the leg toward the fetlock, the injury would be very serious. Thankfully in the cannon region, though, there's lots of space without these structures nearby. If it's a large laceration involving loss of skin and exposed bone or additional trauma such as a bone chip, it would be important to keep the bone alive and deal with the wound appropriately. However, smaller lacerations that are easily closed with sutures with no other involvement of ligaments or bone are generally not at all serious and tend to heal well. It's important to bandage as needed and make sure the wound doesn't become infected, but most lacerations of the cannon bone that I see thankfully aren't at all serious and leave no lasting effects other than a scar. Also, young animals tend to heal quickly, so she has that on her side.

If you still have questions regarding the seriousness of your filly's exact laceration, I would recommend giving the vet that treated her a call since they've seen it and will be able to tell you exactly what they saw.

If there's anything else that I can clarify here, however, please let me know and I will be glad to offer whatever additional info I can.