The positive thing about an outside splint is that it doesn't support as much of the horses weight as an inside splint.
There is a chance the splint may heal without medication or other types of treatment. However there is a need for medication if inflammation is present and/or if you chose, medication to prevent excessive growth. Surgery is only needed if the splint is actually interfering with the knee joint. It is best to have your vet xray the leg.
The website below will also indicate the information above and is informative regarding nutritional needs and management for equine splints.
http://www.equinesplints.com/splinttreatment.htm
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Oliver's Mom