I sprained my index finger really badly playing baseball. All the doctor did was tape it to the middle finger. How is that going to help anything?
Taping one finger (or toe) to another is called buddy taping and is a common treatment for ligament tears alongside the joint. These ligaments are called collateral ligaments.
Buddy taping helps ensure proper healing and return of normal function. The good finger actually works like a splint for the injured digit. The patient is advised to keep the buddy tape on for three to six weeks depending on whether the finger is sprained or broken.
Buddy taping is often used to allow early motion in a joint. It's used instead of a cast or splint because of the ease of use. It can be removed for bathing and put back on right away.
Christopher J. Hogan, MD, and James A. Nunley, MD. Posttraumatic Proximal Interphalangeal Joint Flexion Contractures. In Journal of the American Academy of Orthopaedic Surgeons. September 2006. Vol. 14. No. 9. Pp. 524-533.