An implantable internal dynamic splint device that replaces or augments the function of a muscle that is antagonized at a joint by a functional muscle is described. The device comprises an elastic body, a first tissue-attaching component adapted to be attached to a bone, and a second tissue-attaching component adapted to be attached to a bone or a soft tissue. Also disclosed is a method for treating muscle function deficiency using the internal dynamic splinting device. The method comprises the steps of making an incision at a target site on a subject, attaching the first tissue-attaching component of the internal dynamic splinting device to a first bone, attaching the second tissue-attaching component of the internal dynamic splinting device to a second bone or a soft tissue, and closing the incision. A method for compensating muscle function deficiency on a side of a joint using the device is also disclosed.
