The extensor indicis proprius was used to restore mobility to a variety of hand movements in 27 patients. Retained independent index finger extension was obtained in a majority of patients postoperatively. Potential postoperative complications of index extension lag and deviation may be avoided if the extensor indicis proprius is sectioned immediately proximal to the dorsal hood. A corresponding laboratory study was undertaken to better define the anatomic constraints limiting independent finger extension. Distinct differences between juncturae tendinum and extensor compartment musculature help explain why the index finger may function as a relatively independent unit.