1. Osteosynthesis by the medullary route respects the three great principles of treatment of fractures,—reduction, fixation, and mobilization. Reduction must be excellent, since the introduction of the pin requires anatomical continuity of the bone canal. In fixation, the pin is very strong and firm, and assures a powerful immobilization of the fragments. Since it takes hold through the entire diaphysis, the forces of torsion and flexion are diffused over a wide area. Moreover, the presence of the foreign body in the soft bone accelerates the formation of callus. As to mobilization, the use of the limb is recovered rapidly; axial pressure favors osteogenesis and active movements avoid articular stiffness, muscle atrophy, and circulatory disturbances.

2. Experience acquired by us in fifty-five operations has demonstrated the relative simplicity of the method. It is an advance over the other procedures in present use in the treatment of diaphyseal fractures of the most important long bones of the skeleton. These procedures, in order to be successful, require either exceptional skill on the part of the surgeon or great patience and discomfort on the part of the patient. On the other hand, the method is not attended by the serious dangers which we mighmt have anticipated from the theoretical critics.

3. We have described the technique which is recommended for each area, and we have pointed out the difficulties which have been surnounted, as in the application of any new surgical procedure.

4. The results obtained in twenty-three diaphyseal fractures of the fenmur, ten of the leg, nine of the humerus, and thirteen of the forearm have been analyzed critically. We have outlined the operative indications. We do not advise intramedullary pinning in cornpound fractures. We recommend it enthusiastically in closed fractures, especially of the femur and of the forearm, where this method gives the solution of a problem not met satisfactorily up to the present time.