1. Complete dislocation of the acromioclavicular joint may occur with, or more often without, gross rupture of the coracoclavicular ligaments. The normal excursion of the conoid and trapezoid ligaments permits dislocation when the joint alone is involved.
2. Calcification and ossification, observed with the aid of soft-tissue roentgenographic techiniques, were found in the region of the conoid and trapezoid ligaments in approximately half of this series of forty-one cases. This phenomenon may be interpreted as a part of the process of healing of the ligaments.
3. The possible anatomical variations from the supposed normal joint structure may determine the success or failure of conservative treatment and the incidence of sequelae.
4. Improved methods of conservative treatment may be expected to correct the deformity and relieve symptoms in approximately 80 per cent. of the cases of complete dislocation of the acromioclavicular joint. In the remaining 20 per cent., deformity, pain, or limitation of motion may indicate the need for additional treatment by surgical measures.
5. A modification of the splints devised by Diliehunt, Howard, Shaar, and Legg is capable of overcorrection of the deformity, which is the key to success with conservative measures.
6. The chief obstacle to effective conservative treatment is interposition of soft parts,—such as meniscus, frayed capsular ligament, and flakes of articular cartilage between the joint surfaces.
7. Excision of the outer end of time clavicle, used successfully in nine cases in this series, is apparently the most uniformly successful method of treatment for both recent and old complicated acromioclavicular dislocations.
8. Two observations of possible diagnostic and prognostic importance were noted in the course of the study, although the limited number of cases does not permit positive statements concerning them at this time: (a) An increase in the width of the joint space on the injured side, demonstrated roentgenographically, indicates posterior displacement of time outer end of the clavicle, even when the acromion process and the clavicle are correctly aligned. (b) Palpable posterior displacement and abnormal mobility of the outer end of the clavicle, after three weeks of healing, indicate time probable failure of conservative methods and the recurrence of the dislocation.