The treatment of dislocation of the acromioclavicular joint (luxatio articuli acromioclavicularis, 1.a.a.) is a controversial issue. One of the reasons for this dispute is a persisting disagreement concerning the significance of the various structures influencing the stability of the joint. The present study, therefore. seeks to elucidate this subject by means of experimental clinical and radiological investigations of a post-mortem, human material. The normal anatomical structure of the acromioclavicular joint is depicted in Figure 1. The known variations of the joint as to the form and direction of the articular surfaces and the type of any possible disc have been investigated by other authors (Urist 1946, Moseley 1959,1969) and will not he discussed in the present study. The acromioclavieular ligament serves as a reinforcement for the joint capsule, its fibres connecting the upper edge of the clavicle with the upper edge of the acromion, some fibres being interwoven with the capsule. Some authors (Lanz & Wachsmuth 1959) have described a similar reinforcement of the lower part of the capsule, thus distinguishing between a cranial and a caudal acromioclavicular ligament ; however, they also stress that this is not a constant finding. Our study is, therefore, concerned with the proximal reinforcement only. In the same way, wc have not distinguished between the two parts of the coracoclavicular ligament, the trapezoid and the conoid part; for although each part has its separate function with regard to the ventral and dorsal mobility of the scapula, their clavicular function is the same, viz. to apply traction to the clavicle in a caudal direction (Urist 1946, Lanz & Wachsmuth 1959). In this study 1.a.a. is defined, clinically as well as
