Coracoclavicular joints. Reflections upon incidence, pathophysiology and etiology of the different forms.

Since the first description of the coracoclavicular joint in 1861, many papers have been published reporting its occurrence, anatomical description, and geographical distribution. However, there are as yet no published articles with a convincing explanation for the rather variable forms of this variant. In this study, we investigated the occurrence of the coracoclavicular joint in the current and medieval population of Toulouse city and propose, through biometric measures, an explanation for the different forms of this anatomical variant. A total of 2192 chest X-rays taken for various conditions at a receiving hospital and 392 specimens (784 scapulae and an equal number of clavicles) of the L'Isle-Jourdain Series were examined with this aim. When present in the osteologic collection, the sizes of the articular conoid process as well as the height of the corresponding coracoid and acromial processes were noted. A coracoclavicular joint was noted in 0.82% and in 1.78% of the individuals examined in the radiological and osteologic series, respectively. The conoid process varied in size and correlated with the disposition of each correspondent coracoacromial arch. Osteoarthritis was noted in some of these joints when there was discordance between the conoid process size and the architecture of the correspondent coracoacromial arch, suggesting impingement. Our findings support a genetic origin for this variant, and suggest that its occurrence is also probably influenced by environmental factors. Osteoarthritis of this joint may be responsible for shoulder pain.