ABNORMAL CONDITIONS OF THE SHOULDER JOINT. 



587 



By the coraco-acromial vault we mean a 

 concave surface, looking downwards, formed 

 internally by the coracoid process, and ex- 

 ternally by the acromion ; the intervening 

 space being filled up in front by the proper 

 triangular ligament of the scapula, and com- 

 pleted behind by a portion of the under-sur- 

 f'ace of the acromial end of the clavicle This 

 coraco-acromial arch in the normal state 

 overhangs much the head of the humerus, 

 and its inferior surface is not articular, but, 

 on the contrary, is separated from the head 

 of the humerus, which is beneath it, by an in- 

 terval of about three or four lines, measured 

 in vertical height. This interval is normally 

 occupied by the long tendon of the biceps and 

 the capsular ligament, as they pass from the 

 upper margin of the glenoid cavity to the hu- 

 merus the capsular ligament having above it 

 the tendon of the supra-spinatus, a special 

 bursa mucosa, much cellular tissue, and the 

 fibrous bands, which pass from the humerus 

 to the coracoid and acromial processes. 



Under the influence of the most usual 

 form of this disease, all these parts intervening 

 between the head of the humerus and the 

 coraco-acromial arch or vault are absorbed ; 

 and the superior extremity of the head of the 

 humerus at length comes into immediate con- 

 tact with the concavity of the arch. The 

 first effect of this morbid process in bringing 

 about the remarkable changes which we have 

 been describing, may be to cause the absorp- 

 tion of those tendons, viz. the supra-spinatus 

 and the long tendon of the biceps, which pass 

 over the head of the humerus, and which, by 

 virtue of their muscular attachments, restrain 

 within proper limits the degree of elevation * 

 which the head of the humerus is normally 

 susceptible of. When, however, these tendons 

 are absorbed, and consequently the muscles to 

 which they belong have lost all power of re- 

 pressing the humerus, the latter is then drag- 

 ged upwards, and its head being constantly 

 pressed against the under-surface or concavity 

 of the coraco-acromial arch, not only do the 

 processes of the scapula which form this arch 

 at length show manifestly the effects of fric- 

 tion, but the outer portion of the acromial 

 end of the clavicle does so equally. All 

 these portions of bone are rendered con- 

 cave, and are usually covered by a porcelain- 

 like deposit, corresponding to an analogous 

 polished surface which covers the convexity 

 of the summit of the humerus. In many cases 

 in which the shoulder joint has long been the 

 seat of this chronic disease, the acromion 

 process has been found traversed in the line 

 of junction of its epiphysis, by a complete 

 interruption of its continuity, as if fractured : 

 we say as if fractured, for we are convinced 

 that this solution of continuity of the acro- 

 mion process is not really a fracture produced 

 by violence, but a lesion, which so frequently 

 exists in combination with chronic rheumatic 



* If the long tendon of the biceps be dislocated 

 and thrown inwards over the head of the humerus, 

 the same effects will be produced as if it were ab- 

 sorbed. 



arthritis of the shoulder, that we are com- 

 pelled to look upon it, in these cases, as a 

 peculiar organic change, the result of chronic 

 rheumatic disease. We do not pretend to 

 account for the separation of the acromion 

 process into two portions ; nor can we say 

 why it is that the division usually occurs in 

 the original line of the epiphysis, particularly 

 at the late period of life at which we generally 

 witness this phenomenon. In some of these 

 cases we have found the acromion in a state 

 of hypertrophy ; in others in a state of atro- 

 phy ; but in no case did there seem to be any 

 attempt at ossific deposition on the contigu- 

 ous surface of the separated portions of the 

 acromion, a circumstance which might be ex- 

 pected if a fracture had occurred. 



The glenoid cavity of the scapula, under the 

 influence of this disease, is generally much en- 

 larged ; and by becoming wider above, it loses 

 much of its ordinary ovoidal figure, approach- 

 ing in its outline more to a circular form. 

 The surface of the cavity appears preternatu- 

 rally excavated, its brim being elevated into a 

 sharp margin. The cartilage of incrustation, 

 as well as the glenoid ligament, are generally 

 removed altogether, some parts of the surface 

 are porous, and some covered with porcelain- 

 like enamel. Near the margins of the glenoid 

 cavity, where the capsular ligament arises, we 

 may often find osseous productions attached 

 to the capsular ligament, adding depth to 

 the receptacle for the enlarged head of the 

 humerus. The glenoid cavity will of course 

 be found to present much variety of form. 

 Sometimes the head of the humerus occupies 

 its upper portion, and habitually remains in 

 contact with the under surface of the acro- 

 mion and coracoid process, thus leaving the 

 lower part of the glenoid cavity unoccupied. 



Sometimes part of the head of the hume- 

 rus remains within the glenoid cavity, while 

 the remaining portion of it occupies the neigh- 

 bouring part of the subscapular fossa. Occa- 

 sionally the head of the humerus will be 

 found to have descended on the axillary mar- 

 gin of the scapula * ; while in other cases 

 equally rare, which we shall hereafter have 

 occasion to refer to, the head of this bone 

 may, under the influence of this disease, pass 

 backwards on the dorsum of the scapula: 

 under all these circumstances, the glenoid 

 cavity must undergo special changes of form 

 adapted to each variety. 



Those who carefully study the anatomical 

 characters of chronic rheumatic arthritis of 

 the shoulder, cannot fail in the course of their 

 investigation to observe many deviations from 

 the normal state of the joint, the result of this 

 disease, which are well calculated to mislead 

 those who are unacquainted with it ; to which 

 we may here advantageously advert. 



It has been repeatedly remarked, that one 

 of the most constant anatomical observations 

 we had to make in post-mortem examinations 

 of the shoulder joints of those who had been 



* Catalogue of the Museum of the College of Sur- 

 geons, Dublin, vol. i. p, 399. Prepar. E. b. 905. 



