The pathological condition, therefore, of the different tissues which enter into the com position of the shoulder joint, as they are af fected in the early stages of this chronic dis ease, is as yet, we believe, but little known. The most remarkable features of the second stage of chronic arthritis of the shoulder joint we notice, is the descent of the head of the humerus from the glenoid cavity, and conse qnent elongation of the upper extremity of the affected side. This, we conjecture, may be accounted for by recollecting that the del toid and articular muscles, which in their normal state maintain the head of the humerus close up against the glenoid cavity, are now in a state of atrophy. They have from want of use, and perhaps, also, from sympathy with the dis eased state of the articular structures, lost all tonic force. Although these muscles are not really paralysed, still they seem not to have power enough to resist the influence of the weight of the upper extremity; and hence the head of the humerus, unrestrained by the naturally loose capsular ligament, descends to the extent of half an inch or an inch from the glenoid cavity: There can be but little doubt, also, that in the second period of the disease we are now considering, an effu sion takes place into the interior of the syno vial capsule of the joint : this may be altered synovial fluid or lymph, or purulent mat ter to a small amount ; but whatever the effusion be, it also will have the effect of par tially displacing, and causing an elongation of, the upper extremity.
It may be asked how it happens that the head of the humerus, °Dee partially displaced downwards, does not become subjected to a secondary displacement inwards, under the influence of the contractions of the pectoral and other muscles? The answer may perhaps be, that, in the second stage of this disease, the long tendon of the biceps retains its form, place, and functions so long as this tendon remains in its state of interrrity, arching over the head of the bone, antrthen passing in a perpendicular line down along the humerus, the head of this bone cannot be partially ele vated above its normal situation, nor even drawn inwards or backwards by either of the great muscles which form the anterior or pos terior walls of the axilla; but when the long tendon of the biceps is destroyed, as it very generally- is in the third stage of this disease, then the head of the humerus 'nay be moved in whatever direction the inclination of the new plane formed by the altered surface of the glenoid cavity may give, or the muscles inay draw it in.
In the third stage of chronic arthritis of the shoulder, the bones which compose the joint are carious, and their surfaces are partially and unequally- removed ; the length of the ex tremity may be diminished. The long tendon of the biceps is removed, and hence no longer influences the position which the head of the humerus is ultimately to take, whether the bone in this third stage be partially displaced upwards, forwards, or backwards.
Some of the surrounding muscles are in this period of the disease in a state of atrophy,. while others retain their form and functions. The proper articular muscles, whose normal function it is to keep the head of the humerus close to the glenoid cavity, are, in the third stage of disease, wasted ; and besides, as their capsular attachment is usually in this advanced stage of the disease destroyed, their influence becomes annihilated.
The pectoralis major rnay draw the head of the bone towards the median line ante riorly ; the latissimus dorsi and triceps pos teriorly towards the dorsum of the scapula; and several muscles, such as the attenuated deltoid, the coraco-brachialis, Szs., may ele
vate the head of the humerus, so as to bring its upper surface into contact with the acro mion and coracoid process.
We cannot pretend to say what it is which determines the line of direction the head of the humerus in these partial displacements which occur from disease may take,or explain why the bone should in some cases take one direction, and why occasionally another ; no more than we can assign any cause for the various direc tions the head of' the femur takes in the third stage of scrofulous caries of' the hip joint, a disease we consider analogous to this we are now considering.
Anehylosis of the shoulder joint. losis of the shoulder joint may be observed to be one of the terminations of an attack of acute or chronic arthritis of this joint. It may, we think, be remarked generally as the result of true bony anchylosis of any of the joints of an extremity, that shortening of the limb shall have taken place. This observation seems to be exemplified by what we commonly observe in studying the characters of true bony anchylosis of the shoulder joint. Most of the specimens preserved in our collection at the Richmond Hospital museum and else where, present examples of solid union of the bones which compose the shoulder joint ; partial displacement upwards of the head of the humerus, and slight shortening of the ex tremity having previously taken place. There is at present in the museum of the Richmond Hospital a specirnen of complete bony anchy losis of the shoulder joint, which was exhi bited by Dr. R. Srnith to the Pathological Society on the 13th March, 1841, along with some other examples of anchylosis of this joint. " The specimen," observes Dr. Smith, "was taken from the body of an individual aged 90, who had been confined to bed for many yearssbefore his death. The external appear ance of the shoulder joint resembled some what those of luxation of the head of the hu merus into the axilla, so far as the acromion process having been prominent, and the joint in the region of the deltoid completely flat tened; the arm was rotated inwards ; the glenoid cavity and head of the humerus formed one continuous bone ; the greater tubercle was anchylosed by bone to the acro raion process, while the coracoid process was similarly joined to the lesser tubercle." Consequently the humerus must have been partially displaced upwards, and the arm shortened. The supra-spinatus and infra-spi natus muscles, as well as the subscapularis, had undergone fatty degeneration froin want of use ; a change very commonly observed in cases of true anchylosis of long standing, no matter which of the joints has been the seat of this termination of arthritis. In the ex ample just adduced the humerus was observed to have ascended, and the greater and lesser tuberosities had formed a solid union with the coracoid and acromion process ; but in some examples the anchylosis has been found to have taken place directly between the sur face of the glenoid cavity and the head of the humerus ; and a vertical section of the bony structures running through the consolidated joint exhibited the cells of the original head of the humerus and the diploe of the scapula freely communicating with each other, just as we have already noticed as exemplified in 'complete bony anchylosis of the hip joint (see Vol. of this work, p. 796.). It may not be uninteresting to transfer our attention from the appearances disclosed by the post rnortem examination of an anchylosis of the shoulder joint to the signs by which we re cognise this state of the articulation in the living.