LUXATION. 



tile inferior ; a third, -the intemal ; an3 a fourth, the ex- 

 ternal. 



It is manifeft, that the head of t!ie humerus cannot be 

 difplaced towards the upper edge of the glenoid cavity. In 

 that direftion the acromion and coracoid proceffes, the 

 triangular hgament ftrctched between ihem, the tendons of 

 the biceps and fupra-fpinatus, and the fiefliy part of the 

 dehoid mufcle, form an effeSual refillance to any force pro- 

 peUing upwai-ds the head of the bone. Suppofing a luxa- 

 tion in this direftion were to happen, the head of the bone 

 mull alfo be pulhcd outwards, a thing which is impoffible, 

 becaufe the trunk hinders the elbow from being inchned far 

 enough inwards for that puipofe. 



On the other hand, the three remaining edges prefent but 

 little refiftance. At the lower one, the long portion of the 

 triceps ; at the internal one, the tendon of the fubfcapu- 

 laris ; and at the external, the tendons of the infra-fpinatus 

 and teres minor; eafily yield to a force direfted againll 

 them, and admit of primitive luxations taking place, eitlier 

 downwards, inwards, or outwards ; downwards, between 

 the tendon of the fub-fcapularis and that of the long head 

 of the triceps; inwards, between the fub-fcapulary mufcle 

 and fofla ; and outwards, between the infra-fpinatus mufcle 

 and fubjaccnt part of the fcapiila. All thcfe modes of dif- 

 placement do not occur with equal frequency, as will be 

 prefently confidered. 



After the head of the humerus has quitted the glenoid 

 cavity, and flipped in one of thefe three direftions, it often 

 clianges its iituation again ; and, in this event, a confecutive 

 luxation may follow a primitive one, either downwards, or 

 inwards; but never that outvvards, were fuch a cafe to oc- 

 cur, becaufe the fpine of the fcapula would prevent it. 



According to Default, a confecutive kixation inwards may 

 fucceed a primitive one downwards, as there is nothing to 

 liinder the head of the bone from palling between the fub- 

 fcapulary mufcle and folfa. On the contrary, Ihould it 

 tend outwards, the tendon of the triceps refifts, and, not- 

 withftanding the flatement of Petit, a confecutive luxation 

 in this laft direftion never happens. 



Sometimes, when the head of the humerus has efcaped at 

 the internal or inferior part of the capfule, it is carried be- 

 hind the clavicle, fo as to form a confecutive luxation up- 

 wards, a cafe which was noticed by Pare, perhaps by Galen, 

 and a fpecimen of which was preferved in Default's raufeum. 

 Here the feccondary difplacement only takes place Howly, 

 and after it has happened, art can feldom correft it, on ac- 

 count of the firm adhefions contradlcd by the furfaces of 

 the bone. Thus, in the example referred to, a new cavity 

 was formed behind the clavicle, and the humerus was con- 

 nected with the furrounding part by a kind of new liga- 

 ments. 



From this ftatement, derived from Default, it follows 

 that the humerus is fubjedl to four forts of difplacement : 

 I, downwards; 2, outwards. In thefe directions the diflo- 

 cation is always primitive, c* Inwards, which may be either 

 primitive or confecutive. 4. Upwards, in which direftion 

 the accident can only happen confecutively. As Default 

 obfei-ves, the fecond and the fourth cafes are exceedingly 

 rare, compared with the reft. 



Primitive Luxations. — Thefe are caufed by falls or blows 

 on the arm, and the kind of diflocation appears to be deter- 

 mined by the pofition in which the limb happens to be at 

 the moment of the accident. 



If the arm is more or lefs raifed from the trunk, without 

 being inchned either forwards or backwards, and the patient 

 fills laterally, the weight of the body, being almoft entirely 

 fupported by the humerus, forces downwards its upper end. 



which lacerates fhe capfular ligaments, and 19 diflocate^ 

 downwards. The occurrence is alfo in part facilitated by 

 the united action of the latilTimus dorfi, peftoralia major, 

 and teres major mufclcs. Thefe are in a (late of involun- 

 tary aftion, and tend to draw downwards the head of the 

 hum.erus, while the elbow remains fixed on the ground or 

 furface againft which it has fallen. Some authors believe, 

 that a violent contraftion of the deltoid mufcle may alfo 

 liave a (liare in luxating the fhoulder downwards, as it may 

 tend to force the head of the humerus through the capfular 

 ligament towards the axilla. Defat;lt thinks the truth of 

 this itatement is confirmed by many obfervations, and quotes 

 the cafe of a no'ary whofe (houlder was diflocatcd down- 

 wards, in lifting up -a heavy regiilcr book. 



The manner in which a primitive luxation inwards is pro- 

 duced, is little different from that of the foregoing cafe. 

 The elbow, at the moment of the fall or blow, is both fepa- 

 rated from the trunk and carrird hackivards. The weight 

 of the body acts upon the humerus, the anterior portion of 

 the capfular ligament gives way, and the head of the bone 

 is didocatcd forwards. 



The luxation outwards oan only be ocrafioned when the 

 elbow is inclined forwards, towards the oppofite fhoulder. 

 If the force is fufhcieutly great, the outer part of the cap- 

 fular ligament is lacerated, and tlio head of the humerus 

 difplaced. But, fays Default, what can fuch power be ? 

 In a fall, when the arm is forced againft tlie fide, it cannot' 

 be moved far enougli to caufe a laceration of the capfule. 

 Hence this eminent lurgeon concluded, that luxations of the 

 head of the humerus outwards muft be ^ry uncommon 

 cafes. None are recorded by furgical writers, and Default 

 himfelf had never obferved fuch an accident. Befides, it is 

 worthy of attention, that when in falls, the arm feparated 

 from the fide is inclined either forwards or backwards, the 

 weight of the body only operates upon it obliquely, and 

 it is little ai?ted upon by the latiflimus dorfi, peftoralis ma- 

 jor, and teres major mufcles. Hence no difiocati.ms of the 

 flioulder are fo frequeiit as thofe downwards, in* the pro- 

 duftion of which cafes the infijence of the weight of the 

 body, and of the action of the mufcles is direft. However, 

 the luxation inwards is not uncommon, and many of De- 

 fault's cafes prove the poiliLiility of a primitive diflocation of 

 this kind, notwithftanding feveral modern authors hnv9 

 doubted it, by believing with Hippocrates, that originally all 

 luxations of the ftiouider happen downwards. 



It fometimes happens, that the lacerated opening in the 

 capfular ligament fuffices for the pad'age of the head of the 

 bone from the glenoid cavity, but immediately afterwards 

 contracting, is not large enough to admit of its retuiti. 

 This practical faft was lirft noticed by Default, who lias 

 pubiiflied two examples of it in his journal. Such cafes 

 have ficce been very frequent at the Hotel Dieu, at Paris. 



Confecutive Luxations. — When a confecutive luxation fuc- 

 ceeds a primitive one, many caufe? may concur in producing 

 this change. If a fecond fail ihoidd happen, the elbow 

 being feparated from the fide, the head of the bone may* 

 eafily be forced out of the place into which it was firll 

 thrown. A cafe illuftrating this obfervaiion is related in 

 Les CEuvres Chir. de Default par Bichat, torn. i. p. 350. 



The adlion of the mufcles is a permanent caufe of a fre(h 

 difplacement. When the humerus is diflocated downward?, 

 the pectoralis major, and the inner portion of the deltoid, 

 pull its upper portion inwards and upwards. 



Various movements communicated to the arm may alfo 

 produce a change in the pofition of the luxated head of the 

 bone, according to their direftion. Thus a liuation in- 



