LUXATION. 



only be made complete by the operation of a vaft force; 

 With refped to the orbicuhr joints, it is very different, as 

 few of them are fiibject to any diflocation, that is not com- 

 plete. If the head of the humerus, or thigh-bone, is forced 

 ■on the cartilaginous brim, furroundinjr the cavity deftined for 

 its reception, the round flippery ball only touches the part 

 on which it telts by a few points, and, thei-efore, either re- 

 enters its natural foclcet again, or flips entirely from it ; 

 in the latter event, of courfe the luxation is complete. 



But as M. Boyer has noticed, there are fomc articula- 

 tions which, though truly orbicular, are yet liable to in- 

 complete luxations. For iuftancc, the head of the aftra- 

 galus may be fo difplaced, as only to abandon, in a partial 

 manner, the cavity in the potterior furface of the os navi- 

 culare. However, in this example, the orbicular ligament 

 is tight, very ftrong, and the motion inconfiderable. I.aftly, 

 it may be obferved, with regard to the extent of difloca- 

 tions, that when the head of a bone is entirely thrown out 

 of the cavity, in which it is naturally placed, it may be forced 

 to a greater or lefs diftance between the intcrilices of the 

 imifcles. 



On the fubjcft of the different direftions, in which a bone 

 may be difplaced, we have to fta^c, that, in the round ar- 

 ticulations, it may be luxated in the direftion of all the 

 radii, which pafs from the centre of the circle formed by 

 the circumference of the articular cavity. In faft, there is 

 not a point of the edge of the glenoid cavity where the 

 humerus may not efcape. However, owing to particular 

 circumftances of conforn-ation, a luxation moilly takes 

 place in certain direftions, well afcertained by experience, 

 lb that the varieties of diflocations, diftinguiihed by the 

 courfe of the difplaced bone, are, as Boyer well explains, 

 much lefs numerous than might at firft be fuppofed. The 

 ter.Tis upwards, downtuards, forivards, lachivards, inward!, 

 and outivards, are frequently applied to luxations, as de- 

 BOting the direftion in which the head of a bone is 

 difplaced. Ginglimoid joints are generally fufceptible 

 of being diflocated only in the dire&ion of two line?, 

 namely, a tranfverfe one, and one extending from the front 

 to the back of the articulation. 



The length of time a diflocation has exifted makes a dif- 

 ference of the higheft importance, the difficulty of cure in- 

 creafing in proportion to the time the accident has been 

 left unreduced ; and, indeed, after a certain time, the re- 

 duftion becomes impradlicable. 



The foft parts and the bone itfelf have acquired a certain 

 pofition, and the ligaments and mulcles furrounding the 

 difeafed joint become ftiff, and yield with difficulty to the 

 efforts made to reduce the bone. If a certain number of 

 days have elapfed, the laceration in the hgaments may have 

 becom.e fo far clofed as to render the redutlion impoffible. 

 Laftlv, the head of the bone mav have become firmly ad- 

 herent to the parts, amongll which it has been forced. 



Luxations, in general, may be complicated with a greater 

 fcr lefs degree of contufion, with a wound or fracture, with 

 a rupture of a blood-veffel and confequent tffufion of blood 

 in the cellular fubftance, with contuCon of an important 

 ijerve, and a paralyfis of the organs to which it is diftributed, 

 &c. 



The following general account of the caufes, fymptoms, 

 prognofis, and treatment of luxations, is chiefly from Boyer's 

 lectures on the difeafes of the bones. 



The caufes are divided into external and internal ; "both are 

 predifpofmg or occafional. 



The predifpofition. to luxation may depend on circum- 

 ftances natural or aecidental. The natural are, the joint 

 admitting of great latitude of motion, the fmall extent of 



furfaces by which the bones are in contaft, the laxity and 

 fmall number of the ligaments uniting them, the weakiicfs 

 of one fide of an articulation arifmg, for inflance, from a 

 great notch on one fide, as is obferved at tlie interior and in- 

 ferior part of the acetabulum, difeafe, fuch as a paralyfis of 

 the mufcles, which furround an articulation, and a wcaknefs 

 and relaxation of its hgaments, may alfo occafion a pre- 

 difpofition to diilocations. In a paralyiis of the deltoid 

 mufcle, the weight of the arm alone has been known to pro- 

 duce an elongation and gradual relaxation of the capfular 

 litrament of the flioulder joint, and to remove the head of 

 the humerus two or three inches from the glenoid cavity of 

 the fcapula. Boyer has obferved in a child that laboured 

 under an atrophia of the mufcles of the arm, an empty 

 fpace of nearly an inch between the head of the bone and 

 the furface of the glenoid cavity, which could be dillinftly 

 felt through the emaciated deltoid mufcle. 



Sometimes the relaxation ot the ligaments appears witli- 

 cut any evident caiife, and gives fuch a difpofuian to lux- 

 ations, that they take place from the llighteil caufes ; fuch 

 was the cafe of a woman who could not yawn even mode- 

 rately, without luxating the lower jaw. It may not be 

 amifs to obferve that thefe luxations, depending on exceffive 

 loofenefs of the hgaments, are, by reafon of fuch loolenefs, 

 in general very eafily reduced. A dileafed llatc of joints 

 may alfo difpofe to luxations, by dcllroying the ligaments 

 and articular furfaces. What furgeon of any experience at 

 all has not frequently feen examples in which the head of the 

 thigh-bone has been diflocated, in confequence of difeafe in 

 the hip? Even the knee, which is a ginglimoidal joint, 

 fometimes becomes partially luxated in cafes of white- fwel- 

 hng. 



In order that external violence, a blow, a fall, or even 

 the aftion of the mufcles, produce luxation in a ball and 

 focket articulation, the axis of the bone muft be placed in a- 

 direction, more or lefs oblique, with refpeft to the furface 

 with which it is articulated. If, for example, the os humeri 

 hangs exadlly along the fide of the body, or perpendicu- 

 larly witli relpeft to the glenoid cavity of the fcapula,,Tlo 

 force can produce a luxation. If a perfon falls on the elbow,, 

 while the fore-arm is in this pofition, the head of the hu- 

 merus will be forced againll the cavity formed for its re-^ 

 ception ; but if the arm is lifted more or lefs from the body, 

 the axis of the humerus will fall obliquely on the furface of 

 the glenuid cavity, and-the efcape of-the head of the bona 

 from fuch cavity will be facilitated. This tendency to a 

 diflocation will be increafed in proportion as the angle 

 formed by the axis of the bone v.ith tlie furface of the gle- 

 noid cavity deviates from a right angle. In the gingli- 

 moidal articulations luxations may be caufed by a fall, cr 

 other kinds of external violence, and they are moltly incom- 

 plete. In the orbicular joints the adlion of the mufcles has 

 conflantly a fhare in the produftion of the accident. Thus, 

 for inftance, if a perfon falls on the elbow, wOiilll the arm is 

 raifed from the body, and carried direftly outvi-ards, the 

 Hiock which this part receives will certainly tend very much 

 to force the head of the humerus out of the glenoid cavity 

 on the lower a:id internal fide ; but the adlion of the pedorahs 

 major, latiffimus dorfi, and teres major, contributes alfo very 

 much to throw the bone out of its place. In fact the elbow, 

 relling on the ground, becomes the fulcrum, or centre of 

 motion of the humerus ; in this flate, we obey a mechanical 

 inllinft, which leads us fuddenly to bring the arm cljfe to 

 the body, and as the refiflance made by the ground prevents 

 this, the violent and inllantaneous contraftion of the pedto- 

 ralis major, latiffimus dorfi, and teres major, draws down- 

 wards aud inwards the head of the humerus ; the luxation 



being 



