5. The upper articulation of the humerus, though predisposed, in
general, to luxations, is not equally so in every direction. There
is a point at which luxation cannot take place. There are others,
where, though possible, this accident has never been observed. It is
necessary, therefore, before examining the mechanism of this luxation,
to mention with precision, the directions in which it may occur.
On this point, writers have differed in a very singular manner.
Sometimes, to express the same thing, they have used a different
language; and, at other times, have, by the same words, expressed
things widely different. Always agreeing as to certain modes of
dislocation, they have been divided as to others; while, in the midst
of those contrarieties, the surgeon being embarrassed, is at a loss on
what ground to found his practice.
6. The ancients, knowing but little of the natural relation of
the parts surrounding the joint, were ignorant of the accidental
ones, which these several parts assume, in the case now under our
consideration. Hence, without doubt, arises the confusion, of their
opinions on the subject.
Many admitted of four kinds of luxations; a great number acknowledged
only three; some subscribed to but two; while others believed in the
possibility of none but one.
7. The first divided differently the directions in which the bone might
be luxated. Some contended for luxations upward, downward, forward,
and backward; and such was the opinion of the first Greek physicians,
predecessors to the father of medicine, who has transmitted the opinion
to us accompanied with a demonstration of its fallacy. Others have
divided them into those that take place downward, upward, outward, and
forward. This division is adopted by Galen, who yet produces only an
example of a forward luxation, and does not give us to understand what
he means by a luxation upward and inward.
8. The second distinguished the modes of this luxation, sometimes
into downward, forward, and backward; as was the case with Oribazes;
at other times, into downward, outward, and inward, according to the
opinion of Paul of Egina, who, no doubt, adopted exactly the preceding
division, expressing it only in different words; sometimes into
downward, forward, and upward; such was the sentiment of Albucasis,
who, notwithstanding, considered a luxation upward, as a very
difficult, and very rare occurrence.
9. The third were of opinion, that, in undergoing a displacement, the
head of the humerus could be carried only downward, under the arm-pit,
which is the most common direction, or forward, a course which it takes
more rarely. Celsus is almost the only writer who has contended for
this division. “_Humerus_, says he, _modo in alam excidit, modo in
partem priorem_.”
10. Lastly, The fourth believe, with Hippocrates, in none but a
displacement downwards, the only one which that physician has met with
in his practice. “_At vero humerus, inferiorem in partem excidit; aliam
in partem excidere non audivi._”
11. The moderns, in borrowing from the ancients their divisions of
luxations, did not, like them, determine a priori and in a vague
manner, the precise spot and direction of displacement; but ascertained
these points by subsequent observation, with more precision, in
proportion as a knowledge of anatomy shed light on them. They also paid
particular attention to the essential difference between primitive and
consecutive luxations.
12. Petit admitted of four kinds of luxations, 1st, downward, on
the edge of the scapula: this is a very rare occurrence: 2dly,
outward, under the spine of that bone, a kind very difficult to be
primitively produced. 3dly, inwards, under the hollow of the armpit.
4thly, forward, between the corocoid apophysis and the clavicle. With
this illustrious practitioner, Heister acknowledged four kinds of
displacements; but, here again, was a new variety, both in expression,
and in meaning. The one says, downward, under the arm-pit, the other
forward, under the pectoralis major; the one, backward, under the
scapula, the other outward, under its spine. According to Duverney,
luxations are never primitively in any other direction than downward;
the others being only the subsequent effect of muscular action.
13. In the midst of these very complicated modes of treating a very
simple subject, it is necessary, first, in order to acquire definite
ideas, to divide luxations of the humerus into primitive, which are the
immediate effect of external violence, and consecutive, which succeed
the primitive, through the influence of causes which I am about to
consider.
Let us suppose four lines to inscribe, in form of a parallelogram, the
oval surface of the glenoid cavity, one representing the superior edge,
another the inferior, a third the internal, and the fourth the external.
14. It is evident that the head of the humerus cannot be displaced
towards the superior edge. In that direction, must be encountered, the
acromion and corocoid apophyses, the strong ligament passing between
them, the tendons of the triceps and supra-spinatus muscles, and the
fleshy mass of the deltoid; all which, taken together, constitute an
insurmountable obstacle to the escape of the head of the bone upwards.
Besides, what power could carry it upwards? In order that this kind of
luxation might take place, it would be necessary, that the head of the
bone should be carried outwards at the same time, as well as upwards,
a circumstance which is impossible, because the trunk prevents the
lower extremity (the elbow) from being directed sufficiently inward to
produce such an effect.
15. On the contrary, in other directions, but very little resistance
is to be met with. Towards the inferior edge of the cavity, the long
portion of the triceps; the tendon of the subscapularis, towards the
internal edge; and towards the external edge, the tendons of the
infra-spinatus, and teres minor, yield with ease to a force directed
against them, and permit the occurrence of primitive luxations,
downward, inward, and outward. Downward, between the tendon of the
long portion of the triceps, and that of the subscapularis; inward,
between the subscapulary muscle and fossa;[14] and outward, between the
fossa infra-spinatus and the muscle of the same name. These modes of
displacement are not alike frequent, as will be mentioned presently.
[14] (_La fosse sous-scapulaire_). I know of no English anatomical
term for this. I therefore translate it literally. The same is true
with respect to “_fossa sous-epineuse_,” translated here, fossa
infra-spinata. TRANS.
16. Having escaped from its cavity, and being primitively placed in
one of these three situations, the head of the humerus oftentimes
changes its position. Then, to a primitive luxation downward or inward,
succeeds a consecutive or secondary one; but never to a luxation in an
outward direction, if such ever occur, because the spine of the scapula
forms an obstacle to it.
A secondary luxation inward, may succeed a primitive one downward;
there is nothing to oppose the head of the humerus in the course it
takes, to enter between the subscapulary muscle and fossa. If, on the
other hand, it be disposed to pass to the external side, the tendon of
the triceps opposes it; and, notwithstanding what Petit has advanced,
there is no secondary luxation in that direction.
17. It sometimes happens, that, having escaped either from the internal
part, or from the inferior part of the capsule, the head passes behind
the clavicle, and forms there a secondary luxation upwards, as has
been observed by Ambrose Pare, and by Gallien, and of which an example
or specimen was preserved in the cabinet of Desault. But, here, the
secondary displacement must take place in a slow manner, and when it
has taken place, art can seldom remove it, on account of the strong
adhesions formed by the bony surfaces. Thus, in the example mentioned,
there was a new cavity formed behind the clavicle, and the humerus
adhered to the surrounding parts by a kind of new ligaments.
18. It appears from what has been said, that the humerus is subject to
four different kinds of displacement. 1st, _Downward_: 2dly, _outward_,
in both of which directions the luxation is always primitive; 3dly,
_inwards_, where it is sometimes primitive, and sometimes consecutive;
4thly, _upwards_, where it can never be otherwise than consecutive.
The second and fourth are very rare occurrences, and bear so small a
proportion to the others, that the latter alone ought to command the
attention of the practitioner.
§ III.