11. To form an idea of the signs or appearances of a luxation
backwards, let us examine, for a moment, the natural situation of the
olecranon, and the condyls of the humerus. As these eminences are
easily felt under the skin, a knowledge and recollection of their
situation will serve as a standard of comparison, to judge of the
changes they experience in a luxation. When the fore-arm is extended,
the olecranon is on a level with the internal condyl, and a little
above the external one. In a state of flexion, it descends below this
level, and is then farther below the internal than the external condyl.
In either situation, it is nearer to the first than to the second, the
radius separating it from the latter.
12. But, when a luxation has taken place, this apophysis, still
remaining on a level with the two condyls, even although the fore-arm
be half-bent, is oftentimes separated from the internal one, and driven
towards the other: a preternatural protuberance announces this change
of position of the olecranon. The coronoid apophysis, whose posterior
surface glides in the large groove of the humerus, corresponds to this
groove now only with its anterior surface: sometimes the olecranon
cavity[21] receives its extremity. The radius passes backward over
the small head of the humerus. At the fold of the arm, a transverse
protuberance, more perceptible on the internal side, announces the
presence of the displaced articular extremity of the os humeri. Over
this extremity are reflected the biceps and the brachialis muscles
in a state of violent distension. These muscles, greatly irritated
by such distension, continue in a state of habitual contraction, in
consequence of which, they keep the fore-arm half-bent. Nor can the
anconeus muscle, which is necessarily relaxed, act so as to prevent
this semiflection. Severe pains would be the consequence of attempts to
extend the fore-arm; the limb is in a state of pronation; yet I find
among the cases collected by Desault, several examples where supination
existed; this state is explained by the relaxed condition of the
pronator muscles. At the level of or opposite to the coronoid cavity
is a depression or hollow manifesting the absence of the apophysis of
that name.
[21] That deep depression in the os humeri, which, in a natural
state of the parts, receives the upper end of the olecranon process.
TRANS.
13. Should chance give rise to a luxation forward, an anterior
projection of the two bones of the forearm, and above all, of the
coronoid eminence, a depression corresponding to the olecranon
cavity, the extremity of the humerus carried backward and downward,
the rigid extension of the fore-arm, a protuberance behind formed by
the fractured olecranon (5), and severe pains, necessarily resulting
from attempts to bend the limb, &c. would constitute the principal
characteristic signs of the displacement.
14. In lateral luxations, a protuberance at the internal or external
side of the articulation, always shows of what kind it is. If the
displacement be to the internal side, the olecranon is then situated
behind the small tuberosity: the middle protuberance of the os humeri
bears on the radius, which is sometimes placed even behind the internal
articular eminence of that bone, which then rests on the external
depression of the great sigmoid cavity. Hence, as Petit judiciously
observes, arises the direction of the fore-arm outward, the above
eminence presenting a manifest obliquity in that direction. In this
luxation, the ulna has been known to lose entirely its connexion
with the humerus, and the radius to be brought into contact with the
internal condyl of that bone. This is what some authors call a complete
luxation. Others reserve that name for cases where, the two articular
ranges have lost their correspondence or apposition entirely.
15. In a luxation outwards, the olecranon corresponds to the external
condyl; the middle projection of the humerus, to the internal
depression of the great sigmoid cavity; the small head of this bone, to
the external depression; the radius projects outwards; and the humerus
makes a protuberance inwardly.
16. After all, these changes of situation vary remarkably, and it
belongs to theory rather than practice, to trace their history, with
precision. In general, luxations outwardly happen more frequently
than those inwardly, a circumstance which is fully explained by the
structure of the joint. In both, the lateral ligaments are almost
always lacerated.
A swelling more or less considerable accompanies all the different
kinds of luxation, and is sometimes carried so far as to involve the
diagnosis in great uncertainty, particularly when the displacement is
not very great. This phenomenon (the swelling), seems, in general, to
correspond, in a direct ratio, to the force with which the articulation
resists. Indeed the violence, and consequently the irritation, are
always in proportion to the resistance of the parts.
§ IV.