One of the most remarkable of the external signs of this injury is an increase of breadth of the fore-arm in the line of the articulation. There is a considerable projection seen at the outer side of the arm formed by the head of the radius, and an angular depression immediately above this. On the inner side of the arm we see the prominence formed by the inner condyle of the humerus, and its lower extremity. The fore-arm is flexed, and the patient feels it impossible to move the joint. The deviation and curved direc tion outwards given to the biceps and triceps, and approximation of the olecranon to the outer condyle of the humerus, all taken toge ther sufficiently characterize this rare accident.
In the incomplete luxation inwards, the cavity of the superior extremity of the radius, in abandoning the small head of the humerus, may be carried more or less inwards, and be placed under the internal border of the articu lar pulley or trochlea of this bone, while the inner edge of the great sigmoid cavity of the ulna and olecranon process must project in wards beneath the inner condyle of the humerus. The ligaments must be all torn as well as some of the muscles arising from the internal con dyle of the humerus, the biceps and triceps are turned from their usual direction and are curved inwards, and the ulnar nerve must be more or less stretched. The external signs of incomplete luxation inwards are what the anatomy of the parts above described would lead us to expect; there is a remarkable increase of breadth across the line of the joint, perma nent flexion of the fore-arm, and a powerless condition of the limb, all which were noticed in the former case. \Ve must add to these u remarkable projection below and internal to the inner condyle of the humerus, formed by the internal edge of the great sigmoid cavity of the ulna. Our attention is also attracted by the approximation of the olecranon process and inner condyle of the humerus to each other, and the distance of the olecranon from the outer condyle of the humerus, which forms a remarkable projection externally.
3. Under the head of lateral luxations of the elbow-joint, Sir A. Cooper has described accidents which might perhaps be more cor rectly designated—a, complete luxation of the bones of the fore-arm at the elbow backwards and outwards ; b, complete luxation of the bones of the fore-arm at the elbow backwards and inwards.
a. Luxation of the bones of the forearm backwards and outwards.—In this case the uloa, instead of being thrown into the posterior fossa of the os humeri, has its coronoid process situated on the back part of the external con dyle of the humerus. The projection of the ulna backwards is greater in this than in the former luxation, and the radius forms a pro tuberance behind and on the outer side of the os humeri, so as to produce a depression above it. The rotation of the head of the radius can be distinctly felt by rolling the hand.
b. Luxation of the bones of the fore-arm backwards and inwards.—Sometimes the ulna is thrown on the internal condyle of the os humeri, but it still projects posteriorly, as in the external dislocation, and then the head of the radius is placed in the posterior fossa of the humerus. The external condyle of the humerus in this case projects very much out wards, and the usual prominence of the inter nal condyle is lost. The olecranon process approaches nearer than natural to the middle line of the body, and is pointed inwards, being thrown more posteriorly than in any other lux ation.
4. Luxation of the ulna alone directly back wards.—The ulna is sometimes thrown back upon the os humeri, without being followed by the radius. The appearance of the limb is much deformed by the contortion inwards of the fore-arm and hand ; the olecranon projects, and can be felt behind the os humeri. Exten sion of the arm is impracticable but by force, which will reduce the luxation, and it cannot be bent to more than a right angle. It is an accident somewhat difficult to detect, but its distinguishing marks are the projection of the ulna, and the twist of the fore-arm inwards. A specimen of this accident is preserved in the Museum of St. Thomas's Ilospital ; the luxa tion had existed for a length of time. The coronoid process of the ulna was thrown into the posterior fossa of the humerus, and the olecranon was found projecting behind the humerus much beyond its usual situation. The radius rested upon the external condyle, and had formed a small socket for its bead, in which it was able to roll.* The coronary and oblique ligaments had been torn through, and also a small part of the interosseous ligament. The brachialis antieus was stretched round the trochlea of the humerus, and the triceps had been carried backwards with the olecranon.