FIG. 3. Hinged splint applied in position of original deformity. Observe hooks carrying rubber bands, also wooden "plinth." The photograph was taken after straightening had been completed and it is only by voluntary contraction of the hamstring muscles that the leg is brought back to the position of original flexion. Observe that just above the malleoli a ring has been removed to relieve pressure on the dorsum of the foot and on the heel which developed in the process of straightening. A strip of adhesive plaster holds the cut ends of the cast together. Observe that in this flexed position the top of the cast fits loosely about the thigh.

with the hinge-pin away from the patella, upon the anterior surface of the "plaster cast." When adjusted as conveniently as possible to the leg and the thigh, the hinge will, ipso facto, lie in such a position that the hinge-pin will be in the plane bisecting the angle of deformity, and it will be found to occupy a position from I in. to 1/4 in. in advance of the patella. By tucking in fresh, wet plaster bandage beneath the edges of the hinge, and by buttressing it laterally with additional plaster bandage, the hinge should be evenly and securely bedded upon the anterior surface of the "plaster cast," and when the hinge is so bedded, the originally very light "cast" should be quite generously reinforced by turns of plaster bandage as far as the hinge reaches, i. e., 8 in. above, and as far below the knee, which turns should, of course, include and cover in the hinge and bind it down to, and practically incorporate it with the "plaster cast," as first applied.

To simplify our description let us suppose that the power we are to apply to effect our extension is the familiar one of wooden wedges opposite the popliteal space, as in the procedure ascribed to Lange. In that case, all that it is necessary to do to prepare the apparatus for "wedging" is to divide the "plaster cast" throughout its whole circumference in the plane bisecting the angle of deformity, thus converting the apparatus into two, contiguous "plaster casts," the upper "cast" extending from the perineum to the knee, and the lower from the knee to the toes, the two "casts" being joined together by the hinge in front of the patella.

If, indeed, we are to use "wedging" to obtain our extension, the apparatus is now complete, save for the introduction, opposite the popliteal space, of the wedges themselves. This, however, should be postponed for twenty-four hours or more after the application of the hinged splint, to allow the plaster of Paris to set and harden.

For the purpose of simplifying our description it has been convenient to choose wooden wedges opposite the popliteal space as the means of extending the flexed knee; in actual practice a much better means of extension is by rubber bands, conveniently

1⁄2 in. wide and 4 in. long, such as are used to hold bundles of letters or documents. For this purpose, some slight additions to the apparatus are convenient. The first of these is the secure fixation of a hook to the front of the cast, at a point about midway between the ankle-joint and the tibial tuberosity and of another hook at about the junction of the upper and middle thirds of the thigh. These two hooks should be so placed as to be just in line with the center of the hinge-pin.

A second addition is a wooden "plinth," a triangular prism, measuring on each side about 11⁄2 in., which may advantageously be used, like the bridge of a violin, to enhance the mechanical advantage of the action of the rubber bands.

The rubber bands can readily be slipped on or off the hooks, by the surgeon, by the nurse or by the patient himself, thus diminishing the amount of tension in a moment, in case it proves too burdensome, or increasing it, if not sufficiently efficacious.

Eight to ten rubber bands, 1⁄2 in. wide and 12 in. long (constructed by linking together three of the 4-in. stationer's bands), when stretched to 24 in., which may be taken as an average distance between the hooks in an adult, will exert a tractive force of from 48 to 60 lbs. A large, indeed, a very large proportion of this seemingly great tension is expended in inert strains and stresses on the apparatus, yet a certain proportion is exerted in extending the leg on the thigh. As long as the "plaster cast" and the iron hinge remain firm, we may ignore that element of our tractive force which is dissipated in strains and stresses within the apparatus, and we may add safely enough to our tension until we get the effect we seek, and we need not be frightened by calculations of 50-60-80 lbs. between our hooks.

We have already announced one paradox, namely, that by pulling down on the foot and leg in a line parallel to the axis of the trunk, we were actually forcing the tibia against the femur, instead of pulling them asunder. Behold now a greater paradox, in that by traction exerted from the femur upon the leg we tend to pull these two bones, not together, but asunder, and by this selfsame traction from thigh to leg we exert a thrust upon the foot and upon the pelvis, which demands the most

careful cushioning to make it bearable; and this thrusting pressure it is, and not the strain on the joint structures, intrinsic or extrinsic, pathological or normal, nor yet the contractured hamstrings, which sets a limit to the amount of power we can apply through our apparatus to the correction of a flexion deformity of the knee. In short, we have constructed that most powerful of mechanical appliances, a "toggle-joint"; and this, by virtue of that "nigger-in-the-woodpile," an eccentric fulcrum.

But let us now see if we cannot find some incidental advantages to be derived from the paradoxical antics of our eccentric fulcrum.

While it is desirable to remove all pressure, so far as possible, from the articulating surfaces of the knee-joint, and while it is even desirable to do more than this, and even exercise a positive distraction, or pulling apart of the joint surfaces, yet there is a limit to the amount of force which it is practicable to exert in this direction, though the amount of force we may apply with this apparatus, if need be, is limited only by the play of our "toggle-joint," and, as the sides of our strap-hinge, which is the thrusting element of our "toggle-joint," approach to 180 deg., the thrust increases, theoretically, to enormous proportions; practically, however, greatly limited by the yielding of the plaster of Paris structure, with which it is only more or less rigidly incorporated.

In cases where the distraction of the joint surfaces is deemed unnecessary, we can eliminate this element in the apparatus altogether by simply making the "plaster cast" shorter, so that it reaches neither to the perineum, above, nor to the ankle, below, but, as the flexion deformity is overcome, the "plaster cast," under the thrust of the opening angle of the strap-hinge, simply slides upward over the thigh, and downward, over the leg, without being long enough to impinge either on the pelvis or on the foot. Such use of the apparatus might be permissible in "rheumatic," or simply "toxic" cases, where the arthritis which provoked the flexion deformity may be supposed to have arisen. from a merely "chemical trauma." In cases, however, of actual bacterial invasion of the joint, such as an old suppurative arthritis,

or a "healed" tuberculosis of the knee, it will be the part of wisdom, in order to reduce to a minimum the changes of recrudescence of the arthritis, even at the cost of painful pressure elsewhere, to accomplish the correction of the flexion deformity of the knee with the safeguard of as much distraction of the joint surfaces as it is practicable to maintain during the straightening process. Available distraction the hinged splint affords in superabundant measure, and the only problem is to so arrange matters as to utilize this valuable safeguard to the utmost, without causing too much pressure on the foot and on the pelvis.

The first and most obvious means is to dispose moderately thick and elastic felt pads about the three points indicated above. It should be remembered, too, that the pressure can be instantly lessened, or released altogether, without other detriment than loss of time, by removing one or more, or, if need be, all of the rubber bands.

It is a matter of judgment to determine when it is best to reduce the element of distraction in favor of a larger element of pure opening out of the angle of flexion deformity; and it is always necessary to bear in mind that the very thrust against foot and pelvis, of which the patient will probably complain much more than of pain in the ankylosed knee or in the contractured hamstrings, is the very best safeguard and insurance against purchasing a straightened knee at the cost of a recrudescence of the arthritis. The surgeon will, therefore, at least in old septic and tubercular cases, not move too quickly to relieve pressure at the upper and lower ends of the "cast," save as he may be ready to ease it by casting off one or more of the rubber bands. The occurrence of actual pain in the knee, however, should be a signal for prompt lightening of the strain, or even for postponing the whole procedure.

If, however, the surgeon decides that the straightening cannot proceed further without lightening the pressure at the extremities of the apparatus, the way in which this should be accomplished is not by cutting away the plaster at the point of pressure, but rather by removing a complete ring of the "cast," about 1⁄2 in. wide, just above the malleoli, making the cuts even and true,