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On the Use of Hinged Splints in the Treatment of

Certain Deformities and Fractures.

An Exposition of the Paradoxical Antics
of an Eccentric Fulcrum.

LEONARD W. BACON, M.D., New Haven.

Though in truth applicable to the treatment of a considerable variety of lesions, including both actual deformities and the potential deformities incident to many fractures, the principles of the "hinged splint" are exhibited, in perhaps the simplest and clearest manner, in its application to the gradual correction of fibrous flexion-ankylosis of the knee, which use of the apparatus may therefore serve us conveniently as a paradigm.

Two methods of combating this deformity are in common use, first, traction upon the foot and lower leg by weights, and, secondly, the "wedging" of a partly divided plaster cast, according to the method ascribed to Professor Lange, of Munich.

Let us consider then first the straightening of the flexed and ankylotic knee by means of weight extension, and let us analyze the mechanics of the operation. Let us, however, premise the statement that most cases of fixation of the flexed knee are the result of an arthritis of the knee-joint, that efforts at straightening want to be begun as soon after the subsidence of the arthritis as possible, yet that it is necessary to guard very carefully against a reëxcitement of the arthritis through any "insult" to the articulating surfaces of the adjacent bones by forcibly pressing them together.

It would appear at the first glance that all the indications, save that of effective mechanical advantage, were met by traction on the foot and lower leg. Traction is made substantially parallel to the axis of the trunk, and it would seem that the joint surfaces would be virtually, if not actually pulled asunder and not jammed together by the traction distal to the knee. But

closer scrutiny shows that this view is fallacious, and that in fact heavy compression of the joint surfaces occurs, a compression that is many fold greater than the tractive force below.

This paradox is readily elucidated by study of the mechanics of the problem.

In the flexed knee with contractured hamstrings we have virtually a tongs. As the patient lies on his back, with heel and buttock resting on the bed or table, the hinge of the tongs may be considered to lie in the tendons of the contractured hamstrings, along a line behind the joint, substantially in the plane of the articulating surface of the tibia.

A,,B

Y

N

If, in the diagram above, X represents this hinge-point, then Y-X may represent the lower leg and foot, as one handle of the tongs, and Z-X will represent the thigh and pelvis, as the other handle of the tongs. The jaws of the tongs will then be represented by the articular surfaces of the tibia and of the femur, indicated by the lines A-X and B-S respectively.

Now it is evident that the separation of the handles, Y-X and Z-X, of the tongs is going to result in pressing together the jaws, A-X and B-X, of the tongs; and it is likewise evident that the mutual compression of the opposed surfaces of the jaws will bear the same proportion to the force separating Y from Z that the length of the handle Y-X bears to the length of the jaw, A-X; and that, in view of the relation between the length of the leg, Y-X, as one element (the handle of the tongs) and the antero-posterior diameter of the knee as the other element (the jaws of the tongs), this mutual compression of the articulating

surfaces is many fold greater than the force applied to draw Y and Z apart, so as to bring them into a straight line with the hinge, X.

In actual practice, the effect of this joint-surface compression in revivifying a recent arthritis has proved so active that the attempt to straighten the flexed joint by traction has had to be, in many cases, either abandoned or postponed.

To mitigate these untoward effects the method of "wedging" was introduced. In this method the limb is encased in plaster of Paris and the plaster shell is cut through, in the line of the articulation, for about three-quarters of its circumference. Opposite the popliteal space a thin wooden wedge (in practice, most conveniently a "throat-stick" or wooden "tongue-depressor") is introduced into the cut made in the plaster, and daily an additional wedge is inserted until a sufficient thickness of wedges has been placed to widen the gap opposite the popliteal space to such an extent as to force the leg and thigh into full extension.

Two practical inconveniences have been found to attend this method of extension. First, the operation is found to develop a considerable amount of pressure on the skin over the patella, causing pain, and only imperfectly obviated by the interposition of a thick cushion of felt over the knee. Secondly, where the angle of the deformity is considerable, the uncut plaster in the region of the patella crumbles, after a certain number of wedges have been inserted, and the cast has to be removed and reapplied to complete the extension. Moreover, the mutual compression of the joint surfaces, though mitigated, is not overcome, and to the compression between the tibial and femoral articular surfaces is superadded a very decided, and most undesirable compression between the articulating surfaces of the patella and the femur, often the occasion of pain, and prone to result in recrudescence of the arthritis. The wedging process represents, however, a distinct advance over the method of extension by traction, in that the fulcrum about which the levers swing is moved from below, or rather behind the knee, in the plane of the hamstrings, to a plane much nearer that of the patella.

The true mechanical principle to employ in the extension by leverage of a flexion-ankylosis is to bring the fulcrum upon which the levers are to swing beyond the apex of the deformity, so as to combine with the extension the element of distraction. To accord with this general principle of sound surgical procedure, in the case of the knee-joint, the fulcrum should be in front of the patella, not behind it, as is virtually the case when extension is made by traction on the lower leg, nor at about the plane of the patella, as in the ordinary method of "wedging."

This principle is squarely met, but is rather cumbrously and awkwardly carried out by Turner's "irons." A much simpler and handier method is by the use of a hinged splint, as devised by the writer, which apparatus carries with it many incidental advantages and possibilities which it is the object of this paper to indicate.

The application of the apparatus is extremely simple. As the first step the limb is encased in "stockinette," over which is laid a few thicknesses of "sheet-wadding," most conveniently applied in the form of loosely rolled bandages. As no pressure at all will be exerted over the patella, it is unnecessary to provide a special felt "knee-pad," as in the wedging process. On the other hand, if we are to obtain the full benefits of the "distraction," or pulling asunder of the joint surfaces, which the apparatus is capable of affording, it will be well to place moderately heavy felt cushions in three places where increasing pressure must come with the progress of the extension, to wit, over the front of the ankle-joint and the dorsum of the foot; over the tendo Achillis and the protuberance of the heel; and over the tuberosity of the ischium and along the femoro-perineal fold.

Over the leg thus swathed and provided with pads at the points indicated is then applied, as a second step, a light plaster of Paris casing, which should extend downward, to include the foot, as far as the toes, and upward, as far as the perineum and the groin.

As soon as the limb is encased in the plaster of Paris, an 8-in. malleable iron strap-hinge, such as can be purchased for a few cents in any hardware store, is laid "wrong side out," i. e.,

[graphic]

FIG. 2. X-ray of hinged splint applied to anchylotic knee with cast divided in a line bisecting the angle of deformity. Observe that the fulcrum, i. e., the hingepin, lies at least 11⁄2 in. above the patella and also the space beneath the hinge-pin where the plaster has been entirely cut away. Obviously no patellar pressure can occur. Observe also that the line of division of the "plaster-cast" comes not opposite the articulating surface of tibia and femur but passes through the axis of rotation of the knee-joint which lies an inch or more nearer the pelvis.

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