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branches cut longitudinally. The tendons are most vascular near the insertion of the mesotenon; that is, near the hilus. Here the numerous branches of the mesotenon ramify in the epitenon and send numerous fine twigs into the tendon.

Friction surface of tendon
Fascial layer of sheath

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Fold of con

Endotenon nective tissue

Epitenon Fig. 101.—Microscopical cross-section through the flexor longus hallucis tendon of an infant eight months old, to illustrate the situation of the blood vessels of the tendon. Note that the largest vessels run in the connective tissue on the deep surface of the tendon (epitenon) and that smaller vessels are present in the connective tissue speta (endotenon) between the tendon bundles. Near the gliding surface of the tendon no blood vessels are present, since this corresponds closely in structure and in function to the cartilage of the joint. The nuclei of the tendon cells near the gliding surface, instead of showing the usual elongated form, are round and closely resemble those of fibro-cartilage.

The Tension of Tendons.-For many years, orthopædic surgeons have been engaged in controversy as to the proper tension under which transplanted tendons should be sutured, one maintaining that the tendon should be sutured under the greatest possible tension, another claiming that the tension should be "moderate," and still a third, that there should be no tension. The solution depends upon a satisfactory answer to the question: What is the normal tension of a tendon? To answer this physiological problem which, for some reason or

other had never engaged the attention of physiologists or anatomists, I performed the following simple experiment. Under anæsthesia, the tendon of a dog was divided near the point of insertion, and to the proximal stump, which retracted one or more inches, owing to the pull of the muscle, a stout silk suture was attached and fixed to a spring scale.

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Fig. 102.—The spring balance used to test the tension of tendons. By shifting the position of the handle and the silk suture, readings can be taken from 25 grammes up to 10 kilogrammes.

By traction on the handle of this scale (see Fig. 102) the tendon stump could be pulled downward until it was brought in contact with the distal stump, and by means of the scale an exact reading could be made of the number of pounds' pull required to bring the tendon ends into apposition. This represented the traction to which the tendon was subjected by the muscle, since the operator had to exert just this much pull to overcome the muscular resistance. By varying the conditions of the experiment, using larger and smaller muscles, light or superficial anæsthesia, resting muscle or muscles stimulated electrically, a great number of data were secured bearing upon the question of tendon tension. Despite the great range in the degree of tension to which the tendon is subject, one fact remained constant in all the twenty animals tested experimentally and in the observations during operations on human beings: when, under anesthesia, the origin of an inactive muscle and its point of insertion are approximated to the physiological limit, that is, when the limb is passively held in the position which the active contraction of the muscle would cause it to assume, there is no tension on the tendon.

The practical application of this law is simple. To restore the normal tension the operator need only approximate origin and insertion of the muscle and tendon in question and suture the tendon to its new position without any tension whatever. For instance, in transplanting the peroneal tendon for the paralyzed tibialis anticus, the foot should be held in the position of calcaneovarus and the peroneal tendon sutured to its new point of insertion with just sufficient tension to render it taut.

General Principles of Tendon Operations.—On the basis of these and numerous other anatomical and physiological data, a system of operations has been worked out whose basic principle is the correlation of every step of the transplantation with the normal mechanics of tendon motion. The surgeon must take cognizance not only of the course and insertion of the tendon as given in the anatomical textbooks, but of many other less known but equally important facts, such as the blood supply of the tendon, its fascial relations at various levels, its length, range of motion, its action, not merely in the normal situation, but when the point of insertion has been altered, the exact location and inner architecture of its sheath, the character and line of insertion of the mesotenon, and the bursæ associated with the tendon.

A physiological tendon operation must conform not only with the general surgical principles of absolute asepsis, minimal hæmorrhage and minimal traumatism, but also with the following demands:

1. It must whenever possible restore the normal relationship between the tendon and the sheath.

2. The course of the tendon from its original site to that of the paralyzed tendon must run through tissue adapted to the gliding of the tendon. Injury to the periosteum or the crude boring of a hole through fascia or interosseous membrane is inconsistent with this demand.

3. The normal insertion of the tendon must be imitated wherever possible by implanting the tendon directly into bone or cartilage, preferably at the insertion of the paralyzed tendon.

4. The normal tension of the transplanted tendon must be reëstablished and the physiological length of the transplanted muscle thus maintained.

5. The line of traction of the transplanted tendon must be such as to enable it effectively to do the work of the paralyzed tendon.

Although the chief field for the application of these operations is in the treatment of the residual paralyses of anterior poliomyelitis, they are also applicable to those paralyses resulting from gunshot injuries which are not amenable to nerve suture or neurolysis. Thus, a lesion of the anterior tibial nerve just after it has branched from the parent trunk can seldom, if ever, be cured by operation on the nerve, since the numerous fine muscular branches, given off at this level, cannot be found in the scar tissue. So, too, a lesion of the posterior interosseous nerve does not lend itself to direct operative treatment. Under these conditions tendon transplantations are indicated.

I shall not attempt describing all the transplantations which can be considered physiological, but only some of those which in my experience are available in the treatment of gunshot injuries.

Transplantation of the Extensor Proprius Hallucis for the Paralyzed Tibialis Anticus. I have only twice had occasion to perform this operation, since it seldom occurs that a projectile produces an isolated injury of the nerves to the tibialis anticus. When, however, there is an isolated paralysis of this muscle, the following transplantation is an excellent method of relieving the tendency to valgus deformity.

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Paralyzed

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III Fig. 103.—Method of anchoring the transplanted tendon. (From Biesalski and Mayer.) I. The paralyzed tendon is slit longitudinally at its insertion and the surface of the bone and periosteum are scarified to stimulate osteogenesis. II. The transplanted tendon, sutured by the stitch shown in Fig. 108, is firmly anchored between the halves of the split paralyzed tendon. The needle passes through cartilage or bone, ligament and muscles so as to get a mechanically firm grip. III. The halves of the split tendon are united over the transplanted tendon by a series of fine sutures, thus bringing the transplanted tendon into intimate contact with the traumatized bone. During the normal ng process, firm fixation occurs by the sixteenth da

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