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1. The first skin incision, 2 inches long, bowed with the convexity toward the sole of the foot, is made over the insertion of the tibialis anticus.
2. Preparation of the Implantation Site for the Extensor Hallucis.—The tendon of the tibialis anticus at its insertion is slit longitudinally for about 1 inch, and the bone or cartilage
Fig. 104.—Semi-diagrammatic cross-section through the calf at the level of the upper pole of the extensor hallucis sheath. (From Biesalski and Mayer: “Physiological Method of Tendon Transplantation.”) Note that the tibialis anticus is separated from the extensor proprius hallucis and extensor longus digitorum by a strong fascial septum. of the internal cuneiform is grooved for the reception of the extensor tendon (see Fig. 103).
The implantation site is prepared before the extensor tendon is laid bare, so as to avoid exposing it to the air more than is absolutely necessary.
3. The Incision over the Extensor Proprius Hallucis Tendon. -This runs in the line of the tendon from a point 112 inches above the tip of the internal malleolus to the middle of the first
metatarsal bone. The reason for this long incision is evident, when the sheath of the tendon has been opened. Then it is seen that the mesotenon attaching the tendon to the floor of the sheath is too well developed to allow withdrawing the tendon from the sheath through a small supramalleolar incision.
It is well, however, not to expose the tendon unnecessarily at this stage of the operation, but to leave it in situ, until all has been made ready for transferring it into the sheath of the tibialis anticus.
Extensor proprius hallucis
Anterior tibal artery
Sheath of tibialis anticus
Sheath Tibialis posticus Flexor longus digi
Post. tibial artery Post. tibial nerve
Deep layer of fascia cruris
Fig. 105.-Semi-diagrammatic cross-section through the calf at the level of the upper pole of the tibialis anticus sheath 12 inch proximal to the preceding section. (From Biesalski and Mayer: “Physiological Method of Tendon Transplantation.”) Note that the three extensor muscles lie in the same fascial compartment.
4. This transfer requires an accurate knowledge of the fascial relations between the two tendons. Fig. 104, a diagrammatic cross-section through the calf at the level of the upper pole of the sheath of the extensor proprius hallucis, shows the extensor and the tibialis anticus divided from one another by a fascial septum derived from the fascia cruris. To run the extensor hallucis through this fascial septum would not be physiological. Fig. 105 at the level of the upper pole of the tibialis sheath, about 12 inch proximal to the preceding, shows the three anterior muscles of the calf lying within the same fascial compartment. This is the site of election. Here the operator can draw the extensor tendon into the sheath of the tibialis anticus, confident in the knowledge that serious postoperative adhesions will not result. Since this point lies slightly above the upper pole of the extensor hallucis sheath, the fascia over the extensor must be incised for 1 inch proximal to the sheath. The mesial fascial edge is
Fig. 106.—Clamp used to grasp the tip of the tendon during the operative manipulations. It enables the operator to hold the tendon firmly with a minimal degree of traumatization. (From Biesalski and Mayer: “Physiological Method of Tendon Transplantation.”)
grasped with the clamp shown in Fig. 106 and raised until the operator sees the anterior tibial tendon shimmering through the paratenon, which separates it from the extensor hallucis. Here a small incision is made directly into the tibialis sheath (Fig. 107). An eye-probe is passed through this incision in the line of the tibialis tendon, made to puncture the lower end of the sheath, and to appear over the insertion of the tendon.
5. The sheath of the extensor hallucis tendon is then slit open its entire length. The tendon is divided near the middle of the metatarsal bone, its end grasped with the tendon clamp (Fig. 106) and the mesotenon divided close to the tendon until the operator reaches the lowermost muscle-fibres. The vessels of the mesotenon are thus sacrificed, but a large vessel which runs through the lowermost muscle-fibres can always be spared. The tendon end is threaded with chromic catgut by the stitch shown in Fig. 108, the free ends of the suture are passed into the eye of the probe and the tendon thus readily drawn through the sheath of the tibialis anticus.
Withdrawing the tibialis anticus tendon from the sheath produces needless trauma and is unnecessary, since the sheath does not closely invest the tendon, but is large enough to accommodate two tendons.
Distal stump of extensor proprius hallucis
tibialis anticus The incised fascia
Lowermost muscle fibres of extensor proprius Mesotenon hallucis
Fig. 107.—Transplantation of the extensor proprius hallucis for the paralyzed tibialis anticus tendon. (From Biesalski and Mayer: “Physiological Method of Tendon Transplantation.") The implantation site over the insertion of the tibialis anticus has already been prepared (see Fig. 103). The extensor proprius hallucis has been exposed from a point slightly above the upper pole of its sheath almost to the head of the metatarsal bone. At the upper level of the incision a small opening has been made in the loose tissue (paratenon), which at this level (see Fig. 105) separates the extensor tendon from the tibialis anticus. Through this opening the extensor tendon is drawn downward by means of an eye probe which traverses the sheath and emerges over the insertion of the tibialis anticus tendon.
6. Fixation of the Tendon.—Here the knowledge of the law of tendon tension is important, since otherwise the operator is likely to sew the tendon under too great tension and thus throw an unnecessary burden on the transplanted muscle. It may be remembered that in outlining the physiology of tendons I showed that when the muscle is relaxed under narcosis and its origin and insertion are approximated, the tendon itself, as well as the muscle-fibres, have a zero tension (see p. 143 et seq.). Therefore, to give the transplanted tendon the exact physiological tension, one must merely approximate the origin of the muscle and its new point of insertion (in this instance, by holding the foot inverted and flexed dorsally), draw the tendon downward until it runs in a straight line, and suture it under just sufficient tension to maintain this desired course. With a
Fig. 108.—The fixation suture used in anchoring the transplanted tendon. (From Biesalski and Mayer: “Physiological Method of Tendon Transplantation.") I. A single transverse suture for small tendons. II. A double transverse suture for larger tendons.
little experience the operator knows beforehand just how long the tendon must be to reach its new point of insertion and the chromic gut suture, inserted to draw the tendon through the sheath, can thus be used as the fixation suture.
The implantation site has already been prepared (see second step of the operation) by slitting the tibialis tendon lengthwise and traumatizing the periosteum of the internal cuneiform. The tendon, threaded by the fixation suture shown in Fig. 108, is now fastened securely between the two halves of the tibialis tendon. The sutures are threaded on a stout cervix needle or an instrument resembling a shoemaker's awl, and are passed