For the most part this operation aims at straightening deformed limbs by division of the tendons where, as the result of sprain or other causes, they have become contracted, or where from congenital deficiency of development they are abnormally short. A preliminary dose of aloes or some diuretic medicine may be advantageously employed where the limb is thick or swollen, as this tends to remove any temporary swelling and bring the tendons more clearly into view.
Animals with contracted tendons have usually a very overgrown foot at the heel. This should be brought to the ordinary level before operation. The tendons which most frequently call for treatment are the large flexors of the fore and hind limbs, "per-forans" and "perforatus". Cunean tenotomy is practised for stringhalt when due to adhesions connected with spavin or other lesions in the immediate neighbour-hood, but is of doubtful value. The operation, in any case, should be performed under chloroform. The position chosen for dividing the "perforans" or "perforatus" tendon is a little below the middle of the canon, or rather less than half-way between the fetlock and knee of a fore-limb, and the fetlock and hock of a hind one.
The horse having been prepared, and everything in readiness, he is cast in the usual way, and the cross-straps are placed upon his legs above the hocks and knees (Plate LIV), the horse lying upon that side on which are the limbs we intend to operate upon, a position which will enable us to operate on the inner side of the limb. The writer's reasons for preferring the inner side are that the cicatrix is less in view than it would be if it existed on the outer side, and we are not likely to wound the oblique branch of nerve (fig. 502), which leaves the inner metacarpal nerve at the upper third of the space between the knee or hock, and fetlock, to join the outer at the lower third. If we are about to operate on the hind-leg, the upper cross-strap (Plate LIV) is buckled up tight, thus drawing the uppermost hind-leg as far forward as possible. The foot of the leg to be operated upon is now removed from the hobble: a web halter is placed around the leg above the hock, but below the cross-strap, its free end being held by two assistants, who are to pull, when desired to do so, in a backward direction. It will be seen that this traction will be directly against the cross-straps, which will fix the leg. A similar piece of rope is to be placed around the hoof; the heels of the shoe will prevent it from slipping off, and the free end is to be held by an efficient assistant, who also is to draw steadily when directed. To raise the leg a little it may be placed upon a cushion. The operator is now to place himself so as to be out of personal danger. The two men at the posterior rope are to draw firmly and steadily. The assistant at the foot rope is to flex the foot as the operator directs, who is now to grasp the tendons, which are quite lax, about midway between the hock and fetlock with his left hand, the fingers being placed beneath the tendons and the thumb above them (fig. 515). In this way we can to a slight extent separate one tendon from another, so as to feel distinctly the space between the two. (Varnell).
Fig. 512. - Cunean Tenotomy. Scalpel inserted, forceps holding away fascia.
Fig. 513. - Tenotomy. Tenotomy knife inserted beneath tendon. Skin cut away to show position of blade beneath tendon. Forceps holding sheath.
Fig. 514. - Tenotomy Knife.
After making a very small incision in the skin, the leg is slightly Hexed. The tenotomy knife (fig. 514) is then forced sideways between the tendons and the suspensory ligament. The point of the knife must not be allowed to puncture the skin on the opposite side of the limb, and when introduced it must be kept close to the tendons to avoid injury to the vessels and nerves running along their border. The blade is now turned so that the cutting edge is brought into contact with the part to be divided; the foot is then forcibly extended by an assistant acting on the foot rope, and by a firm, steady, sawing movement of the knife the tendon is severed. This will be made known by a sharp snapping noise emitted by the sudden parting of the divided portions. The operation being accomplished, the knife is withdrawn and the animal is allowed to rise. A piece of carbo-lized wool is now applied to the wound, and support given to the leg by the application of a linen bandage from the foot upward towards the hock or knee, as the case may be. In order to prevent any undue lengthening of the divided tendons during reparation a high-heeled or a patten shoe will require to be placed on the foot, and the animal must be supported by slings. At the expiration of a fortnight or three weeks the heel of the shoe must be lowered, and the position the foot takes on the ground carefully noted from day to day, so that should the heel show any signs of being drawn up as the tendon becomes reunited, a shoe with a long toe-piece or lever must be fitted to the foot in order to prevent undue contraction in the uniting substance.
It is customary with some to divide both perforans and perforatus, but in recent cases of contraction it suffices to divide the one or the other, whichever may need it. The complete straightening of the limb is not always immediately apparent, as in long-standing cases numerous adhesions may still prevent the heel from being brought to the ground, unless they are put upon the stretch and broken by forcible extension of the leg while the animal is under control. Where no such adhesions exist, the patient at once puts the heel down and the toe has a tendency to turn up.
Fig. 515. - Tenotomy of the Perforans Tendon, showing position of hands and knife.
After-treatment consists in keeping the wound aseptic by bandaging with suitable dressings (see Antiseptics Employed in the Treatment of Wounds) for a few days, during which it may be expected to heal. Tying up the animal's head to prevent interference with the limb is always desirable.
When the tendons have reunited and the new connecting material has become firm and dense, the horse may be turned into a soft meadow for two or three months until the parts have regained their original strength.
The application of a repetition of blisters to the leg will reduce any slight enlargement which may result from the operation, and if at the same time the patient be subjected to a course of iodide of potassium a still better result may be effected.
The success of the operation is generally greater in the fore than the hind limbs, but very much depends on the time which is allowed for repair. The posterior extremities having to bear the strain of propulsion in heavy draught, require that reparation be thoroughly completed before the horse resumes work, and for this reason a longer time should be allowed.
More or less thickening of the tendons always remains after the operation, but by keeping the wound thoroughly aseptic this will be very much under control.
The only operation of much practical value is that on the back tendons of the leg.