The primary function of tendons is to transmit the energy of muscular contraction to the bony skeleton to create movement, an action that should be accomplished with as little loss of force as possible. All tendons have the basic physical characteristics of high tensile strength, compactness, and a smooth surface; however, they can very in thickness, length, and shape. In order to move over the joints that they span, they must not be inhibited in their longitudinal movement. This movement is assisted by the smooth surrounding tissues that act as gliding pathways.
In animals the most frequently injured tendons are located in the lower portions of the limbs and include the superficial and deep flexors and extensors of the forepaw and not infrequently the common calcanean (Achilles). Most of these injuries, particularly to the flexor tendons, are caused by lacerations by sharp objects, whereas the extensor tendons appear to be more prone to mechanical injury. The calcanean tendon is most frequently severed as a result of fights or car injuries or is ruptured by extreme flexion of the hock. Other conditions that are observed in animals are contracted tendons or abnormally long tendons. As a general rule these conditions are limited to the flexor tendon; however, not in all cases. Loss of function of any tendon can occur as a result of binding scars or atrophic contracture of its corresponding muscle.
Tendon surgery is far more complicated than is generally recognized. It requires a detailed knowledge of anatomy and fundamental concept of tendon function. In addition, the basic pathologic changes that can and do occur must be understood. The type and degree of trauma have great bearing on the method and timing of repair. One of the reasons for the complicated nature of tendon repair is the fact that the surgeon is dealing with a type of specialized wound healing in which he desires healing to occur at the ends of the anastomosed tendons but desires no healing to occur between the tendons and the surrounding tissues. Yet all of these structures are in the same wound. Repair of tendons that have a small amplitude of movement, such as most extensor tendons, or tendons that move in conjunction with other tendons does not offer the same challenge as does surgery of tendons that change direction within a restricted area and are surrounded by immovable objects, such as bone. Most frequently in the latter circumstance one is dealing with the development of a single scar that may inhibit tendon movement. This scar may be desirable for the healing of the tendon but can be a disaster as far as restoration of function. The inability to understand completely the series of events that occurs during tendon healing has led to the development of empirical manipulations that appear to create strong anastomosis of the tendon and adequate function. Along with the development of the empirical technical maneuvers, a greater understanding of primary connective tissue biology has developed, giving us a better insight into the reason that some of the techniques have improved the results of tendon repair whereas others have not. With a more fundamental understanding of the processes by which healing takes place both biochemically and biophysically, surgeons in the future will be less dependent than they are at the present time on exacting surgical techniques. Proper postoperative management and meticulous surgical technique are important in ensuring good results.
The reader is referred to chapter 4 for a detailed description of tendon healing. A discussion of tendon healing can also be found in articles by Peacock(12) and Lipscomb.(9)
General anesthesia is indicated for the surgical repair of most tendon injuries and abnormalities in animals. The importance of hemostasis during the surgical procedure cannot be overemphasized. The surgical procedure itself must ensure as little injury to the tendon and surrounding tissue as possible. Excessive bleeding leads to unintentional trauma of the tendon and these tissues. The best example of this is excessive sponging, which irritates the tissues. Hemostasis can be accomplished by the use of properly applied tourniquets and the judicious use of electrocoagulation. Ligatures must be applied only if absolutely essential to prevent arterial bleeding.
At one time it was thought that incisions should be longitudinal to provide better exposure over a longer area of tendon; however, this tends to create a longer area of scar tissue and an increased possibility of long binding scars that inhibit function. Therefore, an incision should be transverse to the longitudinal axis of the tendon if it is feasible to perform the surgery with that limited exposure. If not, the primary incision should be made parallel to the tendon at some distance through the skin and then perpendicular through any underlying soft tissues. Damage to the surrounding tissues that make up the so-called gliding mechanism must be avoided.
At no time should the tendon or the surrounding tissues be allowed to dry. Therefore, saline and suction should be used to adequately visualize the field if minor bleeding occurs. At no time should the tendon be grasped with forceps or wrapped in gauze. The only place that a tendon should be handled with forceps is in an area that will either be removed or where the creation of an adhesion is desirable.
The tendons can be repaired either primarily or secondarily. The history of the original wound is important, as is the degree of trauma to the tendon and its surrounding structures. It is unwise to attempt primary repair of a severed tendon that overlies a fracture because the tendon repair can become incorporated into the callus of the healing bone and render the musculotendinous mechanism nonfunctional. One must keep in mind the one wound-one scar concept. The same principle holds true if the wound has been grossly contaminated or infected. A rule of thumb that one can follow is that primary tendon repair can be attempted during the "golden period" (4 hours following injury) providing none of the above-mentioned problems are presents This period may be extended a little if the wound is perfectly debrided; however, extensive contusions resulting in lower tissue vitality contraindicate the use of primary repair. If possible, the surgical procedure should be planned in advance to reduce the surgical time. Under all circumstances asepsis must be maintained because infection will result in binding adhesions. If too much time has elapsed or gross contamination has occurred, the area can be debrided and a small piece of colored suture material placed in each end of the severed tendon. This will facilitate location of the tendon ends during a secondary surgical repair after the wound has healed and there is no longer any evidence of infection.
Occasionally at the time of injury one of the tendon stumps (the proximal end) will have retracted. Rather than searching for the stump in the original wound and lengthening the opening of the tissue surrounding the tendon, it is wise to make a small transverse incision proximal to the site of injury and locate the proximal stump of the tendon; thus you have the original wound and a small incision proximal to it. A small blunt probe can then be inserted through this incision beside the proximal stump of the tendon and gently pushed into the area of the original wound, marking the tendinous pathway. The tendon stump then can be withdrawn from the original area of injury, thus threading the tendon through its original pathway, and anastomosis of the severed end of the tendon is accomplished.
The ideal tendon suture should have high tensile strength, should tie in such a way that extra knots are not required, and should not create reaction within the tissue. The pattern should be simple and not tend to strangulate tissues; it should contain a minimum of suture material.(10) No one suture pattern is Satisfactory for all tendons; therefore, a variety of patterns are employed and the choice of pattern is based on the anatomical configuration of the tendon. Round or semiround tendons can accept the use of a Bunnell-Meyer(3) suture pattern, whereas flat tendons do not lend themselves to this technique; in the latter, an overlapping suture pattern may be preferable. When applying the Bunnell-Meyer pattern, the end of the divided tendon can be grasped with a tissue forceps on the very end to facilitate placement of the suture. The forceps is held between the thumb and middle finger, allowing the tendon to rest against the index finger (Fig. 68-1). A double-armed suture with a straight needle at each end is preferable; either nylon or stainless steel can be used. My preference is stainless steel because it provokes less tissue reaction. The first stitch is placed approximately 11/2 cm from the end of the tendon. The needle should pierce the tendon transversely and then reenter at an angle of about 45° pointing toward the cut end. The second stitch is placed at right angles to the first (Fig. 68-2). Two crisscrosses are generally sufficient. The traumatized portion of the end of the tendon can be removed with a sharp scalpel or a razor blade, exposing a fresh cross section of normal tendon. When this has been completed, the tendon is steadied and the needle is again inserted at a 45° angle and brought out in the middle of the tendon's cross section. This procedure is followed with a second needle, resulting in a double crisscross stitch that leaves only a small amount of suture material on the surface of the tendon with both ends of the suture coming through the end of the cross section. With proper application, little or no suture material will show on the tendon surface. The needles are then placed into the distal stump near the center at diverging 45° angles and a similar pattern is placed in the distal stump. If stainless steel (34- or 35-gauge) is used, a simple square knot can be tied and buried in the side of the tendinous tissue.
|FIG. 68-1 A satisfactory method of holding a tendon while sutures are being placed.|
|FIG. 68-2 The Bunnell-Meyer tendon suture pattern.|
When tying the suture, the surgeon must make sure that sufficient tension has been placed on both ends of the suture to create a slight buckling of the tendon tissue at the area of the anastomosis. This is important because the stumps have a tendency to retract slightly during the healing period and will separate if they are not brought into apposition with a slight buckle. When the procedure is completed, the edges of the cut tendons should not be visible. There should be slight buckling at the point of junction, and no suture material should be visible.
Small flat tendons can be repaired using the buttonhole overlapping technique (Fig. 68-3). This procedure has some disadvantages in that it creates a rather bulky area and cannot be used without shortening of the tendon. It has its greatest use in the application of a tendon graft. When using this technique it is essential that the tendon stumps be overlapped at least 1 cm. The buttonhole technique cannot be used within a tendon sheath because of the change in the circumference of the anastomosed area. This change in circumference is due to the over lapping of the tendon and the placement of sutures through two thicknesses of tendon (Fig. 68-4). Tendon sheaths are closely adapted to the tendon size. Therefore its use is limited to areas where tendons are moving through loose connective tissue and there is an abundance of paratendon.
|FIG. 68-3 Position of the tendons using the buttonhole overlapping suture technique.|
|FIG. 68-4 Placement of buttonhole sutures.|
Tendon contractures occur frequently. One must remember, however, that it is not the tendon that is contracted but the muscular attachment to the proximal end of the tendon. If the contracture is not too severe, continuos splintage in tension in a young animal may lengthen the tendon sufficiently to correct the muscular contracture. If, however, the contracture is severe, surgical intervention is necessary. In general, most cases of contracture involve the flexor tendons, with the exception of the common calcanean. The method of correction for this condition will be dependent upon the degree of contracture. The simplest procedure is tenotomy, in which the tendon is divided and allowed to retract. If the tendon retracts more than 3 cm the resulting union will be weak because of the thinness of the intervening bridge of tissue, which lacks the tensile strength of normal tendons. Therefore, if one anticipates that the tendon ends will retract more than 3 cm, a different technique should be used. Tenotomy is contraindicated within a tendon sheath because tendons do not regenerate within a sheath. If the surgeon is dealing with a contracture that is slight and he does not wish to do a complete tenotomy, the accordion method of lengthening can be useful. In this technique (Fig. 68-5) a series of cuts are made on opposite sides of the tendon approximately 2 cm apart. This will allow the tendon to stretch. It is imperative that the incisions in the sides of the tendon be of the same depth; if they are not, the tendon can tear completely through at its weakest point. The most common method of lengthening a tendon in cases in which it is necessary to lengthen it more than 3 cm is that of the Z tenotomy (Figs. 68-6 and 68-7), sometimes referred to as the half-section splitting and gliding method. In this procedure a vertical or longitudinal cut equal to the length the tendon will be extended is made in the center of the tendon. A transverse cut is then made at each end of the incision on the opposite sides of the tendon. This will make an elongated Z pattern. The ends of the tendon can then be reunited by sutures. A fourth technique (Fig. 68-8) is that of the oblique section and gliding in which the tendon is divided at an oblique angle. The more oblique the cut, the greater the distance the tendon can be lengthened. This method, however, is not practical on flat tendons, and the greater the lengthening of the tendon, the less area of opposing surface there will be when sutured. As a general rule, it is not advisable to reduce the opposing surface to less than half their original cross section.
|FIG. 68-5 The accordion technique for lengthening a tendon.|
|FIG. 68-6 The Z tenotomy technique for tendon lengthening.|
|FIG. 68-7 A modified Z tenotomy.|
|FIG. 68-8 The oblique section and sliding procedure.|
A fifth method is referred to as the Lange technique (Fig. 68-9). This method entails the placement of several transverse sutures through the tendon with subsequent division of the tendon through the sutures. The sutures are then tied, leaving a gap between the tendon ends. The sutures prevent further retraction of the stumps. This technique is feasible only outside a tendon sheath, since spontaneous regeneration between the ends will not occur within the sheath. The Lange technique can be used for repair of lacerated tendons in animals in whom part of the tendon is missing or necrotic and it is therefore impossible to approximate the ends of the tendon.
|FIG. 68-9 The Lange technique for lengthening tendons.|
An abnormally long tendon is generally a result of the breakdown of supporting structures and resultant strain on the tendon during the growth phase. It can also occur after severance when the joint is placed in hyperextension or flexion and the tendon regenerates during this immobilization period. There are several methods for shortening tendons, each of which is quite satisfactory (Figs. 68-10 through 68-13).
|FIG. 68-10 A Z incision with subsequent resection of tendon end for shortening tendons.|
|FIG. 68-11 Hoffa's method of shortening tendons.|
|FIG. 68-12 The doubling-over procedure.|
|FIG. 68-13 The wedge section excision for shortening tendons.|
Periodically animals are presented in whom severe atrophy of one or more groups of muscles has occurred, reducing their function to such a degree as to incapacitate the animal. In these cases it may be feasible to relocate a tendon from another muscle group to restore function.(6,15, 16) There are five principles that must be adhered to if tendon transfer or relocation is to be successful. (13)
The involved areas must be supple and joints must have a full range of passive motion. All reaction from the original trauma or subsequent manipulation must be resolved and the tissues must be in a normal state.
The muscle to be used to restore function must have sufficient strength to provide the desired motion and to be able to withstand the action of the antagonistic muscles.
The muscle to be used must have contractile movement to provide sufficient motion of the part. The amplitude should not be overdone to the point of providing a deformity in the opposite direction.
The muscle unit to be used must act in the proper direction, if it is at all possible. Altering the direction may be necessary and is possible, but such a change will always result in interference with the gliding mechanism. In addition, one must avoid passing the tendon through fascial planes or across raw fascial surfaces because adhesions will form and limit the amplitude of the tendon.
The integrity of a tendon must remain intact, that is, a tendon cannot be split to provide two motions of different directions or different amplitudes.
Another factor to be considered is that the tendon should not exert pressure on vessels or nerves when the muscle contracts. Under these circumstances these structures must be isolated and the tendon relocated beneath them. For a further discussion see Chapter 71.
There are two basic methods by which a tendon can be attached to bone. The first is by resecting a small piece of the periosteum from an area where the tendon is to be attached and placing the cut end of the tendon on the denuded area of bone. The tendon can then be sutured to the bone by passing a needle through the margins of the tendon and the adjacent periosteum. A second method, which is somewhat simpler, is to drill a small hole in the bone and place a Bunnell suture in the end of the tendon. The suture can then be pulled through the bone, drawing the tendon up against the periosteum. The suture is then fastened to the periosteum and other tissue. (4)
POSTOPERATIVE CONSIDERATIONS FOLLOWING TENDON SURGERY
It is essential that all tension be removed from the tendon during the healing period for the first 3 weeks. As a general rule tendons have little ability to hold sutures for the first 5 days after surgery, and the wound strength is not increased to any marked degree until after 14 days. At this point the strength increases rapidly.(11) Between 3 weeks and 6 weeks exercise should be quite restricted. Immobilization should be accomplished by cast application. If the tendon is a flexor or extensor tendon, the cast is applied in such a way that it reduces any stresses on the anastomotic area.
Contracture of the quadriceps is frequently associated with femoral fractures and has been termed a quadriceps tie-down. The choice of this term is unfortunate, however, because there are two separate entities. The true quadriceps tie-down is seen primarily in older dogs with fracture of the lower third of the femur in whom the fracture has been stabilized with some form of external splintage and the traumatized muscle has been incorporated into the fracture callus during the healing period. In this condition the proximal muscle is functional, and separation of the muscle tendon from the callus will allow flexion of the leg; however, if the tie-down has existed for some time, a long period of physical therapy must be instituted to reduce the joint stiffness that will occur in the stifle. True contracture of the quadriceps consists of muscle atrophy and subsequent replacement by fibrous connective tissue. It is thought to result as an injury to the cranial femoral artery as it enters the four heads of the quadriceps between the rectus femoris and the vastus medialis. This injury is seen most frequently in midshaft fractures of the femur in young growing animals and results in a bowstring effect as the muscle contracts and scars and the femur continues to grow, which in turn results in a hyperextension of the stifle (genu recurvatum). Subsequently, complete loss of function of the quadriceps mechanism occurs. Some authors have suggested a Z-plasty lengthening of the patellar tendon, but the results of this have generally been disappointing.(8) At present it is preferred to arthrodese the stifle at an angle that will permit walking.(1)
"Dropped muscle," a common greyhound injury, is the tearing of the gracilis muscle. This muscle is a sheathlike muscle or tendon located on the medial aspect of the leg. The muscle originates at the pubis synthesis and inserts in a fanlike tendon on the tibial crest. Dropped muscle is the term used when external changes are visible. The muscle fibers of the thickened portion become torn during strenuous action, and there is subsequent hemorrhage and hematoma formation, usually along the posterior border. These injuries are frequently not noticed until the day after the injury. The hematoma can be as large as an egg, and the animal continues to run poorly. In a period of time (3 weeks) scar tissue fills in at the site of the tear, and eventually these scars can be palpated as knots along the caudal border of the muscle tendon. If the animal is restricted, it frequently will become sound again; however, it is not uncommon that when the animal is raced a new injury will occur beside the old one. The principle for correction is lengthening of the scar tissue similar to the technique of lengthening the tendon in Figure 68-4 by the accordion method. When performing this procedure, the surgeon must take care not to cut muscle but only the fibrous scar tissue.
During the last few years a previously unreported condition of foreleg lameness has been brought to our attention:(5,7,14) contracture of the infraspinatus muscle. It is seen predominantly in working field dogs. The animal shows acute lameness, followed in a short time by continuous external rotation and abduction of the lower foreleg. By the time of presentation there is usually atrophy of the muscle and lack of pain in the shoulder. Clinical examination will reveal that the shoulder cannot be flexed if held in a normal position; however, if one rotates the lower leg outward and abducts it a small amount, full flexion can be achieved. This is due to the fact that one of the functions of this muscle is to rotate the leg outward and abduct it. Thus, if the muscle is contracted and fibrous, it allows only that movement of the lower limb. The muscle accomplishes this because it crosses the shoulder joint obliquely. Histologic examination of the affected muscle shows atrophy of the muscle bundles and replacement with fibrous tissues. In most cases the fibrous tissue is mature. The exact cause of this condition is unknown at this tame; however, from a histologic standpoint it resembles the ischemic contraction of Volkmann rather than a neuropathy. Surgical correction of the condition is a simple tenotomy of the tendon insertion and release of adhesions to the joint capsule if they exist. I find that simple reflection of the acromial portion of the deltoid in a caudal direction will expose the tendon of insertion as it inserts on the anterolateral aspect of the greater tubercle of the humerus. Return to normal leg function is immediate, and the prognosis for return to the field is excellent.
1. Bateman JK: Dropped thigh muscle in the racing greyhound. Vet Rec 76:201, 1964
2. Bunnell S: Primary repair of severed tendons. Am J Surg 47:502, 1940
3. Bunnell S: Surgery of the Hand. Philadelphia, JP Lippincott, 1944
4. Hauser C: A simple suture for repair of tendon to bone. Q Bull Northwest U Med 26:27, 1952
5. Hufford TJ, Olmstead JL, Butler HC: Contracture of the infraspinatus muscle and surgical correction in two dogs. J Am Anim Hosp Assoc 11:613, 1975
6. Jubb KV, Kennedy PC: Pathology of Domestic Animals. New York, Academic Press, 1963
7. Leighton RL: Tenotomy for infraspinatus contracture. Mod Vet Pract 58:134, 1977
8. Leighton RL: Quadriceps contracture (ischemic contracture of the quadriceps). Pathophys Small Anim Surg 98:831, 1981
9. Lipscomb P. Wakim J: Regeneration of severed tendons: An experimental study. Proc Staff Meet Mayo Clinic 36:271, 1961
10. Mason ML: Primary and secondary tendon suture. Surg Gynecol Obstet 70:392, 1940
11. Mason ML: Significance of function in tendon repair. Arch Phys Ther 22: 28, 1941
12. Peacock E: Morphology of homologous and heterologous tendon grafts. Surg Gynecol Obstet 109:735, 1959
13. Peacock E, Petty J: Antigenicity of tendons. Surg Gynecol Obstet 110:187, 1960
14. Pettit GD et al: Studies on the pathophysiology of infraspinatus muscle contracture. Vet Surg 7:8,1978
15. Pezzoli G: Sul trattamento chirurgico della paralisi del radiale nel cane: Recupero funzionale della mano paralitica mediante trapianti tendinei. Le Clinica Veterinaria 81: 345, 1958
16. Sterner W. Moller AW: Tendon transplantation: A surgical approach to radial paralysis in the dog. J Am Vet Med Assoc 137:71, 1960