Cruciate Ligament Rupture and Associated Injuries

Chapter 80

Steven P. Arnoczky


 


Section One: Stifle Kinesiology

The stifle joint represents the movable link between the femur and the tibia. In anatomical terms, the stifle is classified as a diarthrodial, condylar joint. Because of its complex motion and the presence of various intra-articular structures (cruciate ligaments and menisci), the stifle joint is, perhaps, the most complex joint in the body.

In the most basic terms, the bee movement of the femur relative to the tibia can be described by a set of three mutual orthogonal axes (x, by and z) (Fig. 80-1). The x axis passes through the femoral condyles parallel to the joint line in a medial-lateral direction. The y axis is parallel to the shaft of the tibia and passes through the medial tibial condyle just medial to the center of the tibial plateau. The z axis passes through the center of the joint space in a craniocaudal orientation.

Rotation about each axis, as well as translation (sliding) along each axis, results in six basic movements of the stifle joint (also termed the six degrees of freedom). While each motion (e.g., flexion-extension, varus-valgus angulation, axial rotation, cranial-caudal translation) may be present to some extent in normal stifle joint function, individual movements on or about a specific axis are limited by various ligamentous constraints:

X AXIS

Rotation: normal Sexton and extension of the stifle joint

Translation: prohibited by cruciate and collateral ligaments

Y AXIS

Rotation: axial rotation of the tibia on the femur; prohibited by the collateral ligaments (extension:internal and external rotation; flexion:external rotation) and limited by the cruciate ligaments (flexion:internal rotation)

Translation: prohibited by the cruciate and collateral ligaments in tension and the articular cartilage and menisci in compression

Z AXIS

Rotation: varus and valgus angulation; prohibited by the collateral ligaments

Translation: drawer movement; prohibited by the cruciate ligaments

Thus, abnormal movement on or about a specific axis indicates damage to the specified constraints.

In normal movement the stifle has a combined motion in two planes. Flexion and extension takes place about the x (or transverse) axis, while rotatory movement of the tibia on the femur occurs about the y (or longitudinal) axis. These rotatory motions are controlled by condylar geometry and ligamentous constraints. As the stifle is flexed (Fig. 80-2), the femoral and tibial attachments of the lateral collateral ligament move closer together and the ligament begins to relax. This allows a caudal displacement of the smaller lateral femoral condyle on the tibial plateau (rotation about the y axis) and results in an internal (medial) rotation of the tibia on the femur. Conversely, as the stifle is extended (Fig. 80-3), the lateral collateral ligament tightens and the lateral femoral condyle moves cranially on the tibial plateau, causing an external (lateral) rotation of the tibia on the femur. In humans, this motion has been classically termed the "screw-home" mechanism.(4,42)

Because of their anatomical relationship and spatial orientation within the joint, the cruciate ligaments begin to "twist" about one another as the stifle is flexed and the tibia internally rotates on the femur. This twisting action limits the amount of normal internal rotation of the tibia. As the stifle is extended, the cruciate ligaments "untwist" and therefore have no individual effect in limiting external rotation of the tibia.(4)

While the cruciate ligaments are considered dynamic structures for stability during stifle motion, the menisci are also dynamic and provide stability during the flexion-extension and rotatory movements of the joint. As the stifle is flexed, the menisci slide caudally on the tibial plateau (Fig. 80-4). Because of its attachments to the medial collateral ligament and joint capsule, the medial meniscus displaces considerably less than the more movable lateral meniscus. The caudal displacement of the lateral femoral condyle on the tibia during flexion makes the caudal displacement of the lateral meniscus even more pronounced and, in extreme movements of flexion, the meniscus may protrude over the edge of the tibial plateau. Conversely, as the stifle is extended, both menisci slide cranially on the tibial plateau. In general, flexion and extension takes place between the femur and menisci while rotational movements occur between the tibia and menisci.(5)

FIG. 80-1 Schematic drawing of the stifle joint of the dog shows the three axes of motion (x, y, and z)and their orientation

FIG. 80-2 As the stifle is flexed the lateral collateral ligament loosens, allowing internal rotation of the tibia on the femur. The cruciate ligaments "twist" on each other to limit this internal rotation. (Arnoczky SP, Torzilli PA, Marshall JL: Evaluation of anterior cruciate ligament repair in the dog: An analysis of the instant center of motion. J Am Anim Hops Assoc 13:553 558, 1977)

FIG. 80-3 As the stifle is extended, the lateral collateral ligament tightens and the tibia rotates externally. The cruciate ligaments "untwist" and thus have no effect on limiting external rotation. (Arnoczky SP, Torzilli PA, Marshall JL: Evaluation of anterior cruciate ligament repair in the dog: An analysis of the instant center of motion. J Am Anim Hops Assoc 13:553 558, 1977)

FIG. 80-4 Drawing of the dorsal aspect of the tibia illustrates the normal excursion of the menisci in extension and flexion (shaded). Note the limited movement of the medial meniscus. (Arnoczky SP, Torzilli PA, Marshall JL: Evaluation of anterior cruciate ligament repair in the dog: An analysis of the instant center of motion. J Am Anim Hops Assoc 13:553 558, 1977)

As the stifle joint flexes and extends, the axis of flexion of the femur (x axis) relative to the tibia does not remain constant. This is due to the geometry of the condyles and the structure of the ligamentous and muscular constraints. At any one instant, however, there is a point on the femur that has zero velocity with respect to the femur. This point constitutes the instant center of motion (Fig. 80-5).

FIG. 80-5 Determination of the instant center of motion. The points A and B displace to A' and B' respectively during the femoral motion shown. Their displacements are represented by the lines AA' and BB'. Perpendicular bisectors of these lines intersect at the instant center of motion (C) for the displacement shown. The positioning of the instant center on a line perpendicular to the articular surface at the point of joint contact (D), indicates that the articular surfaces will be sliding on each other with a relatively free and normal action. (Arnoczky SP, Torzilli PA, Marshall JL: Evaluation Of anterior cruciate ligament repair in the dog: An analysis of the instant center of motion. J Am Anim Hops Assoc 13:553-558, 1977)

An instant center that lies on the point of the articular surfaces results in a rolling motion of the joint. In this condition there is minimal friction loss or wear. If the instant center does not lie on the articular surfaces, but rather directly above it on a line perpendicular to the surface at the point of joint contact, there is a sliding motion of the articular surfaces. The least resistance to sliding motion will occur when the direction of velocity of the surface point is tangent to the contact surface (Fig. 80-5). In this instance the articular surfaces will be sliding on each other with a relatively free and normal action as the stifle moves. During normal flexion and extension of the stifle in the dog there is a combined rolling-sliding motion.(10)

Section Two: Cruciate Ligament Rupture

"Rupture of the anterior cruciate ligament is the most common injury in the stifle joint of the dog." (53)

Cruciate ligament rupture, especially cranial cruciate ligament rupture, has long been a clinical problem observed in veterinary practice. First described by Carlin in 1926, it was not until 1952 that Paatsama,(33) in his classic treatise on ligament injuries of the canine stifle, finally brought the clinical manifestations and surgical treatment of cruciate ligament rupture in the dog into focus. In the 30 years following that work, the diagnosis and surgical treatment of ruptured cruciate ligaments in the dog have received more attention in the veterinary orthopaedic literature than any other musculoskeletal problem, with the possible exception of hip dysplasia. In spite of all this information, the surgical treatment of cruciate ligament rupture continues to be a subject of discussion and investigation. It is the purpose of this chapter, therefore, to review the current concepts regarding cruciate ligament rupture and its surgical management.

Anatomy

The cranial cruciate ligament is attached to a fossa on the caudal aspect of the medial side of the lateral femoral condyle (Fig. 80-6). The ligament courses cranially medially and distally across the intercondylar fossa and attaches to the cranial intercondyloid area of the tibia (Fig. 80-7),(4,32) (These points of attachment are important when considering landmarks for intra-articular techniques of cranial ligament substitution.)

FIG. 80-6 (Left) Medial aspect of the lateral femoral condyle shows the area of attachment for the cranial cruciate ligament. (Right) Lateral aspect of the medial femoral condyle shows the area of attachment for the caudal cruciate ligament.

FIG. 80-7 Caudal surface of the tibia (left) and the dorsal surface of the tibial plateau (right) show the shape and relationship of the tibial attachments of the cranial and caudal cruciate ligaments.

The caudal cruciate ligament is attached to a fossa on the ventral aspect of the lateral side of the medial femoral condyle (Fig. 80-6). The caudal cruciate ligament passes caudodistally to the medial aspect of the popliteal notch of the tibia (Fig. 80-7).(l,32)

In general, the caudal cruciate ligament is slightly longer and broader than the cranial cruciate ligament. The caudal cruciate lies medial to and crosses the cranial cruciate ligament.(4,32) In flexion both ligaments twist on themselves and each other. The cranial and caudal cruciate ligaments are covered by synovium. This synovial covering provides the major blood supply to the ligaments (Fig. 80-8). These synovial or paraligamentous vessels give rise to smaller vessels that penetrate the ligament and freely anastomose with a network of longitudinal endoligamentous vessels.(5)

FIG. 80-8 Sagittal section of a stifle following arterial perfusion with India ink and tissue clearing Note the vascular contributions of the infrapatellar fat pad (FP) and posterior synovial tissues (PST) to the paraligamentous vessels of the cruciate ligaments (ACL, PCL). (P. patella; F. femur; T. tibia)

Function

The cruciate ligaments function as constraints of joint motion.(4) Specifically, the cranial cruciate ligament functions to prevent cranial displacement of the tibia on the femur, limit excessive internal rotation of the tibia on the femur by twisting on the caudal cruciate ligament, and prevent hyperextension of the stifle joint. The caudal cruciate ligament functions to prevent caudal displacement of the tibia on the femur and, in conjunction with cranial cruciate ligament, limits excessive internal rotation of the tibia on the femur.

Mechanism of Injury

The mechanism of cruciate ligament injury can be related directly to their function as constraints of joint motion. Excessive forces during extremes of these constraints will result in damage to the ligaments.

The most common mechanism of cranial cruciate ligament rupture is usually associated with a sudden rotation of the stifle with the joint in 20° to 50° of flexion. In this position the cruciate ligaments begin to twist on each other and on themselves to limit the normal internal rotation of the tibia on the femur. With excessive internal rotation of the tibia, the cranial cruciate ligament becomes wound very tightly and is subject to trauma from the lateral femoral condyle as it rotates against it.(5) This may cause the cranial cruciate ligament to rupture in its midportion or, in the case of younger animals, to avulse a portion of its bony attachment (Fig. 80-9). Another mechanism of injury to the cranial cruciate ligament is hyperextension. The cranial cruciate ligament is the primary check against hyperextension of the stifle.(4) Therefore, as the stifle is hyperextended, the cranial cruciate ligament is the first structure to be subject to injury. Rupture of the caudal cruciate ligament alone is rare and is usually associated with severe trauma or dislocation of the stifle joint. This is probably due to the fact that, with the exception of caudal displacement of the tibia, the caudal cruciate ligament is protected from extremes of motion by other joint structures.(5) Direct trauma to the tibia in a craniocaudal direction, however, would place severe stress on the caudal cruciate ligament and may result in its rupture (Fig. 80-10).

FIG. 80-9 Lateral radiograph of a stifle of a young dog demonstrates an avulsion fracture (arrow) of the cranial cruciate ligament.

FIG. 80-10 Lateral radiograph of a stifle of a dog demonstrates caudal displacement of the tibia as a result of rupture of the caudal cruciate ligament. Note the abnormal position of the fabella relative of the tibial plateau.

Degenerative Cruciate Lesions

While acute cruciate ligament rupture due to trauma does occur, it is thought that the majority of cruciate lesions are a result of chronic degenerative changes within the ligaments themselves. Variations in conformation, valgus (knock-knee) and varus (bowleg) deformities of the stifle, and repeated minor stresses can result in progressive degenerative joint disease. These changes are frequently bilateral and have been referred to as postural arthrosis.(39) Patellar luxation is a common problem that contributes to excessive stress on the cranial cruciate ligament owing to the fact that the stifle lacks the proper support of the quadriceps muscles and patellar ligament. In obese animals these stresses are increased and the possibility of degenerative joint changes is greater. As joint changes develop, the cruciate ligaments undergo alteration in their microstructure.(44) Collagen fibrin become hyalinized, and the tensile strength of the ligament is reduced, making the ligament more susceptible to damage from minimal trauma. These changes also have been associated with the aging process and may explain the fact that the majority of cruciate injuries are seen in dogs over 5 years of age.(22)

Pathology of the Cruciate Insufficient Joint

Rupture of either or both cruciate ligaments produces marked instability of the stifle joint, resulting in pain and lameness.(28) This instability also leads to progressive degenerative changes within the joint. Clinical(30,37) and experimental(3,28,29) observations have demonstrated that these changes consist of periarticular osteophyte formation, capsular thickening, and meniscal degeneration (Fig. 80- 11). Long-term evaluation of cruciate insufficient joints in dogs reveals that as periarticular and capsular changes progress, the joints become less unstable.(29) While some of the clinical signs were found to subside with the decreasing instability, the severe degenerative changes already present within the joint would suggest that in most instances early surgical repair is preferable to long-term conservative therapy.

FIG. 80-11 Lateral and anteroposterior radiographs of a stifle 6 months following experimental transection of the cranial cruciate ligament. Note the presence of osteophytes on the tibial condyles and in the intercondylar notch of the femur.

Diagnosis of Cruciate Ligament Injury

Rupture of the cranial or caudal cruciate ligament or both usually presents as an acute hind-leg lameness and is diagnosed by demonstrating cranial-caudal instability of the stifle joint (drawer sign). The cranial cruciate ligament is best evaluated for integrity with the limb in slight flexion (Fig. 80-12). With the limb in this "functional position," one attempts to subluxate the tibia cranial to the femur, eliciting the cranial drawer sign, which is present only when cranial cruciate insufficiency exists. In some painful acute injuries in large dogs and in chronic cases in which muscle guarding or fibrosis can occur, respectively, the cranial drawer sign may be difficult to elicit. In these animals sedation or general anesthesia may be necessary to properly evaluate the stifle joint. Another method of diagnosing cranial cruciate ligament rupture is the tibial compression test.(20) In this maneuver the examiner grasps the metatarsus with one hand and places the palm of the hand over the cranial aspect of the distal femur and patella, extending the forefinger down over the tibial tuberosity. By flexing the hock, the reciprocal tightening effect of the gastrocnemius muscle acts to compress the tibia and the femur. If the cranial cruciate ligament is not intact, the tibial tuberosity will be felt to slide cranially.

Rupture of the caudal cruciate ligament is diagnosed best by the caudal drawer test. The leg is grasped in a manner similar to the cranial drawer test and the examiner attempts to subluxate the tibia caudally on the femur.

FIG. 80-12 Photograph shows the placement of the examiners hands on the distal femur and proximal tibia for proper evaluation of drawer motion. The examiner attempts to subluxate the tibia on the femur.

In some larger dogs in whom muscle guarding may mask the cranial or caudal drawer movement, the presence of increased internal rotation of the tibia on the femur associated with cruciate ligament rupture may also be used to confirm the diagnosis of ligament insufficiency. It is important to note, however, that the increased internal rotation can be present with cranial or caudal cruciate ligament rupture.(4)

Cruciate Ligament Repair

As noted above, rupture of either or both cruciate ligaments produces joint instability, which, if left untreated, will result in progressive degenerative changes within the joint. It is for this reason that conservative, nonoperative therapy usually does not produce satisfactory results, and therefore surgical intervention is indicated in most cases. In some chronic conditions of cruciate ligament rupture in older dogs, however, severe degenerative joint changes may dictate a less favorable prognosis following surgical repair. In these animals, conservative management with anti-inflammatory drugs or analgesics may provide adequate palliative care. Also, concurrent generalized joint disease (e.g., rheumatoid arthritis, systemic lupus erythematosus) may obviate the repair of a cruciate insufficient joint.

Surgical repair of the cruciate ligaments has undergone considerable development in the last 30 years,(25) and a comprehensive review of the techniques and materials used for the repair or reconstruction of the cruciate insufficient stifle can leave one bewildered and confused. Basically, the surgical procedures for cruciate ligament repair can be divided into the intraarticular and the extra-articular techniques. The intra-articular techniques use either an autogenous or a synthetic graft to actually replace the cruciate ligament (l,2,7,9,11,15,17,18,21,23,24,27,33,38-41,43) while the extra-articular techniques stabilize the joint by altering (tightening) extra-articular structures.(12-14,16,19,22,31,34-36) Before the individual techniques for cruciate ligament repair are discussed, it should be noted that in all cases of cruciate ligament repair, the joint should be opened by lateral or medial arthrotomy and inspected thoroughly for additional pathology. The remnants of the ruptured ligament should be removed and the joint irrigated thoroughly with lactated Ringer's or saline solution. If the joint has been unstable for a while, marginal osteophytes will be present along the margin of the femoral trochlea.(28) These osteophytes may be removed by sharp dissection with a scalpel blade if they appear too proliferative.

CRANIAL CRUCIATE LIGAMENT

Extra-articular Techniques

While there are many techniques for the extra-articular surgical repair of the cranial cruciate ligament, the basic principle of the repair is the same for all. The majority of extra-articular techniques involve imbrication (tightening) of the lateral joint tissues with one or more sutures. The sutures are placed in a general anteroposterior orientation to eliminate the cranial displacement of the tibia on the femur (cranial drawer). By placing the imbrication suture or sutures on the lateral aspect of the joint, the tendency for inward rotation of the tibia due to cranial cruciate ligament insufficiency is also prevented. In a study comparing the biomechanics of normal joint motion with those of a joint in which imbrication sutures were used, it was found that the imbrication techniques placed additional constraints on joint motion (i.e., eliminated the small amount of internal rotation of the tibia on the femur normally present when the joint is flexed).(10) These constraints resulted in abnormal joint motion at the point of articular contact. It is thought that while these constraints are tolerated by smaller dogs (<30 lb), larger dogs generate sufficient force to overcome the constraints. This may explain the inconsistent results observed in the larger breed dogs in whom extra-articular techniques have been used.

CAPSULAR (FASCIAL) IMBRICATION (PEARSON).(35,36) An early extra-articular technique describes the use of multiple Lembert sutures in the lateral joint tissues. Following a routine lateral arthrotomy, the joint is inspected and flushed as noted above. The joint capsule is then closed with small Lembert sutures using a nonabsorbable suture material. The stifle joint is stabilized by placement of three layers of large Lembert sutures in the muscle fascia and fibrous layers of the joint capsule (Fig. 80-13). The first of these layers is started on the lateral surface of the stifle joint 1.5 cm to 2 cm above the patella and terminated in the area of the tibial tuberosity. The Lembert sutures are about 1 cm apart and placed in such a way that the first portion of the suture is one third the distance from the cranial to the caudal border of the stifle joint (near the convergence of the fascia lata and the biceps femoris muscle), and the second portion of the suture is placed just lateral to the edge of the patella and patellar ligament. This layer contains six to eight Lembert sutures.

A second layer of two to four large Lembert sutures is placed on the lateral side of the stifle joint, concentrating on the area between the patella and the tibial tuberosity.

A layer of two to four large Lembert sutures is then placed in the medial aspect of the stifle joint. These sutures are also concentrated in the area between the patella and tibial tuberosity. One portion of the Lembert suture is one third the distance from the cranial to the caudal border of the stifle joint (near the area of the caudal portion of the sartorius muscle) and the second portion of the suture is placed just medial to the edge of the patella and patellar ligament.

The fascia and skin are closed in a routine manner. The limb is placed in a soft padded bandage and the animal confined to limited exercise for 2 to 3 weeks.

FIG. 80-13 Capsular (fascial) imbrication. (a) The joint capsule is closed with interrupted Lembert sutures. (b) Additional layers of imbricating Lembert sutures are placed in the fascial tissues.

LATERAL RETINACULAR IMBRICATION (DeANGELIS).(14) Another imbrication technique uses a single mattress suture of heavy (No. 1 or No. 2) nonabsorbable material placed on the lateral aspect of the joint. Following lateral arthrotomy, the suture material is passed behind the lateral fabella and into the dense connective tissue surrounding it (Fig. 80-14, a). The suture is then directed craniodistally, where it is passed into the lateral third of the patellar ligament just proximal to its insertion on the tibial tuberosity. The suture material is reinserted into the ligament about 3 mm from its point of emergence and directed so as to exit near the original point of entry (Fig. 80-14, b). The limb is placed in a functional position and the suture tightened (Fig. 80-14, c). This suture should eliminate the cranial drawer movement completely. If a slight cranial drawer movement is still present, an additional mattress suture, placed parallel and as close as possible to the first suture, can be used to eliminate the remaining drawer movement. If appreciable drawer movement exists after placement of the first suture, the suture should be removed and replaced. It should be noted that the fibular nerve passes caudal to the lateral fabella, and appropriate caution should be used when placing the suture in this area.

If the patellar ligament is damaged or for some reason will not support the imbrication suture, a drill hole can be placed in the proximal aspect of the tibial crest and the suture passed through it.

The joint capsule and skin are closed routinely. The limb is placed in a soft padded bandage for 2 weeks and the animal is confined to limited exercise for this period.

FIG. 80-14 Lateral retinacular imbrication. (a) Placement of imbrication suture in the connective tissue surrounding the lateral fabella. (b) The suture is directed craniodistally and into the lateral third of the patellar ligament toward the lateral fabella. (c) The suture is passed into the connective tissue caudoventral to the lateral fabella and tied with the limb in a functional position. (Arnoczky SP: Surgery of the stifle: The cruciate ligaments. Compendium on Continuing Education for the Small Animal Practitioner 2:106-116,1981)

MODIFICATION OF THE LATERAL RETINACULAR IMBRICATION TECHNIQUE (FLO).(19) A modification of the lateral retinacular imbrication technique involves the use of single imbrication sutures on the medial as well as lateral aspect of the stifle joint. In this technique the heavy, nonabsorbable sutures are placed around the fabellae and through a drill hole in the tibial crest as described above. Once these sutures are preplaced, the limb is put in a functional position and the lateral suture is tightened first to externally rotate the tibia and thereby limit internal rotation. The medial suture is then tightened and together with the lateral suture acts as a "sling" to prevent cranial drawer motion (Fig. 80-15). Following routine closure, the limb is placed in a modified Robert Jones bandage for 2 weeks.

Another modification of this techniques(35) uses two to four Lembert sutures of nonabsorbable suture material placed in the medial and lateral joint capsule to further tighten and stabilize the stifle joint.

FIG. 80-15 Placement of the lateral and medial imbrication sutures around the fabellae and through a drill hole in the tibial crest. Note that the lateral imbrication suture is always tied first. (Arnoczky SP: Surgery of the stifle: The cruciate ligaments. Compendium on Continuing Education for the Small Animal Practitioner 2:106 116, 1981)

POSTEROLATERAL CAPSULORRHAPHY (HOHN).(22) Another procedure using both medial and lateral support of the stifle is the posterolateral capsulorrhaphy. Following medial arthrotomy, the joint is explored and the capsule closed routinely. The caudal sartorius muscle is transected at its insertion and advanced to the proximal aspect of the patellar ligament where it is sutured with chromic gut (Fig. 80-16, a). The lateral aspect of the joint is approached extracapsularly and the caudolateral joint capsule identified. A small incision is made in the caudolateral joint capsule parallel to and at the level of the joint line. This incision is closed with two mattress sutures of the nonabsorbable material with the joint in flexion and external rotation (Fig. 80-16, b). An additional tension suture is placed through the distal end of the lateral collateral ligament and around the lateral fabella. This suture is also made with the joint in external rotation and flexion and will provide additional stability while the capsular plication is healing. The biceps tendon and fascia lata are then plicated over the patellar tendon with interrupted mattress sutures Of nonabsorbable material (Fig. 80-16, c). These sutures are tied with the joint in extension. Thus, the instability of the Joint is checked by the active constraints of the medial and lateral muscle advancement as well as by the passive constraints of the caudal capsular imbrication. Following this procedure, the animals are confined to the house or a leash for 3 weeks. In larger animals a Kirschner apparatus is used to span and immobilize the joint. This is usually removed at 3 weeks.

FIG. 80-16 Posterior lateral capsulorrhaphy. (a) Following medial arthrotomy and inspection of the joint, the insertion of the posterior sartorius muscle is dissected free. (b) The joint capsule is then closed and the posterior sartorius muscle advanced to the patellar tendon, where it is sutured. (c) A small incision is made in the posterior lateral joint capsule and is closed with imbricating sutures. An additional tension suture is placed through the distal end of the lateral collateral ligament and around the lateral fabella. (d) The biceps tendon and fascia lata are then plicated over the patellar tendon.

Intra-articular Techniques

The use of autogenous material has long been advocated for the anatomical replacement of the cranial cruciate ligament. Fascia lata,(33) skin,(27) and patellar ligament(9,17) have all been used as replacement material. The basic technique involves the re-creation of an intra-articular structure in the approximate spatial orientation of the normal cranial cruciate ligament. Thus the graft can function like the normal ligament to prevent cranial drawer motion, hyperextension of the stifle, and, by twisting with the caudal cruciate ligament, to limit internal rotation of the tibia on the femur. The graft is usually passed through drill holes in the femur and tibia and, depending on the technique used, is attached to the soft tissues of the femur or tibia.

FASCIA LATA (PAATSAMA).(33) Perhaps the most commonly used intra-articular technique is that described by Paatsama. Modified from a technique used in humans, this procedure has provided the basis for most intraarticular techniques used in veterinary medicine.

The stifle is approached through a lateral parapatellar skin incision that extends from the proximal third of the femur to the level of the tibial tuberosity. The fascia lata is then incised to create a strip of tissue at least 1 cm wide in medium size dogs and up to 1.5 cm to 2 cm wide in large dogs. The incision is started over the lateral collateral ligament and is continued proximally, following the cranial edge of the biceps femoris. This incision forms the caudal edge of the fascial strip and extends proximally to the level of the fascia lata muscle. A parallel incision is made an appropriate distance cranially and extends the length of the first incision (Fig. 80-17,a). The fascial graft is transected at its proximal attachment, cleaned of all fat and muscle tissue, and placed under the skin or wrapped in saline-soaked sponge to prevent drying.

The stifle is exposed through a routine lateral arthrotomy and the joint inspected. A hole is made in the lateral femoral condyle using an intramedullary pin or drill bit. This femoral "tunnel" is drilled from a point above the femoral insertion of the lateral collateral ligament through the condyle to the femoral insertion of the cranial cruciate ligament. A tibial tunnel is drilled from the medial border of the tibial crest obliquely upward to the tibial insertion of the cranial cruciate ligament. The fascial graft, which is still attached distally, is pulled through the femoral and tibial tunnels with the aid of a thin wire loop (Fig. 80-17,b). With the joint in a functional position the fascial transplant is pulled taut to eliminate any cranial drawer movement. The free end of the graft is sutured to the tibial attachment of the patellar tendon. The joint capsule and fascial incision are closed routinely.

In some modifications of the technique, the capsule and fascial incisions are imbricated with nonabsorbable Lembert sutures, and a lateral retinacular imbrication suture is added to provide additional stability.(39)

Postoperatively the limb is placed in a soft padded bandage or splint for 2 to 3 weeks.

> FIG. 80-17 Fascia lata substitution (Paatsama). A strip of fascia lata 1.5 cm to 2.0 cm is harvested (a) and passed through drill holes in the femur and tibia (b).

MODIFIED FASCIA LATA TECHNIQUE (DICKINSON AND NUNAMAKER).(15) A modification of the Paatsama technique uses a fascial graft passed through the joint from the lateral aspect of the proximal tibia and through a femoral drill hole (Fig. 80-18).

The graft is harvested in a manner similar to that described for the Paatsama technique. Following a routine lateral arthrotomy a drill hole is made in the femur using a 5/32" to 1/4" Steinmann pin. The stifle is flexed to 90° and the intramedullary pin introduced obliquely into the intercondylar notch to enter at the femoral origin of the cranial cruciate ligament and exit just lateral to the proximal end of the lateral trochlear ridge. The drill hole is extended through the joint capsule and distal fibers of the vastus lateralis muscle. The fascial graft is passed through the femoral tunnel with the aid of a wire loop and, with the limb in a functional position, the fascial strip is secured to the fascial incision over the joint using heavy (No. 1) monofilament nylon. Following routine closure of the joint capsule and skin, the limb is immobilized in an external splint for 2 weeks.

FIG. 80-18 Modified fascia lata substitution technique. (a) A graft of fascia lata is harvested as in the Paatsama technique. (b) A drill hole is made in the femur at the origin of the cranial cruciate ligament. (c) The fascial graft is pulled through the joint and through the femoral tunnel. (d) The graft is sutured back on itself at the level of the tibial tuberosity

PATELLAR TENDON TECHNIQUE (DUELAND).(17) In the patellar tendon technique the middle third of the patella-patellar tendon complex is harvested and used as the replacement material. Following routine lateral arthrotomy and joint exploration, two parallel incisions are made in the patellar ligament isolating the middle one third of the ligament. These incisions are extended over the patella and with the quadriceps fascia for a distance of 2 cm to 4 cm. A V-shaped wedge of bone is removed from the cranial aspect of the patella using a fine bone saw. Extreme care must be taken so as not to disturb the articular surface of the patella or the fascial and ligamentous attachments to the bone wedge. The strip of tissue with the patellar wedge attached is then freed. proximally and passed through the joint (Fig. 80-19, a). A femoral drill hole is made in the lateral femoral condyle using a Steinmann pin. The pin is placed through the joint obliquely, entering the condyle at the femoral origin of the cranial cruciate ligament and exiting the posterior lateral aspect of the condyle. The fascial-patella-patellar ligament graft is then pulled through the joint and into the femoral tunnel with the aid of a guide wire. The limb is placed in a functional position and the graft pulled taut and sutured to the lateral aspect of the femoral condyle with nonabsorbable sutures. A small pin passed through the tunnel and patellar bone wedge is also used to provide additional anchorage (Fig. 80-l9,b). Following routine closure the limb is placed in a soft padded bandage or splint for 3 to 4 weeks.

Proper graft orientation is critical to the function of the cranial cruciate replacement and therefore the correct placement of the femoral drill hole is essential if the graft is to remain functional throughout the range of motion. Improper placement may result in fatigue and ultimate failure of the grafted material (Fig. 80-20). With most intra-articular replacement procedures, the position of the graft varies with the surgeon or the technique. Another procedure minimizes the variability of this graft replacement by eliminating the femoral drill hole and passing the graft over the top of the lateral femoral condyle (Fig. 80-21).

FIG. 80-19 Patellar tendon substitution (Dueland). (a) The median one-third of the patella-patellar tendon complex is harvested and used as the graft material. (b) Attached at the tibial tuberosity, the graft is pulled through the joint and through a drill hole in the lateral femoral Condole. A pin can be placed through the drill hole and patellar wedge to further anchor the graft.

FIG. 80-20 Schematic drawing of the stifle showing the change in length of the intra-articular graft from extension (A-B) to flexion (A'-B') when the femoral drill hole is placed improperly. (Arnoczky SP, Tarvin GB, Marshall JL et al The over-the-top procedure. A technique for anterior cruciate ligament substitution in the dog J Am Anim Hops Assoc. 15:28>290, 1979)

FIG. 80-21 Schematic drawing of the stifle showing no change in length of the intra-articular graft from extension (A-B) to flexion (A'-B'-) when the graft is placed in the "over-the-top" position. (Arnoczky SP, Tarvin GB, Marshall JL et al: The over the-top procedure: A technique for anterior cruciate ligament substitution in the dog. J Am Anim Hops Assoc 15:28>290, 1979)

THE OVER-THE-TOP TECHNIQUE (ARNOCZKY).(9) in the over the-top procedure the medial one third of the patella-patellar ligament complex is isolated by a longitudinal incision in the ligament and an osteotomy of the anteromedial aspect of the patella (Fig. 80-22,a and b). The incision is carried proximally into the fascia lata. The length of the incision proximal to the patella should be at least one and a half times the distance of the patellar tibial tuberosity to ensure adequate graft length. A parallel incision is then made to free the graft, leaving it attached to the tibial tuberosity (Fig. 80-22,c). A vertical incision is made in the lateral femoral fabellar ligament and, with the joint in hyperflexion, a curved hemostatic forceps is inserted into the incision and passed into the intercondylar notch of the femur taking care to preserve the posterior joint structures by staying close to the bone. The tips of the forceps are manipulated until they can be visualized within the joint, lateral to the caudal cruciate ligament (Fig. 80-22,d). A stay suture is placed in the proximal portion of the graft and the graft is pulled gently through the joint and over the top of the lateral femoral condyle. Flexing and extending the joint during this maneuver will facilitate the passage of the graft. Once the graft is in position, it is held under gentle traction and the joint is tested for cranial drawer movement. All craniocaudal instability should be eliminated throughout the range of motion with the graft in place. The graft is attached to the soft tissues of the lateral femoral condyle with simple interrupted sutures of 3-0 stainless steel (Fig. 80-22,e). Following routine closure the animal is placed in a soft padded bandage for 2 to 3 weeks. In larger dogs (>60 lb), a lateral plaster of paris splint is added for the first 2 postoperative weeks.

A modification of the over-the-top technique uses fascia lata(33*) or a composite of fascia lata lateral retinacular tissue and the lateral one third of the patellar tendon(23) for the intra-articular graft. The grafted tissues are harvested in a manner similar to that described for the Paatsama technique. With the fascial or composite fascial tissue left attached at the proximal lateral tibia region, the graft is pulled through the joint and over the top of the lateral condyle (Fig. 80-23). With the joint in a functional position, the fascial strip is pulled taut and secured to the femur by suturing the fascial strip to the patellar tendon and joint capsule. A lateral retinacular imbrication suture of heavy nonabsorbable material is then placed from the lateral fabella to the insertion of the patellar ligament to further stabilize the joint and "protect" the grafted tissues until they heal.

Following routine closure the limb is placed in a soft padded bandage, and exercise is restricted for 2 to 3 weeks.

It has been shown that following transplantation both the patellar ligament(8) and fascial composite grafts(23) undergo a degenerative process. This is followed by revascularization of the graft and a regenerative response. This revascularization originates from the soft tissues of the infrapatellar fat pad and synovium. Because of this it is advisable to preserve the fat pad and suture it to the intra-articular grafts to optimize revascularization and graft viability.

* Parkes L: Personal Communication, 1980, and Piermaitei DL: Personal communication, 1980.

FIG. 80-22 Over-the-top technique (Arnoczky). (a) The medial one-third of the patella-patellar ligament complex is isolated and the incision is extended proximally into the fascia lata. Note the placement of the osteotome to remove a craniomedial wedge of bone (b) with the patellar ligament attached. (c) The graft is freed by a parallel incision but left attached at the tibial tuberosity. (d) With the limb in flexion, a hemostat is passed from the caudolateral aspect of the lateral femoral condyle into the intercondylar notch. (e) After the graft material is passed through the joint and "over-the-top" of the lateral condyle, it is attached to the soft tissues of the condyle with interrupted sutures of 3-0 stainless steel. (Arnoczky SP: Surgery of the stifle: The cruciate ligaments. Compendium on Continuing Education for the Small Animal Practitioner. 2:106 116, 1981)

FIG. 80-23 The fascial graft is harvested, as noted previously, and pulled through the joint (a) and over-the-top of the lateral femoral condyle (b).

SYNTHETIC CRUCIATE LIGAMENTS. The use of synthetic prosthesis for the intraarticular replacement of the cruciate ligaments has long been the goal of both veterinary and human orthopaedists. Many materials, including nylon,(43) Teflon,(11) and Dacron(38) have been tried, but none has proved to be effective. Strande summarized the problem in 1967: "The ideal transplant material has not yet been found. Ideally it should possess great strength, a little elasticity, and should tolerate wear and tear in the joint for several months and be non-irritant. "(41) The search for such a material continues.

CAUDAL CRUCIATE LIGAMENT REPAIR

Repair of caudal cruciate ligament rupture has received little attention in the veterinary literature. As noted above, isolated caudal cruciate ligament rupture is uncommon; it is usually associated with concurrent ligamentous injuries of the stifle.

Femoral avulsion injuries of the caudal cruciate ligament can be treated primarily by reattaching the avulsed portion of bone. Depending upon the size of the avulsed bone, it can be reattached using a bone screw(26) or heavy wire mattress sutures passed through the avulsed bone and though drill holes in the medial femoral condyle. The wire sutures are then tied snugly on the outer aspect of the medial condyle.

Extra-articular imbrication of capsular tissues has been used to treat cases of caudal cruciate ligament rupture in smaller animals.(13) Imbrication sutures are placed on the lateral and medial aspects of the joint in a craniocaudal direction from the proximal aspect of the patella to the proximal caudal aspect of the tibia (Fig. 80-24). These sutures will tighten the joint capsule and prevent caudal displacement of the tibia on the femur as well as the abnormal internal rotation of the tibia due to the caudal cruciate rupture. Following routine closure the limb is placed in a soft padded bandage for 2 to 3 weeks.

FIG. 80-24 Caudal cruciate ligament stabilization. Lateral view of the stifle joint shows the placement of imbrication sutures. (Note: additional imbrication sutures are placed on the medial aspect of the joint in a similar manner.) (Arnoczky SP: Surgery of the stifle: The cruciate ligaments. Compendium on Continuing Education for the Small Animal Practitioner 2:106 116, 1981)

Because caudal cruciate ligament rupture is usually associated with other ligamentous injuries, the re-establishment of joint stability may require a composite of extra-articular and intra-articular techniques. Ingenuity and a thorough knowledge of stifle joint mechanics is important when treating these combined instabilities.

Section Three: Meniscal Injury

Anatomy

The menisci are biconcave, C-shaped disks of fibrocartilage interposed between the condyles of the femur and tibia. In extremely rare instances the lateral meniscus may appear discoid.(46) The menisci are held in position by six meniscal ligaments (Fig. 80-25). The lateral meniscus is attached to the tibia by cranial and caudal meniscotibial ligaments. The caudal horn of the lateral meniscus is also attached to the lateral aspect of the medial femoral condyle by means of the femoral ligament of the lateral meniscus. The medial meniscus is attached to the tibia by cranial and caudal meniscotibial ligaments. An intermeniscal ligament joins the cranial horns of the lateral and medial menisci and lies just cranial to the tibial attachment of the cranial cruciate ligament.(5)

The medial meniscus also has a fibrous attachment to the medial (tibial) collateral ligament, and its peripheral margins are attached to the joint capsule by coronary ligaments. The lateral meniscus is loosely attached to the joint capsule at its periphery but has no collateral ligament attachment. Thus, the medial meniscus is firmly attached while the lateral meniscus is more movable.(5,44)

FIG. 80-25 Drawing of the dorsal aspect of the tibia illustrates the menisci and their attachments.

While the exact function of the menisci remains unclear, their role in protecting the joint Surfaces and maintaining joint stability makes them important structures in the complex biomechanics of the stifle.

Meniscal Injury

The most common meniscal injury occurs in the medial meniscus and is associated with rupture of the cranial cruciate ligament.(5,39,47,51,53) When this ligament is ruptured, there is an abnormal increase in the internal rotation of the tibia on the femur. This increase in rotation causes the medial femoral Condole to place an excessive twisting force on the relatively immobile medial meniscus. The twisting action may stretch the concave inner border of the meniscus and tear it in a transverse fashion (Fig. 80-26,A). in some cases, the meniscus is crushed between the medial femoral Condole and the medial tibial condyle. When a rotational force is added, a longitudinal tear in the medial portion of the meniscus may result (Fig. 80-26,B). A longitudinal tear that displaces its medial portion into the joint is called a "bucket-handle" tear (Fig. 80-26,C). In extreme flexion, the caudal horn of the medial meniscus is compressed between the femur and tibia and can be easily damaged. In this position, rotational forces may tear the caudal attachment of the medial meniscus, allowing its caudal horn to move about freely (Fig. 80-26,D). in some instances, the freely moving segment of the meniscus in a caudal horn tear or bucket-handle lesion may displace into the joint and interfere with flexion or extension.

FIG. 80-26 Drawing of the medial meniscus illustrates a transverse tear (A), a longitudinal tear (B), a "bucket-handle" tear (c), and a caudal horn tear with folding over of the caudal horn (D).

Reports of lateral meniscal injury are rare and are usually associated with massive joint trauma. The loose connection of the lateral meniscus to the joint capsule and the absence of collateral ligament attachment make it less likely to be caught between the femoral and tibia condyles than the less mobile medial meniscus.

While meniscal injury can occur in conjunction with acute cranial cruciate ligament rupture, a higher percentage of meniscal lesions are associated with chronic joint instability.(45) These degenerative meniscal lesions develop even when there is no primary meniscal injury. Joint instability produces an unphysiologic gliding and shearing motion that can squeeze the menisci between the femur and tibia and cause them to degenerate (Fig. 80-27). The microstructure of the fibrocartilage is altered and the menisci are more vulnerable to injury and may tear with minimal trauma.(45)

FIG. 80-27 Photograph shows a degenerative lesion of the medial meniscus 6 months following experimental transection of the cranial cruciate ligament.

Diagnosis

As noted above, injury to the meniscus usually occurs in association with rupture of one or both of the cruciate ligaments. In the case of caudal horn tears, or detachments, of the medial meniscus the instability resulting from cruciate ligament insufficiency may cause the caudal horn of the meniscus to fold on itself as the medial femoral condyle passes over it.(39,53) This action may produce a "clicking" or "snapping" sound and is said to be diagnostic of meniscal injury.(39) While such a sign may be suggestive of meniscal damage, it is my opinion that the meniscus can be accurately evaluated only by arthrotomy and visualization throughout the range of motion. By flexing and extending the opened joint and applying a cranial or caudal stress to the tibia, lesions of the caudal horn of the meniscus should become apparent. In some cases of cranial cruciate ligament rupture in which the caudal attachment of the medial meniscus has been stretched, the caudal horn may be seen to displace cranially upon flexion of the stifle.(53) This does not necessarily indicate damage to the meniscus, since it will usually return to its normal position upon extension of the joint. These lesions should be evaluated carefully to avoid unwarranted removal of the meniscus.

Meniscectomy

Indications for meniscectomy have been the subject of controversy. While further study is needed to identify and define the exact sequelae of meniscal injury in the stabilized joint, it is my opinion that only menisci exhibiting caudal horn detachments, severe longitudinal tears, or complete disruption warrant meniscectomy. Partial transverse tears or isolated peripheral detachments appear to do well clinically in the stabilized joint and therefore need not be removed. In most instances, however, I advocate a partial meniscectomy with removal of only the damaged portion of the meniscus.

Since most meniscal injuries are associated with cranial cruciate ligament injury, the meniscus is approached through a routine lateral or medial arthrotomy. When the cranial cruciate ligament is ruptured, the stifle joint can be subluxated to permit greater exposure of the meniscus (Fig. 80-28). Both medial and lateral menisci should be examined through the range of motion. By placing a small amount of cranial drawer on the joint during these manipulations, lesions of the caudal horn of the medial meniscus should become apparent. If no obvious tears or fractures of the menisci are found, the meniscal attachments should be checked to make sure they are intact. Localized lesions of the free edge (concave margin) of the meniscus (i.e., bucket-handle lesions) can be removed by partial excision with a fine-pointed scalpel blade (47,52) (Fig. 80-28,B). This will leave the peripheral portion of the meniscus intact and may preserve some of the mechanical function of the meniscus. Severe damage to the meniscus will necessitate its total removal.(39,47,51,52) A knowledge of the anatomical attachments of the meniscus will facilitate its removal. The cranial meniscotibial and intermeniscal ligaments should be severed and grasped with a small rat-toothed forceps. With gentle traction applied to the meniscus, the convex peripheral margin of the meniscus is dissected free from its attachment, a procedure accomplished best with a No. 15 Bard-Parker blade or a No. 64 Beaver miniblade. Care should be taken to avoid laceration of the articular cartilage of the femur or tibia. The caudal meniscal attachment is then severed and the meniscus removed. Dissection in this caudal compartment of the joint should not be overly zealous, since the popliteal artery lies immediately caudal to the caudal attachment of the medial meniscus.

FIG. 80-28 (A) Drawing of the stifle shows the ruptured cranial cruciate ligament and longitudinal tear of the medial meniscus. (B) By pulling the tibia cranially, the meniscal lesion becomes exposed and can be removed easily by partial excision.

While most veterinary surgeons agree that meniscectomy is the treatment of choice for severe meniscal damage, the advantage of partial versus total meniscectomy is still debated. Although the majority of clinical cases show no clinical abnormality following meniscectomy, it has been shown that partial or total meniscectomy results in gross and microscopic degenerative changes in the articular cartilage of the femur and tibia.(49,50) While partial meniscectomy appears to lessen the amount of degenerative change,(49) it would appear that neither is a totally benign procedure.

Regeneration of the menisci following total resection has been observed in the dog.(49,59) This regenerated tissue originates from the vascular perimeniscal tissues(45) and grossly resembles fibrocartilage (Fig. 80-29). This regeneration, however, is not uniform and is not present in every case. Therefore, it would appear that, if possible, total meniscectomy should be avoided in favor of partial resection.

FIG. 80-29 (A) Normal medial meniscus and (B) regenerated meniscus 7 months following total medial meniscectomy. (Flo GL, DeYoung D: Meniscal injuries and medial meniscectomy in the canine stifle. J Am Anim Hops Assoc 14:68>689, 1978)

 

References

STIFLE KINESIOLOGY AND CRUCIATE LIGAMENT RUPTURE

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2. Arnoczky SP: The anterior cruciate ligament. Proceedings of the 98th Annual Meeting of the American Animal Hospital Association 1981, pp 321-326

3. Arnoczky SP, Lane JM, Marshall JL: Meniscal degeneration due to knee instability: An experimental study in the dog. Trans Orthop Res Soc 4:79, 1979

4. Arnoczky SP, Marshall JL: The cruciate ligaments of the canine stifle: An anatomical and functional analysis. Am J Vet Res 38:1807, 1977

5. Arnoczky P. Marshall JL: Pathomechanics of cruciate and meniscal injuries. In Bojrab MJ (ed): Pathophysiology of Small Animal Surgery, pp 590-603. Philadelphia, Lea & Febiger, 1981

6. Arnoczky SP, Rubin RM, Marshall JL: Microvasculature of the cruciate ligaments and its response to injury: An experimental study in the dog. J Bone Joint Surg 61A: 1221, 1979

7. Arnoczky SP, Tarvin GB, Marshall JL: Surgery of the stifle. Proceedings of the 46th Annual Meeting of the American Animal Hospital Association 1979, pp 387-401

8. Arnoczky SP, Tarvin GB, Marshall JL: Anterior cruciate ligament replacement using patellar tendon: An evaluation of graft revascularization in the dog. J Bone Joint Surg 64A:217, 1982

9. Arnoczky SP, Tarvin GB, Marshall JL et al: The over the-top procedure: A technique for anterior cruciate ligament substitution in the dog. J Am Anim Hops Assoc 15:283, 1979

10. Arnoczky SP, Torzilli PA, Marshall JL: Evaluation of anterior cruciate ligament repair in the dog: An analysis of the instant center of motion. J Am Anim Hops Assoc 13: 553, 1977

11. Butler HC: Teflon as a prosthetic ligament in repair of ruptured anterior cruciate ligaments. Am J Vet Res 25:55, 1964

12. Childers HE: New method for cruciate ligament repair. Mod Vet Pract 47:59, 1960

13. DeAngelis MP, Betts CW: Posterior cruciate ligament rupture. J Am Anim Hops Assoc 9:447, 1973

14. DeAngelis MP, Lau RE: A lateral retinacular imbrication technique for the surgical correction of anterior cruciate ligament rupture in the dog. J Am Vet Med Assoc 157:79, 1970

15. Dickinson CR, Nunamaker DM: Repair of ruptured anterior cruciate ligament in the dog: Experience of 101 cases using a modified fascia strip technique. J Am Vet Med Assoc 170:827, 1977

16. Dietrich HF: Repair of anterior cruciate ligament rupture using a modified lateral and medial retinacular imbrication technique. Vet Med/Small Anim Clin 69:1519, 1974

17. Dueland R: A recent technique for reconstruction of the anterior cruciate ligament. J Am Anim Hops Assoc 2: 1, 1966

18. Emery MA, Rostrup O: Repair of the anterior cruciate ligament with eight millimeter tube Teflon in dogs. Can J Surg 9:111, 1960

19. Flo GL: Modification of the lateral retinacular imbrication technique for stabilizing cruciate ligament injuries. J Am Anim Hops Assoc 11:570, 1975

20. Henderson RA, Milton JL: The tibial compression mechanism: A diagnostic aid in stifle injuries. J Am Anim Hops Assoc 14:474, 1978

21. Hohn RB, Miller JM: Surgical correction of rupture of the anterior cruciate ligament in the dog. J Am Vet Med Assoc 150: 1133, 1967

22. Hohn RB, Newton CD: Surgical repair of ligamentous structures of the stifle joint. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery. Philadelphia, Lea & Febiger, 1975

23. Hulse DA, Michaelson F. Johnson C, Abdelbaki YZ: A technique for reconstruction of the anterior cruciate ligament in the dog: Preliminary report. Vet Surg 9:135, 1980

24. Johnson FL: Use of braided nylon as a prosthetic anterior cruciate ligament of the dog. J Am Vet Med Assoc 137:646, 1980

25. Knecht CD: Evolution of surgical techniques for cruciate ligament rupture in animals. J Am Anim Hops Assoc 12:717, 1976

26. Knecht CD, Crise R. Cechner PE: Repair of avulsion of the caudal cruciate ligament in a dog using a bone screw. J Am Anim Hops Assoc 12:784, 1976

27. Leighton RL: Repair of ruptured anterior cruciate ligament with whole thickness skin. Small Anim Clin 1: 246, 1961

28. Marshall JL: Periarticular osteophytes. Clin Orthop 62:37, 1969

29. Marshall JL, Olsson S-E: Instability of the knee. J Bone Joint Surg 55A: 1561, 1971

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35. Pearson PT: Ligamentous and meniscal injuries of the stifle joint. Vet Clin North Am 1:489, 1971

36. Pearson PT, McCurnin DM, Carter JD et al: Lembert suture technique to surgically correct ruptured cruciate ligaments. J Am Anim Hops Assoc 7:1, 1971

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38. Rubin RM, Marshall JL, Wang J: Prevention of knee instability: Experimental model for prosthetic anterior cruciate ligament. Clin Orthop 113:212, 1975

39. Rudy RL: The stifle. In Archibald J (ed): Canine Surgery, 2nd ed, pp 1067-1075. Santa Barbara, American Veterinary Publications, 1974

40. Strande A: Replacement of the anterior cruciate ligament in the dog. J Small Anim Pract 7:351, 1966

41. Strande A: Repair of the Ruptured Cranial Cruciate Ligament in the Dog. Master's thesis, University of Oslo, 1967

42. Vasseur PB, Arnoczky SP: Collateral ligaments of the canine stifle joint: Anatomic and functional analysis. Am J Vet Res 42:1133, 1981

43. Vaughn LC: A study of replacement of the anterior cruciate ligament in the dog by fascia, skin, and nylon. Vet Rec 75:537, 1963

44. Zahm H: The Cruciate Ligaments of the Normal and Arthritic Knee of the Dog. Munchen, F Frank, 1964

MENISCAL INJURY

45. Arnoczky SP, Lane JM, Marshall JL et al: Meniscal degeneration due to knee instability: An experimental study in the dog. Trans Orthop Res Soc 4:79, 1979

46. Arnoczky SP, Marshall JL: Discoid meniscus in the dog: A case report. J Am Anim Hops Assoc 13:569, 1977

47. Arnoczky SP, Tarvin GB, Vasseur P: Surgery of the stifle: The menisci and collateral ligaments (Part III). Compendium on Continuing Education 2:394, 1980

48. Arnoczky SP, Warren RF, Tarvin GB et al: The microvasculature of the meniscus and its response to injury: An experimental study in the dog. Trans Orthop Res Soc 6:177, 1981

49. Cox J S. Nye C E, Schaeffer WW et al : The degenerative effect of partial and total resection of the medial meniscus in dogs' knees. Clin Orthop 109: 178, 1975

50. DeYoung DJ, Flo GL, Tvedten H: Experimental medial meniscectomy in dogs undergoing cranial cruciate ligament repair. J Am Anim Hops Assoc 16:639, 1980

51. Flo GL, DeYoung D: Meniscal injuries and medial meniscectomy in the canine stifle. J Am Anim Hops Assoc 14:683, 1978

52. Smith K: Meniscectomy. In Bojrab MJ (ed): Current Techniques in Small Animal Surgery, pp 484- 486. Philadelphia, Lea & Febiger, 1975

53. Stone EA, Betts CW, Rudy RL: Folding of the caudal horn of the medial meniscus secondary to the severance of the cranial cruciate ligament. Vet Surg 9:121, 1980