Cranial Cruciate Ligament Rupture

 

Signalment

Breeds – Any breed, but Labrador retrievers, Rottweilers, Bernese Mountain dogs, St. Bernards, and other large and giant breeds seem to be particularly affected. Cruciate ligament rupture occurs in small breed dogs, but dogs should be carefully evaluated for concurrent patella luxation.

 

Gender – Spayed females may be predisposed

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Age – Middle-aged to older dogs (4 to 8 years of age) are more commonly affected.

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Etiology - While acute rupture of the cranial cruciate ligament may occur as a result of trauma, nearly all cases of cranial cruciate ligament rupture (CCLR) occur as a result of a slow degenerative process of the fibers of the ligament. Loss of CCL support invariably leads to progressive OA.  Rupture of the cranial cruciate ligament results in gross instability of the stifle. Alternatively, the ligament may sustain a partial rupture, causing less obvious instability and lameness. In both cases, degenerative joint changes are initiated at the time of the rupture, and progress with time. Joint instability invariably leads to progressive OA with deterioration of limb function. Based on recent studies, there may be a genetic component to CCLR in some breeds. Bilateral cruciate ligament disease is quite common. 

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History

Dogs may have a progressive pelvic limb lameness or a sudden nonweightbearing lameness. The lameness may improve gradually over the first few weeks, and then worsen again. Alternatively, the ligament may sustain a partial rupture, causing less obvious instability and lameness. Dogs have reduced activity, difficulty negotiating stairs, and may not sit squarely and symmetrically. 

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Clinical Findings

Dogs typically have lameness, ranging from barely perceptible to nonweight-bearing lame. The joint is assessed for swelling by palpating medial and lateral to the patellar ligament.  Normally, the edges of the ligament can be distinctly felt, but with joint effusion, the patellar ligament is less distinct and fluid may be palpable.  The femoral condyles and trochlear ridges are palpated for osteophytes or joint capsule thickening.  Thickening of the medial aspect of the distal femur is often present in dogs with chronic rupture of the cranial cruciate ligament (medial buttress).  The stifle is flexed and extended to evaluate for crepitus, clicking, or snapping, which might indicate osteoarthritis or a damaged meniscus.  Dogs with complete or partial cranial cruciate ligament rupture often have marked pain with full stifle extension.

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The most common method of assessing for cranial cruciate ligament rupture is the cranial drawer test.  One index finger is placed on the tibial tuberosity and the soft tissues are stretched caudally with the thumb until the head of the fibula is reached.  The other index finger is placed on the patella and the soft tissues are stretched with the thumb until the lateral fabella is palpated.  Now place the stifle in mild flexion and try to move the tibia cranially and caudally.  The examiner should avoid internally rotating the limb while performing the drawer maneuver.  Drawer motion should be assessed through a range of motion. In some cases of partial cranial cruciate ligament rupture there may be some drawer motion in flexion but not extension.  Sedation may be necessary in some tense patients.  

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An indirect method of evaluating the cranial cruciate ligament is the tibial compression test.  The stifle is flexed to a standing angle.  One hand is placed on the stifle with the forefinger resting on the tibial tuberosity.  The tarsus is slowly flexed with the other hand, while keeping the stifle at a fixed angle.  This causes tension in the gastrocnemius muscle and common calcaneal tendon which compresses the femur and tibia.  In the absence of the cranial cruciate ligament, cranial movement of the tibial tuberosity in relation to the distal femur is detected.

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Diagnostics

Cranial cruciate ligament rupture is a diagnosis by physical examination. MRI may be performed in cases of partial rupture of the cruciate ligament, but this is expensive and there is generally a high index of suspicion based on physical exam.  Radiographs are typically made to assess the degree of osteoarthritis that may be present. Osteophytes may be seen on the distal pole of the patella, on the tibia near the insertion of the cranial cruciate ligament, the medial and lateral epicondyles, and the fabella. Effusion of the stifle joint is nearly always present as assessed by evaluating a lateral radiograph for compression of the fat pad in the cranial portion of the joint, and bulging of the joint capsule in the caudal portion of the joint. If an extracapsular procedure is being considered, evaluation for the presence and position of the fabella is performed. When considering biomechanical-altering procedures such as tibial plateau leveling osteotomy or tibial tuberosity transposition, the tibial plateau angle are measured from a lateral view.  Finally, the joint should be evaluated for neoplasia.  Approximately 1 in 200 patients with lameness localized to the stifle joint may have neoplasia, including osteosarcoma of the distal femur or proximal tibia, or histiocytic sarcoma involving the joint itself. 

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Treatment Options

Surgical stabilization is recommended for a successful outcome.  Inadequate surgical and postoperative treatment may result in joint stiffness, muscle atrophy, lameness, and poor function.  Proper surgical intervention and the appropriate use of physical rehabilitation techniques in combination with pharmaceutical agents are necessary to achieve an optimal outcome.  

        

In some cases, such as the concurrent presence of terminal disease such as neoplasia, or severe organ dysfunction that would endanger the patient's life with anesthesia, conservative treatment may be opted. It is important to realize that satisfactory function will occur in about 20% of dogs. In small dogs (less than 15 kg), conservative therapy may suffice if surgery is not an option, although surgical treatment is still the preferred route to reduce the atrophic and degenerative changes that invariably occur with conservative treatment.  In larger dogs, some form of stifle stabilization is nearly always advocated to prevent or minimize the progression of OA.  

 

To date, over 50 different techniques have been devised to treat CCLR.  These techniques range from simple forms of extracapsular stabilization using wire or suture material, to sophisticated arthroscopic prosthetic ligament replacement.  In addition to the stabilization procedure, it is important to debride loose and torn ligament remnants and to inspect and debride damaged portions of the menisci, especially the caudal horn of the medial meniscus, which is frequently damaged in dogs with CCLR.  The method of joint exploration may have an effect on early postoperative recovery.  An arthrotomy carries significant morbidity, while arthroscopic evaluation and joint debridement, although more difficult and time consuming, results in less pain and swelling, and earlier return to limb use. 

 

Extracapsular stabilization

In this form of stabilization, nylon suture or stainless steel suture material is used to provide extracapsular (outside the joint capsule) support, mimicking the support provided by the intact CCL.  Most commonly, the suture is passed around the lateral (and sometimes a separate suture around the medial) fabella (sesamoid bone located in the origin of the gastrocnemius muscle) and through a tunnel drilled into the proximal tibial tuberosity.  This procedure minimizes cranial drawer and provides immediate stabilization of the stifle, allowing early rehabilitation to be initiated.  At some point, the prosthetic material may fatigue and break.  However, the periarticular fibrosis that develops over 8 to 10 weeks provides the ultimate stabilization of the stifle.  Nevertheless, it is common for some degree of cranial drawer motion to be present weeks to months after surgery.  Rehabilitation after surgery seems to reduce the amount of postoperative drawer motion and may result in a more stable joint.

            Another form of extracapsular stabilization is the tightrope procedure.  With this procedure, bone tunnels are drilled to mimic the isometric points of the cruciate ligament on the lateral side during joint flexion and extension.  Fiber tape is used with a toggle rod and button to stabilize the stifle.  The advantage of this technique over traditional extracapsular techniques is that the fiber tape maintains tension throughout a range of motion because the tape is placed in a more isometric position.  The procedure has tested well in biomechanical tests and early clinical results are good.  The repair provides immediate stability to the stifle joint, but over time, some drawer motion may return.

            Physical rehabilitation starts the day of surgery with cryotherapy, NSAIDs, and gentle passive range of motion (PROM).  Controlled leash walks are started within 24 hours and active use of the limb is encouraged.  Treadmill walking may be useful to encourage weight-bearing, and aquatic therapy may be started approximately one week post-operatively if the incision is sealed and there is no opening of the wound edges or drainage or discharge from the incision.  PROM is continued with an emphasis on regaining preoperative levels of stifle joint extension by 10 days after surgery.  Rear limb strengthening can be facilitated by stair climbing, uphill walking, or pulling a cart.  Jumping up on the hind limbs is prevented for the first 10 to 12 weeks to prevent damage to the repair.

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Tibial Plateau Leveling Osteotomy (TPLO)

This procedure uses a completely different concept to provide stability to the stifle joint.  The main concept behind the previously described procedures is to limit cranial drawer motion by physically restraining the tibia from shifting cranially in relation to the femur during weight-bearing or nonweight-bearing activities.  The TPLO is based on the principle that cranial tibial thrust during weight-bearing is prevented using a combination of altered biomechanical forces and active muscle contraction acting on the stifle during weight-bearing to stabilize the joint.  Clinical experience and a growing number of studies have shown that this procedure gives the most consistent and best results regarding clinical function and slowing the progression of osteoarthritis. 

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            The principles of this procedure are most easily understood if one considers that in the normal stifle, the weight-bearing surface of the tibial plateau slopes caudally.  With CCLR, the femoral condyle is not restrained by the CCL and the femoral condyles roll down this slope during weight-bearing, resulting in a net cranial displacement of the tibia in relation to the femur.  This overall concept is similar to performing a tibial compression test, in which forces and muscle tension acting on the stifle result in cranial displacement of the tibia in the CCL-deficient stifle.  With the TPLO, an osteotomy of the proximal tibia is performed, allowing the tibial plateau to be rotated to nearly level position.  The osteotomy is then stabilized using screws and a specially designed bone plate.  This reduces the shear forces acting at the articular surfaces of the femur and tibia, resulting in more compressive forces and eliminating the cranial tibial thrust during weight-bearing.  The periarticular muscles provide additional stability to the stifle during weight-bearing.

  

         Cryotherapy, NSAIDs, and PROM exercises, along with limited activity in the form of progressively longer leash walks, are provided in the initial postoperative period.  As healing of the osteotomy site progresses, a gradually increasing protocol of limb use is prescribed.  It is important to realize that in addition to healing joint capsule and altering stresses on the cartilage and bone of the joint, that the osteotomy has adequate time to heal to prevent complications related to bone healing and implant failure.  In this regard, aquatic therapy may be particularly useful to reduce weight-bearing forces.  

 

         The postoperative complications associated with this procedure are primarily related to the altered biomechanics of the stifle.  In particular, patellar ligament desmitis is very common during the first month.  Clinically, patients may demonstrate more lameness during the postoperative period than is normally expected if patient activity is not adequately restricted. The patella ligament is wider, and there is pain on palpation of the ligament, especially at its insertion to the tibial crest.  Also associated with the altered biomechanical stresses placed on the joint, is the occurrence of avulsion of a portion of the tibial crest in some patients.  Postoperative rehabilitation protocols must consider these possible complications. Fortunately, the problems are usually self-limiting as tissue remodeling and healing progress.  Preventive strategies, centered on preventing excessive stresses of the patellar ligament on the tibial crest, may be useful in the early postoperative period. Specifically, preventing excessive flexion of the stifle while weight-bearing should reduce the tensile forces at the ligament insertion point.  Preventing jumping, running, stair climbing, and walking while crouching should help to keep the quadriceps muscle-patellar ligament unit in a relatively shortened position, reducing the tensile forces on the tibial crest and patellar ligament.  If patellar ligament desmitis occurs despite these preventive measures, treatment in the form of severely restricting exercise, cryotherapy, and NSAIDs, should help to resolve the problem before becoming more serious.  A more gradual increase in activity level should be instituted after the tissues have healed adequately to resume activity. 

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CORA-Based Leveling Osteotomy (CBLO)  

            The concept behind this procedure is similar to the TPLO, but the tibial osteotomy is further distally away from the joint is the circular cut is directed in the opposite direction. A special compression screw along with a specialized bone plate and screws secure the position of the bones after rotation.  Although some have described advantages of this technique over TPLO, there is insufficient evidence to suggest better clinical outcomes than those achieved with TPLO at this time. One advantage of the CBLO is in dogs with open growth plates because the level of the osteotomy avoids the growth plate.       

 

Tibial Tuberosity Advancement (TTA)

This procedure is similar in principle to the TPLO, but it accomplishes the goal of providing dynamic stability to the stifle joint by advancing the tibial tuberosity as opposed to rotating the tibial plateau.  The end result is that contraction of the quadriceps muscle causes compression of the joint rather than shearing forces that result in cranial tibial thrust.  

 

           The procedure is performed by performing an osteotomy of the tibial tuberosity.  The tuberosity is advanced to a point that eliminates cranial tibial thrust.  The osteotomy is held in place with a specially designed plate and cage or material in the shape of a wedge which maintains the proper amount of advancement.  Bone graft is used to fill the defect created by the advancement.

 

            Postoperatively, it is important to allow healing of the osteotomy, which generally takes 4 to 8 weeks.  During that time, control of pain and inflammation are important.  In addition, excessive activity is avoided to allow proper healing.

 

           Proponents of the technique indicate that surgery time is shorter than the TPLO and the procedure is less invasive, potentially resulting in a lowered incidence of postoperative infections.  In addition, there is generally no or little patella ligament desmitis, and because there is no increased tension of the quadriceps mechanism, there is no patella or tibial crest fracture, and patella-femoral chondromalacia is minimal.  Compared to the TPLO, resorts suggest that the incidence of post-operative meniscal tears is greater with TTA.

 

Intracapsular stabilization methods

These procedures have fallen out of favor, but use fascial strips, a portion of the patellar ligament, or prosthetic materials placed in an intraarticular fashion via arthrotomy or arthroscopy to mimic the anatomic path of the original CCL and allow more normal stifle joint kinematics.  Most procedures using a graft leave one end of the graft attached to the tibial crest and have the free end of the tissue pass through the stifle joint, going caudally and proximally through the joint capsule, and then are secured to the lateral femoral condyle.  Other procedures have the free end of the graft pass under the intermeniscal ligament prior to traversing caudally and proximally through the joint.  If the placement is not isometric, stretching and tearing of the implant may occur.  In addition, biological tissues undergo a prolonged period of weakness until the tissue revascularizes and gains additional strength.  This process may take months, and the tissue may not regain sufficient strength to function in the same fashion as a normal CCL.  To combat this process, some surgeons also use an extracapsular fabella-tibial suture to augment the repair and reduce the stress on the graft.  To date, prosthetic material used in veterinary medicine has been universally unsuccessful in providing permanent stability to the stifle.  Invariably, the material degenerates, often resulting in chronic intra-articular inflammation.

 

             Postoperative physical rehabilitation includes reducing pain and the inflammatory response through the use of NSAIDs and cryotherapy.  Depending on the material used, the rehabilitation efforts must follow changes in tissue strength.  For example, in cases with an autograft or allograft of fascia, rehabilitation efforts must conform to changes in the strength of the implant over a period of time.  In particular, autografts and allografts are generally strong when initially put in place, but when put under tension, they stretch.  Also, the tissue becomes much weaker over the next 2 to 20 weeks while revascularization and incorporation occur.  If graft incorporation is augmented with an extracapsular suture, a rehabilitation program similar to that for extracapsular repair may be initiated, although attention to controlling inflammation is particularly important to prevent a hostile environment for the graft.  Ultimate tissue strength is only achieved following bio-integration of the graft.