Surgical management of cranial cruciate ligament disease (Proceedings)

There have been numerous developments in the field of canine cranial cruciate ligament disease. This lecture will summarize the current knowledge and benefits, both short-term and long term, of extracapsular, intracapsular, and TPLO repairs. The question of meniscal disease will also be discussed.

Cranial cruciate ligament disease (CCL) in dogs is not only common but also very costly for the owner. It has been estimated that approximately $1.32 billion is spent annually by dog owners for the treatment of this disease with an average cost per stifle surgically treated of $898 to $1,840. Since CCL disease affects so many dogs, an up to date knowledge base is vital for every practitioner.

There are a number of risk factors for dogs developing CCL disease and dogs at risk are better served by educating the client before rupture of the ligament has occurred. Once degenerative joint disease has begun following rupture of the ligament; it is virtually impossible to stop, although slowing the progression of osteoarthritis is an attainable goal. Many risk factors have been identified including an increased incidence in spayed and neutered dogs, increasing age of the dog, overweight dogs, and dogs fed a premium or therapeutic diet. Breeds at risk of CCL disease in dogs older than 6 years of age include the Boxer, Labrador retriever, Rottweiler, Siberian Husky, and Bichon Frise. If the dog is less that 2 years of age at presentation for CCL disease, the risk factors differ from those listed above. In this younger group, the breeds most commonly affected are the Mastiff, Newfoundland, Akita, St. Bernard, Rottweiler, Labrador retriever, and American Staffordshire terrier. The incidence in these breeds increases if the dog is overweight, spayed, or neutered. Females, especially those ovariectomized, have an increased incidence of CCL disease regardless of their age. This is also true for humans affected with CCL disease, but the cause in either species has not yet been identified. Obesity presumably contributes to the disease due to the increased forces placed on the ligament from excessive body weight, but a breed predisposition exists regardless of the dog's body condition score. A recessive mode of inheritance has been identified in the Newfoundland. Expression of CCL disease in this breed would require two copies of the mutant allele and an environment for expression of the disease as well. Therefore, only 51% of Newfoundlands with two mutant alleles for the gene actually develop a ruptured cruciate ligament. If we control environmental factors such as body condition score, housing conditions, neutering status, diet, etcetera, we can prevent rupture in dogs; even those such as the Newfie with a genetic predisposition.

Many dogs with CCL disease also have other orthopedic conditions, which must be considered when discussing treatment with owners. Degenerative joint disease is present in the coxofemoral joints of 32% of dogs with CCL disease and 43% of dogs with bilateral CCL disease also have hip osteoarthritis. Many theorize that excessive strain is placed on the CCL due to an abnormal gait secondary to the inflammation and pain associated with hip osteoarthritis.

The function of the CCL is important since the instability that results after its rupture is directly a result of the loss of CCL function. The CCL prevents cranial translocation of the tibia in relation to the femur, prevents hyperextension of the stifle, and prevents excessive internal rotation of the tibia. Rupture of the CCL was once thought to occur solely as an acute traumatic event such as a hyperextension injury during strenuous activity. More cases are now believed to be due to a chronic progressive degeneration of fibroblasts in the ligament and fibrillation with tearing of the fibers. The remaining fibers are overloaded, loose their crimp, elongate and finally fail. The initiating cause is unknown but may be due to poor blood supply, lack of sex hormones or other factors.

The diagnosis of cruciate ligament disease is hampered by the fact that signs of radiographic osteoarthritis do not necessarily correlate with clinical function of the stifle joint. Physical examination may not indicate early disease and partial tears. Nuclear scintigraphy and MRI are more sensitive detectors of early disease, however they are not widely available. Therefore, dogs with several risk factors for CCL disease and intermittent stifle lameness warrant further investigation including examination of the stifle joint under sedation or general anesthesia and even arthroscopy.

Treatment of CCL disease is a controversial topic amongst many veterinarians. Conservative management is an acceptable technique for dogs and cats weighing less than 15 kg. Conservative treatment involves at least 2 months of cage rest and passive range of motion exercises, with or without the use of chondroprotective agents. Many cats require longer periods of confinement and the length of time depends on the findings of serial cranial drawer examinations.

Chondroprotective agents are numerous but hyaluronic acid in particular has received much interest. Hyaluronan is a component or intra-articular cartilage and synovial fluid. When administered via intra-articular injection, it reportedly decreases inflammation by down-regulating cytokine production. While hyaluronan may decrease inflammation and cartilage deterioration, it does not prevent the progression of osteoarthritis in CCL deficient stifle joints of dogs. Glycosaminoglycans and chondroitin sulfate are two other commonly employed chondroprotective agents. In humans the use of chondroitin has not proven to be beneficial in reducing joint pain. Glycosaminoglycans and chondroitin sulfate may not reduce pain but have been shown to decrease matrix metalloproteinases in arthritic joints which will slow the progression of joint disease.

Surgical treatment for CCL disease can be divided into three basic groups: extracapsular repair, intracapsular repair, and tibial alteration. These surgeries all involve examination of the joint to determine the degree of inflammation and CCL damage as well as to assess the menisci. Examination of the joint can be performed via arthroscopy or arthrotomy. Arthrotomy is more invasive but less costly than the training and time-consuming arthroscopic procedure. Arthroscopy, however, results in increased limb use and mobility in the first 8 weeks post-operatively resulting in a potentially improved long-term outcome. Progression of osteoarthritis is decreased with a limited arthrotomy versus a full parapatellar arthrotomy and therefore limited approaches to the joint should be employed whenever possible.

Extracapsular suture repair (ECS) has been used for many years in the treatment of CCL disease. This method of treatment does not require expensive instrumentation or specialized training for it's use and is performed widely by many veterinarians. Placement of the suture in a fabello-tibial orientation results in the least displacement with cranial tibial translation and therefore results in the most stable repair. The type of suture used should be non-reactive, maintain strength following sterilization, and be resistant to bacterial colonization. Monofilament nylon leader material or mason leader line has the best properties for this application and is most commonly used Crimping the suture with clamps rather than tying the suture into knots appears to provide greater stability to the repair post-operatively since there is less slipping of the suture through clamps while knots tend to lengthen over time. Complications (overall 10 to 21% of cases) with the ECS repair include infection in 25 to 80% of cases, continued joint instability, and progression of osteoarthritis.

Intracapsular repair (IC) involves placement of a prosthetic where the original CCL was in order to take its place and provide the joint with a new ligament as close to replicating the original CCL as possible. Many tissues can be used including the tensor fascia, patella tendon, and hamstrings fascia Complications of the intracapsular techniques include slipping or tearing of the graft and prolonged lameness following surgical repair. With the hamstring technique the dogs remained significantly lame at 12 weeks post operatively and often take up to 52 weeks for the post-operative lameness to resolve. The major benefit to intracapsular techniques is the prevention of progression of osteoarthritis in the stifle joint; something which the other techniques cannot prevent.21 Methods to improve this technique are likely to improve the outcome in the future. Injection of tricalciuim phosphate into the bone tunnels created for the prosthetic can speed healing, decrease slippage and prevent tearing of the graft; however, this technique has not been performed in clinical cases.

Tibial alteration surgeries include the tibial plateau leveling osteotomy (TPLO) and tibial tuberosity advancement (TTA). TPLO has gained wide acceptance in recent years due to the excellent outcome in 73% or more cases, decreased complication rate, and return to normal weight-bearing in 18 weeks. Potential complications include tibial fracture, osteomyelitis, fibular neck fracture, meniscal damage, implant failure, hemorrhage from the popliteal artery, and osteosarcoma. Meniscal damage may occur following TPLO surgery since the procedure does not prevent cranial tibial translation or internal rotation of the femur when the patient is non-weight bearing. Many surgeons therefore, perform a meniscal release to prevent meniscal damage after surgery. In a recent report, however, meniscal tears occurred as frequently following TPLO surgery whether the meniscus was released or not (5-7% of cases). The incidence of meniscal tears is 4 times as common if an arthrotomy is performed and the meniscus was not released at the time of surgery compared to a decreased incidence with arthroscopy. Therefore, if arthroscopy is performed meniscal release is not necessary, as it does not decrease the incidence of subsequent tears. On the other hand, if an arthrotomy is performed, the meniscus should be released to prevent a subsequent tear Arthroscopy performed in conjunction with a TPLO may negate any need for meniscal release to be perfomed and preservation of the meniscus can reduce progression of osteoarthritis. When the meniscus is damaged however, the torn portion must be removed since it is unlikely to heal and will be a source of pain and inflammation.

Tibial tuberosity advancement is performed to advance the insertion of the patellar tendon perpendicular to the tibial plateau in order to convert cranial tibial thrust into caudal tibial thrust. Like TPLO, TTA does not prevent cranial tibial translation or internal rotation of the femur when non-weight bearing. TTA has been reported to have an excellent outcome in 90% or more of cases and to allow early weight bearing of the operated limb. Complications of the procedure include infection; implant failure, tibial crest displacement, and medial meniscal tears. Unfortunately, 67% of cases have progression of osteoarthritis following surgery. No study has yet looked at the need to perform medial menisectomy with TTA although one study reports a 5% incidence of medial meniscal tears following surgery (no meniscal release was performed at surgery).

All surgical repairs except intracapsular repair relies on formation of periarticular scar tissue to eventually stabilize the joint so that there is no cranial tibial translocation at any time whether weight bearing or not. Comparison of surgical techniques has revealed that no repair is superior to others in terms of lameness 2 to 6 months after surgery. Only 11 to 15% of dogs undergoing extracapsular, intracapsular or TPLO repair had normal peak vertical force and vertical impulse on the operated limb at 2 to 6 months post-operatively. Most patients improve, but many remain with lameness following heavy exercise.

Extracapsular, TPLO and TTA surgeries all have radiographic progression of osteoarthritis long term, however, progression of degenerative joint disease may be less with intracapsular repairs. Intracapsular repairs have the down side of continued lameness for up to one year post-operatively, even if there is no progression of osteoarthritis, unlike the other procedures where limb use improves within a few months of surgery.

Meniscal damage commonly occurs secondary to the instability that develops in the stifle joint following CCL rupture. At least 58% of CCL disease cases have medial meniscal damage and the incidence of tears increases as the degree of CCL rupture increases so that many complete CCL ruptures have meniscal tears as well. The most common medial meniscal damage is a bucket handle tear or radial tears of the caudal pole of the meniscus. Diagnosis of meniscal damage pre-operatively is difficult since there is no correlation with radiographic changes in the stifle and even force plate analysis has only a 52% sensitivity and 72% accuracy for detecting meniscal tears. Ultrasound detection has 90% accuracy for detection of meniscal damage, especially if the dog is greater than 21 kg in size and may be a better option for diagnosing meniscal damage pre-operatively. Treatment of meniscal damage is aimed at removing the damaged portion since leaving the peripheral rim of the meniscus protects articular cartilage. Removing the caudal half of the meniscus results in progression of osteoarthritis just as removing the entire meniscus would, but is sometimes required with severely damaged medial menisci. Replacement of the caudal pole of the meniscus with small intestinal submucosa has been investigated experimentally with some success especially if the implant has been stabilized with a tibial tunnel.

Lateral meniscal tears occur frequently with CCL disease but they are mostly small radial tears that do not affect outcome following surgical treatment. Isolated lateral meniscal tears can occur with or without CCL disease and is seen infrequently in Boxers. The cause of the tears is unknown but treatment with TPLO surgery may not improve the lameness. Treatment with immunosuppressive therapy for immune-mediated joint disease has been attempted but the outcome has not been reported.

Physical rehabilitation has become popular for the treatment of CCL disease and can improve outcome if combined with appropriate surgical management. Dogs with ECS repair and complete medial menisectomy that received rehabilitation were normally weight-bearing by 6 months post-operatively, whereas those that did not receive rehabilitation continued to be lame. Rehabilitation can include exercises in an underwater treadmill and/or exercises performed at home by the client with veterinary supervision.

In conclusion, no one surgical procedure is currently proven as the best technique for all dogs affected with CCL disease. Early intervention before onset of osteoarthritis is still the best method for preventing progression of degenerative joint disease as the patient ages. Rehabilitation and possibly supplementation with chondroprotectives along with surgical stabilization are the most successful programs in the treatment of this disease and it is recommended that veterinarians consider all methods.

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