Canine Cruciate Disease, Meniscal Tears and Surgical Treatment
By Karyn K. Maxworthy (Briggs), DVM, MS,
Diplomate, American College of Veterinary Surgeons;
Atlantic Coast Veterinary Specialists
Cranial cruciate disease is one of the most prevalent orthopedic injuries in dogs today. It affects both small and large breed dogs, males and females, and young and old. Although some tears are believed to be purely traumatic in origin, the majority of cases are the result of a chronic degenerative process.
The exact cause of ligament degeneration in these patients remains a mystery. However, conformational abnormalities, endocrine disease, weight, reproductive status, and poor physical conditioning may all play a role.
Patients with cruciate disease present with a hind limb lameness that may be mild to non-weight bearing, unilateral or bilateral. Acute traumatic tears are generally severely lame initially and less lame as times go on. Chronic degeneration of the ligament may result in a waxing and waning lameness that worsens with exercise and improves with rest. Dogs with concurrent meniscal tears are typically severely lame and may have an audible click on stifle range of motion.
Diagnosis of a cruciate tear is accomplished primarily from a physical exam. Patients typically have effusion and medial buttress present in the affected stifle along with variable degrees of cranial tibial thrust and cranial drawer. Patients also typically sit with the affected limb tucked under their body and resent full extension of the stifle. Bilaterally affected dogs often throw their weight forward onto their forelimbs and have atrophied hindlimbs. They will also toe- tap from one leg to the other to avoid bearing full weight on either hind limb. Although radiographs may be used to confirm the presence of stifle effusion and medial buttress, they cannot be used to visualize the ligament. In human medicine, MRI is the gold standard for cruciate tears and meniscal injuries, but the routine use of MRI in veterinary medicine for cruciate tears has not been pursued at this time.
Treatment options for a patient with a cruciate tear can be medical or surgical. Medical management is most appropriate for animals weighing less than 25-30 pounds. Strict rest for at least 12 weeks and the use of non-steroidal anti-inflammatories for analgesia are the mainstays of medical therapy. Some small patients are able to stabilize their own stifles with fibrous tissue and regain function, however, if there is a meniscal tear present, then surgery may be necessary. For animals that do not respond to the medical therapy, then surgery should be considered.
The three most commonly performed surgical techniques for cruciate tears are the lateral suture (LS), the tibial plateau leveling osteotomy (TPLO), and the tibial tuberosity advancement (TTA). Intra-articular techniques and the fibular head transposition have been shown to be successful in stabilizing the stife joint, but are much less commonly performed due to decreased success rates and technical difficulty. The lateral suture technique has been the mainstay of stifle stabilization for several decades. This technique relies on a suture passed from the lateral fabella through the tibial tuberosity that is tightened to eliminate cranial drawer and cranial tibial thrust throughout range of motion. This technique is minimally invasive and less expensive when compared to the TPLO and the TTA. The post-operative complications encountered are few, but persistent instability causing poor function of the limb can be frustrating.
The TPLO was first described in the early 1990s by Dr. Slocum and quickly became one of the most popular stabilization techniques performed. The TPLO stabilizes the joint by rotating the weight-bearing portion of the tibial plateau to reduce the tibial plateau angle (TPA) to about 5o (normal dogs have a TPA of 22o - 24o). By reducing this angle, cranial tibial thrust in the weight-bearing phase of gait is converted to caudal tibial thrust, and there is increased stress in the caudal cruciate ligament. Therefore, the stifle is stable while the animal is bearing weight. Although the technique is more invasive and more expensive than the lateral suture, many surgeons feel that large dogs perform better after a TPLO when compared to other techniques. This belief has not been proven in the literature, however. There has been only one report of a comparison study done by Dr. Conzemius in 2005 showing no difference between TPLO and lateral suture treated dogs six months post-operatively as demonstrated with the use of force plate analysis. Also, post-operative complications can be more severe with techniques such as the TPLO including tibial fracture, implant complications, infection, meniscal tears, gait abnormalities, patellar tendonitis, etc. Despite the complications, Dr. Priddy reported that 93% of owners were satisfied with the outcome following TPLO.
The TTA procedure is very similar to the TPLO as it also involves an osteotomy of the tibia and converts cranial tibial thrust in the weight-bearing phase of gait to caudal tibial thrust, thereby stabilizing the joint. Although this procedure is newer than the TPLO, several reports are now in the literature showing its biomechanical effectiveness. Drs. Lafaver and Boudrieau have also reported on TTA complications and found 12% of cases had major and 19% had minor complications. The complications encountered were the same as seen for the TPLO. Despite the complications, they also found positive results with 97% of cases showing mild or no lameness at the time of healing.
Although many surgeons have personal preferences as to which stabilization procedure they recommend to clients, there are no studies in the literature documenting one procedure's superiority to another when considering the lateral suture, TPLO, and TTA. Despite the lack of impartial data, many surgeons believe that larger dogs perform better after an osteotomy procedure than after a lateral suture. Due to the paucity of comparison studies, making a decision as to which procedure is best for an individual patient requires a thorough dialogue between the surgeon and the client.
Meniscal tears are very common in dogs with concurrent cranial cruciate tears and virtually never occur in the cruciate-competent stifle. The medial meniscus is most frequently affected due to its firm attachments to the tibial plateau. The lateral meniscus, by comparison, is freely moveable at the caudal aspect as it is attached to the femoral condyle and not the tibial plateau. This allows the lateral meniscus to move with the femoral condyle if cranial tibial thrust is present. The medial meniscus cannot alter its position, and therefore is crushed at the caudal aspect by the femoral condyle when cranial tibial thrust occurs. Because meniscal tears are known to be very painful from human accounts, it is important to determine the status of the medial meniscus when performing a cruciate stabilization procedure.
To evaluate the medial meniscus, a parapatellar arthrotomy or stifle arthroscopy must be performed. The meniscus can tear in a number of different configurations, and any torn portion should be removed completely. This is because the healing potential for the menisci is extremely limited as only the abaxial rim has a blood supply. The axial portions of the menisci rely on diffusion of nutrients from the synovial fluid, and therefore are not capable of healing effectively. If a tear is present, either a complete, partial, or hemimeniscectomy (removal of the caudal pole) can be performed. It has been shown that complete meniscectomies lead to increased osteoarthritis when compared to partial meniscectomies.
For the TPLO procedure, a meniscal release is performed if the medial meniscus is healthy and intact at the time of surgery. A meniscal release is designed to give the caudal pole of the medial meniscus increased mobility so that it is not injured by any remaining instability throughout the stifle's range of motion. The meniscus is released by either transecting the caudal menisco-tibial ligament, or by transecting the meniscus midbody just caudal to the medial collateral ligament. There is tremendous debate as to whether a meniscal release is warranted for the osteotomy procedures. Inevitably, any distortion of meniscal anatomy will lead to the progression of osteoarthritis.
However, post-stabilization meniscal tears have been well-documented in the veterinary literature and can be very frustrating for both surgeons and clients. Many surgeons feel that the meniscal release decreases the rate of post-stabilization meniscal tears and the need for second surgical procedures.
Cranial cruciate and concurrent meniscal tears are very common orthopedic injuries in a dog. Although numerous treatment modalities are available to the veterinary practitioner, controversy continues as to which therapy is superior. Many factors -- such as patient size, age, activity level, and owner finances -- may influence the decision-making process. A thorough discussion about the pros and cons to each procedure is indicated so that the client can make an informed decision for their pet.