Cranial Cruciate Ligament Rupture and Repair
Rupture of the cranial cruciate ligament in the knee joint is a very common injury which causes significant joint instability, lameness and if left untreated leads to crippling arthritis. There are several options for surgical repair and at The Vet Centre we keep ourselves up to date with the most recent repair techniques. We were the first veterinary practice in Nelson/Marlborough to offer the very successful technique of triple tibial osteotomy (TTO).
What is the cruciate ligament?
There are two cruciate ligaments within the knee joint, a cranial ligament and a caudal ligament. Together these ligaments stabilise the knee joint, preventing backwards and forwards motion of the two leg bones (femur and tibia) relative to each other at the knee joint. If one of these ligaments ruptures the knee joint becomes unstable and the bones rub backwards and forwards against each other causing pain, lameness and erosion of the cartilage and other structures within the knee joint. The cranial cruciate ligament (CCL) is the more important of the two ligaments as it bears the most load during normal activity. It is the CCL that ruptures most commonly.
There are several reasons why the CCL might rupture. Young athletic dogs can suddenly rupture the ligament if they take a bad step or make a bad turn during play. This causes a sudden lameness. We often see this injury in active working dogs.
Another situation is in older large breed dogs, especially those that are overweight. These dogs may have chronically weakened ligaments and the ligaments may progressively stretch over time. In this situation the ligament may partially tear causing a chronic waxing and waning lameness. This partially torn ligament may then suddenly rupture at any time even if the dog is not doing anything particularly active. As the ligaments in both knees are likely to be chronically weakened it is common in this situation for both knees to have a cruciate injury during the animal’s life.
There is a genetic component in that certain breeds are more likely to develop chronically weakened cruciate ligaments. Those breeds at higher risk include: Neopolitan mastiff, Newfoundland, Akita, St. Bernard, Rottweiler, Chesapeake Bay retriever, Staffordshire bull terrier.
Diagnosis of CCL rupture
If the ligament has completely ruptured/torn it is possible to feel the backwards and forwards motion of the tibia relative to the femur at the knee joint. If there is a partial tear then diagnosis can be more difficult. Usually sedation is needed to accurately assess the knee joint. Often with chronic cruciate injuries or partial tears there will be thickening of the knee joint and pain when manipulating the knee. Xray’s of the knee may show an increase in the volume of joint fluid and arthritic changes within and around the joint. A combination of palpation of the joint and taking Xray’s usually allows accurate diagnosis of cruciate injury though sometimes exploratory surgery of the knee joint is needed to confirm the diagnosis.
There have been many different techniques used over the years for CCL repair. Some are now no longer used and others have been extensively modified in the search for the ideal repair method. The aim of cruciate repair is to regain mobility with little or no ongoing lameness and to offset the time of development of arthritis. The best repair method will depend on the situation of each individual animal. Traditional methods involve replacement of the ligament with surgical implants such as pieces of nylon or strips of connective tissue. Newer techniques involve surgically altering the whole biomechanics of the knee joint so that a ligament is no longer needed.
This is our simplest repair method but is best suited for small breed dogs (<15kg) and cats. It is also our cheapest repair method and so may also be an option for the money conscious owner. It is not however recommended for large breed dogs (>25kg). This technique involves replacing the CCL with a piece of ligafiba, passed around a small bone behind the knee and through a tunnel drilled through the tibia. LigaFiba is a new, braided, ultra high molecular weight polyethylene which is 2.5 times as strong as nylon and being flexible is much less likely to break than nylon. The position of the ligafiba approximately mimics the position of the CCL. Possible complications of this technique include the premature snapping of the implant, before scar tissue has grown along it, or the loosening of the knot used to tie it. At The Vet Centre we have minimised these problems by using very strong ligafiba for the implant and we use a special non-slip ‘locking loop’ knot to secure it.
This is similar to the above technique but has modifications that make it a much more successful technique. The first modification is the use of LigaFiba. LigaFiba is a new, braided, ultra high molecular weight polyethylene which is 2.5 times as strong as nylon and being flexible is much less likely to break than nylon. The second modification is in the positioning
of the LigaFiba to more accurately mimic the position of CCL. The isometric points are used for LigaFiba placement so that the tension of the LigaFiba remains constant throughout the full range of motion of the knee. The use of the isometric points is made possible by the use of a special toggle to anchor the LigaFiba on the inside of the knee through a bone tunnel in the femur. This more accurately mimics the path of the CCL than the above technique. Also the use of toggles makes the stability of the repair much less reliant on the nature of the knot used so knot loosening is much less of a problem. This technique can be used in all sized patients.
This technique is a relatively new approach to CCL injury and is generally only used in larger breed dogs. It does not repair the ligament as such but alters the whole biomechanics of the knee joint so that a CCL is no longer needed. The knee joint is stabilised by the action of actively contracting muscles. The purpose of developing this technique was to improve the success rate in treating cruciate rupture in large breed dogs where failure of nylon implants is more likely than in smaller animals.
There are a variety of techniques available to alter knee joint mechanics and the TTO combines two of the most successful techniques, the TPLO (tibial plateau levelling osteotomy) and TTA (tibial tuberosity advancement). In the normal knee joint the slope on the top surface of the tibia results in a lot of load bearing force being exerted onto the CCL. If the ligament is ruptured this force causes the tibia to move forwards. If the top surface of the tibia is made level then there is no force to move the tibia forwards and so the knee joint remains stable despite having no CCL.
To achieve a level tibial plateau three cuts are made in the tibia and a wedge of bone is removed. The cut ends of bone are compressed together which alters the angle of the top of the tibia and at the same time moves the front edge of the tibia further forwards. The bone is then held in its new position with a special ‘T’ shaped bone plate. This technique is technically difficult and requires investment in special instruments to make accurate cuts in the bone. The Vet Centre has invested in the necessary equipment and expertise and has been successfully performing this surgery since 2006.
Excellent results have been achieved with this technique, with more rapid recovery times, less progression of arthritis and return to athletic function even in large breed dogs.
What to expect after surgery
Rehabilitation following surgery involves a 3 month period of restricted activity with no running or jumping. Controlled swimming and lead walking are permitted. It may take 2-3 three weeks following surgical correction with nylon implant or LigaFiba before there is significant weight bearing whereas it may only take 2-3 days following TTO surgery. Stitches are removed 2 weeks after surgery.
Apart from post-surgical infection or inflammation which can happen with any surgical wound, the most likely complication is premature breakage of the nylon implant or loosening of the knot. The risk of this is much reduced if LigaFiba is used and is not a problem associated with TTO surgery. With TTO surgery there is a small risk that the screws holding the plate on may loosen and require further surgery to tighten. There is also a small risk of bone infection. Usually the metal plate is left in place for life but occasionally it is necessary to remove it if it becomes loose or the underlying bone becomes infected.
Within the knee joint there is a pad of cartilage called the meniscus. If this is damaged it can cause an ongoing lameness. Although the meniscus is examined during surgery and any damaged sections removed it is possible that undetected meniscus damage can cause the lameness to persist after surgery.
Cruciate disease injuries lead to arthritis of the knee which in many cases is already present before surgery. Although surgery can slow down or even stop the progression of arthritis it cannot reverse the changes that are already present and ongoing treatment of the arthritic pain may be necessary
What happens without surgery?
Without surgery the knee joint remains unstable leading to wear of the bone ends within the joint. This leads to arthritis associated with pain, lameness and reduced function of the leg. The knee joint becomes thickened with fibrous tissue which is natures attempt to stabilise the joint. In cats and small breed dogs (<15kg) this fibrous tissue may eventually stabilise the joint sufficiently for the leg to regain near normal function though ongoing pain relief may be necessary. Surgery is recommended as the best option for return to good function. With larger dogs (>15kg) the leg will never regain normal function without surgery and pain relief and restricted exercise will be needed for the rest of the dog’s life. The quality of life will be much reduced.