The normal function of the knee in dogs is dependant on the stability provided by two ligaments that form a cross within the knee called cruciate ligaments (crux = cross in Latin). The anterior cruciate ligament is the one most commonly injured, as it is the main structure preventing the knee from overextending (over straightening). In a dog it is needed with every step to prevent the bottom of the femur bone from sliding down the slope of the upper plateau of the tibia bone (an anatomical difference between people and dogs).
Tearing of the anterior cruciate ligament is the most common reason for lameness/limping in the hind limb of medium to large breed dogs. The partially or fully torn ligament becomes painful and prevents normal weight bearing use of the affected hind leg. Dogs will quickly loose muscle mass on the affected leg as the lameness worsens, and will often choose to sit with the affected leg extended to prevent the pain associated with bending the knee. Eventually a partially torn ligament under the stress of normal activity will completely tear, resulting in worsening pain and arthritis. Osteoarthritis develops rapidly once the ligament completely ruptures. More than 30% of dogs also go on to rupture the anterior cruciate ligament in the other hind leg, usually within 18-24 months. A possible explanation for this phenomenon is the degenerative process usually progresses in both joints, with the “healthy” joint experiencing extra load once the first knee is injured.
The knee also has 2 menisci/floating cartilages in the joint, a bit like a rubber tap washer cut in half, to help cushion the weight-bearing forces in the joint. Unfortunately, once the cruciate ligament is torn, the menisci are vulnerable to shear forces with every step and frequently end up torn and also contribute to pain, inflammation and the formation of bony arthritis in the joint.
Diagnosis
Veterinarians are trained to diagnose cruciate ligament injuries with a combination of examinations, sometimes also accompanied by x-rays (to gain further evidence of cruciate ligament injury and to rule out other causes of hindlimb lameness). Some animals are quite nervous when in a vet clinic and also in quite a bit of pain with the injury. Therefore, in some patients, examination under sedation or general anaesthesia is required to make a diagnosis.
Common findings on knee examination include:
- Extra joint fluid/swelling (joint effusion).
- Bony swelling on the inside of the lower part of the joint (tibial buttressing).
- Muscle wasting/atrophy.
- Knee pain with forced straightening/extension.
- Craniocaudal instability/ scissoring movement front to back (cranial draw and tibial thrust tests).
Sometimes there is no instability and it can be challenging for us as vets to know if the ligament is normal or not.
Treatment options
All patients with cruciate ligament injuries or other synovial joint problems significantly benefit from long-term dietary supplement with high quality omega 3 & 6 fatty acids/oils and also a source of glucosamine or other polysulfated glycosaminoglycans (PSGAGs). This can be easily achieved by feeding a commercial prescription diet (dry food) made by Hills pet foods (Hills J/D – joint diet) sold only from veterinary clinics or by adding omega oils and glucosamine or shark cartilage powder to the food. As an additional therapy many patients before or after surgery are given a course of 4 injections of a drug called Synovan that is a concentrated form of PSGAGs that can be used by the body to help heal joint surface cartilage and keep joint fluid at a high quality/viscosity to lubricate the joints.
Conservative treatment
In some cases, conservative, non-surgical treatment is trialled. This involves strict confinement/restriction of exercise to a small (2x4m) area (laundry or small dog run) and only exercised in controlled fashion on a lead for short periods for toileting needs, for 4-8 weeks. These patients are usually also on a non-steroidal anti-inflammatory medication to control pain and reduce swelling and inflammation (Meloxicam, Metacam, Previcox or Carprieve ). This initial option is often undertaken in small breed dogs or where the dog’s advanced age leads to unacceptably high risks from a general anaesthetic, or where available funds limit the owner to non-surgical options.
Surgical options
Open joint surgery is the standard technique to observe the cruciate ligaments & menisci directly, and allow removal of any damaged structures. This helps to slow the arthritic process and is performed in all dogs undergoing cruciate surgery. Another purpose of surgery is to try and slow down the degenerative/ arthritic process by stabilising the knee joint and preventing the shear forces when the dog is weight bearing on the affected leg. There are two basic surgical options to achieve this.
In smaller dogs it is common to insert prosthesis to take on some of the role of the missing cruciate ligament. This technique is called a “DeAngelis suture”. It involves precisely placing a tough nylon suture material and a stainless steel crimp (instead of a knot) just outside the knee joint. It is anchored to the back of the femur and through 2 bone tunnels just under the top surface of the tibial crest, and runs in the same direction as the original cruciate ligament. This is the quickest and least costly surgical option, but has some limitations. Despite using the most modern materials this suture frequently over time either breaks or stretches, particularly in medium to large breed dogs, though the joint capsule has usually thickened up and taken on some stabilizing role as well.
The most appropriate surgical technique for large breed dogs involves placing small cut/s to the bone of the top of the tibia to alter the angle of shear forces in the knee joint so an anterior cruciate ligament is not required and the intact caudal cruciate ligament takes on some of its role. This involves cutting the bone, adjusting the angles of tibial plateau relative to the femur and patella (kneecap) ligament, and then placing a stainless steel plate & screws to maintain the new position while the bone mends. The angle of change required is calculated after x-rays are taken prior to surgery and precision cutting blades and guides are used to achieve this. This surgery requires more equipment, implants and time and is therefore more expensive, but results in superior long term results (less arthritis and fewer late meniscal injuries requiring a second surgery).
Post-op pain control
We use a combination of local anaesthetic, opiod and non-steroidal anti-inflammatory injections and tablets or syrups before, during and after surgery in the clinic to ensure a pleasant recovery from cruciate surgery, and most patients are sent home with an anti-inflammatory medication for 10-20 days post op for use at home. Particularly sensitive patients may also be given an opiod pain control medication (Tramal) if needed. Intravenous drips and intravenous antibiotics are given during surgery, and in the hours after surgery, to help ensure very few complications are experienced by our patients. In some cases, antibiotics may be dispensed for home medication for the days following surgery.
Potential complications:-
Potential complications from anaesthesia or surgery include but are not limited to:-
Anaesthesia - the risk is extremely low but will never be zero. The individual dedicated to the patients anaesthesia monitors body temperature, respiration and heart rates, pulse oximetry (oxygen saturation of the blood) and blood pressure.
Infection - like anaesthesia, the risk will never be zero. We take every precaution to prevent infection. Assurance that the skin is clean by bathing your pet before surgery is just one precaution. Surgery will NOT be performed if the skin is unhealthy where we are going to operate, or if an infection has been detected in other parts of the body i.e. skin, teeth, ears or urinary tract. Infection can arrive at the implant through the blood, some time later in life. It is therefore important if your pet gets an infection in the future that it is treated promptly by a veterinarian and probably with antibiotics.
Loosening of the components of any of the surgery techniques, can happen with time. The probability of this happening is proportional to the level of activity of the patient, and their size and bodyweight. Extremely active patients i.e. working dogs, small terriers and Staffordshire terrier type patients that work and play strenuously are more likely to loosen (or break) implants.
Luxation of the patella (kneecap) - can occur as a result of a fall or overactivity especially during the first 4 weeks post-op. Being careful to avoid falls and the patient going ‘spread-eagled’ postoperatively is extremely important.
Pulmonary embolism also referred to as lung clots. It is extremely rare that a canine patient would not cope with the small size and number of emboli that may travel to lungs during surgery. However when this complication arises and then leads to blockage of blood vessels in the lungs, it can be fatal.
Please be assured we take every precaution to minimise all risks as we strive to improve the quality of your pet’s life. Nursing care at home is very important, and we count on you as the owner to be part of the team and follow our aftercare instructions carefully. Avoiding complications is as important to us as it is to you. With this in mind we strive to avoid additional surgery as well as to prevent the extra expense you would incur.
Recovery from surgery
Canine orthopaedic patients need to be carefully rehabilitated just like human patients after joint surgeries. This involves strict confinement (e.g. a small dog run , the laundry, small section of the garage or a playpen for the small patients) but with some early “physiotherapy” of the joint, and a controlled exercise program (with incremental increases in activity over a full 12 week period after surgery). Post-op your dog will have a shaved leg and a row of sutures over the area either inside or outside the knee joint. In the first 10 days they benefit from 5 minutes twice daily of passive bending and straightening of the knee, just the range of movement they will tolerate, to encourage early return to function. This is done with the patient lying on their side with the operated on knee uppermost, one person comforting and restraining the patient and the other manipulating the knee.