Prospective Clients
Knee Joint Overview
The knee joint, unlike a ball and socket joint such as a hip that is very sturdy because the articulating bones fit closely together, relies completely on ligaments inside and around the knee joint to maintain strength and stability. When any of these break down, mobility problems occur.
There are a few very important structures inside the knee (or stifle) joint of a dog or cat necessary for normal function, namely the cranial (anterior) cruciate ligament (ACL); the caudal cruciate ligament, and the two menisci (cartilages). The two structures that most commonly present problems are the ACL and the medial meniscus, and Dr. Wurdell’s surgical services are concentrated on them.
The Anterior Cruciate Ligament (ACL)
The ACL has actually two parts like two ropes and is very strong. Both parts originate in the upper bone (femur) and attach to the lower bone (tibia) and are essential to keeping those two bones in alignment with each other, preventing the tibia from sliding out in front of the femur and also preventing the tibia from rotating under the femur.
ACL problems are by far the most common cause of persistent hindlimb lameness in adult dogs. There are theories as to why but trauma is a rare cause. In the vast majority cases, the ACL seems to degenerate on its own. Normal aging produces gradual weakening of the ACL but in some individuals this weakening progresses to more advanced degeneration and sometimes to complete disappearance. In this scenario, it is a question of when, not if, ACL problems arise in some individuals and why many dogs will eventually have the same problem with their other knee. ACL problems in cats are thought to be more likely to be due to trauma.
Unlike human beings, dogs and cats stand and walk and run with a bent knee. The ACL is thus loaded with weight all the time, making it integral in mobility. When the ACL is weakened, weight bearing becomes painful and persistent or recurrent lameness ensues even after a few weeks or more of rest. An abnormal ACL never heals, and even a mild to moderate degeneration will eventually progress to a complete loss of integrity. Like a rope, once it starts to fray, it won’t get better. The process never works in reverse.
Menisci or Cartilages
The menisci are 2 slightly concave C-shaped smooth cartilage pads facing each other on the top of the tibia (medial and lateral) that make a smooth seat for the femur to sit on and bear the weight of the body above. When the ACL is fully degenerate in a dog, and abnormal movement- the tibia sliding forwards - is occurring, these menisci can be crushed or torn by the weight of the femur grinding over them. The medial, or inside, meniscus is most prone to injury after ACL degeneration and in many cases, there develops subsequent permanent medial meniscal damage that compounds the initial ACL problem. Un-treated meniscal damage prevents normal return to knee function even after successful ACL surgery.
Cats tend not to damage menisci very commonly.
Surgery
Information
What are the symptoms of ACL Problems?
There are two common scenarios that prompt a visit to the veterinarian.
The first is a partial tear, or more likely, early degeneration. This is often a dog that presents with rear lameness after running and vigorous exercise. The dog may be tender putting its foot down when standing as though it has a sore foot, and after a few days of rest it might seem back to normal. When he goes out and runs again, he comes back lame again and again. This knee may not be unstable since partial ACL function remains; however, once the ACL breakdown process begins unfortunately these individuals will eventually progress to the second type. These individuals should go to surgery before the ACL deteriorates further to minimize secondary permanent osteoarthritis and avoid injury to the important menisci.
The second type of ACL problem presents with more acute severe hindlimb lameness, perhaps suddenly non-weight bearing when standing and very lame when walking. This is more likely a fully torn or degenerate ACL with overt knee instability. These dogs often were part of the first group initially and progressed. There are now also rotating and sliding forces on the mensci threatening to compound the problem through secondary meniscal crush or tear.
How is ACL injury diagnosed?
Diagnosis starts with your veterinarian assessing the history and completing a thorough physical examination. There are specific tests the veterinarian will complete to assess for possible ACL disease. Pain localized to the knee, or joint swelling, with or without instability also raises the suspicion. Sedation will likely be needed to relax the patient as the doctor is looking for subtle changes. Radiographs might be ordered to confirm the diagnosis.
How is Meniscal injury diagnosed?
If your dog has a stable knee with a partially torn or degenerate ACL, i.e. the earlier stages of an ACL problem, meniscal injury is unlikely. However in the case of an unstable knee with a fully torn ACL, secondary meniscal injury is common- perhaps 50% or more of the dogs that completely lack an ACL will develop secondary medial meniscal injury by the time of surgery. Some of these cases will have an audible click or pop when walking, but most cases of meniscal injury are quiet and can only be diagnosed by direct examination in surgery. Radiographs are not helpful. For that reason, all cases of fully torn or degenerate ACL’s need to have their stifle joint opened and menisci directly examined while in for ACL surgery. These dogs need two surgeries- one for the torn ACL and a second surgery to open the knee joint to directly examine the menisci and remove torn or damaged parts if needed. Without addressing a secondarily damaged meniscus, ACL surgery on its own will not produce good results.
How is ACL surgery done?
There are 2 most common categories of ACL surgery available.
One category is what is known as a geometry-modifying technique such as the tibial tuberosity advancement (TTA) or the tibial plateau leveling osteotomy (TPLO). These are procedures that stabilize the knee by transferring the work of the old ACL onto the patellar ligament (the big ligament that attaches the front thigh muscles and kneecap to the tibia below). An ACL then is no longer needed.
The premise of TTA is cutting the front part of the tibia just below the knee (the tibial tuberosity) from the main body of the tibia and moving it forward, then holding it in the new position with a titanium plate and spacer; the gap made by moving it forward is packed with a bone graft, and after 6-8 weeks the new bone should be solidly healed permanently.
TTA is suitable for all dogs but is considered best for 40lb dogs and heavier including giant breeds; it is also best for young active energetic dogs.
The second category of repair or stabilization is use of a single or double sturdy monofilament suture outside of the joint to take up the work of the old ACL. This is termed “extracapsular repair”, or “ex-cap". The sturdy suture will eventually break down after several months or longer, but in the interim it provides temporary stability of the joint until the dog or cat can form permanent scar tissue to tighten around the joint to keep it stable after the suture breaks down. Extracapsular repair is generally reserved for dogs under 40 lbs. and cats.
My surgery service uses the TTA method or the extra-capsular repair.