Cruciate Ligament Disease / Failure
What is a Cruciate Ligament and Why is it Important?
Inside the knee (stifle) of a dog there are two ligaments that cross over, hence they are called cruciate ligaments (see drawing). Their main role in life is to stop the tibia (shin bone) from moving forwards or backwards relative to the femur (thigh bone) when weight is put down through the joint. Without this support the joint would be unstable which will cause pain if weight is put on the leg and the excessive movement in the joint will encourage arthritis to develop.
What goes Wrong?
For reasons that are very poorly understood, one of the cruciate ligaments in dogs’ knees (labelled in the drawing above) is very prone to becoming progressively weaker and then failing, often following a minor injury such as getting up out of bed quickly or turning sharply to catch a ball / chase a cat. The problem is seen in virtually all breeds of dog of varying age (though it is uncommon in those less than 1 year of age). Although in some dogs the rupture of this ligament is a genuine injury (e.g. getting the leg caught up in a fence) in most it is a progressive disease of the ligament, although the eventual failure and onset of lameness might be quite sudden. Once the ligament has failed then any attempt to take weight on the leg will cause the tibia to be pushed forwards. This causes pain through stretching of the tissues around the joint and muscle wastage (particularly of the thigh muscles) that seems to be a reflex intended to protect the knee rather than just because of not using the leg. In addition, within the joint there are also two pads of cartilage called menisci. These help to stabilise the joint by acting as spacers between the femur and tibia. We also have these in our knees and they are the structures that footballers are always injuring! In an unstable knee it is possible for one of these cartilage pads to become damaged (occurs in about 30% of dogs with cruciate ligament failure) and this probably adds to the pain from the joint.
What signs will a Dog show if they have Cruciate Disease / Failure?
What signs a particular dog will show depends on the pattern of ligament deterioration in their particular knee. In some it is a very sudden onset of lameness following a minor injury (chasing a ball etc) whilst in others there is a longer history of stiffness after rest, lameness at exercise that deteriorates over weeks or months and then possibly shows a sudden deterioration (perhaps as a result of the ligament finally failing completely, or else because of additional cartilage damage as mentioned above). If they do have a sudden onset or sudden deterioration then some improvement is often seen over about one week followed by variable lameness but little improvement over the next few weeks (or months!) – see the next section. Another sign that owners sometimes notice is that they start to hear a “click” when their dog is walking. This is of some interest but does not mean anything specifically, nor does it have any affect on making a diagnosis, treatment recommendations or likely outcome.
A diagnosis will generally be made by a Veterinary Surgeon on the basis of detecting the instability in the joint as outlined above, where the tibia (shin bone) can be moved forwards relative to the femur (thigh bone) (a “cranial drawer sign”) – when this isn’t possible in the normal knee (except, to an extent, in puppies). This abnormal movement can be detected in some dogs when they are conscious but in many it is only possible to be sure of this when they are examined under anaesthetic – perhaps because moving the joint in this way is painful, causing them to tense up (or worse!). Although the ligament cannot be seen on an X-ray it is always advisable for these to be taken to make sure there is not another reason for the instability (including fractures). The X-rays of knees of dogs with cruciate ligament failure might show nothing more than there being too much fluid in the knee, but most will also show some signs of arthritis with new bone deposits starting to form around the joint.
What happens if we let this problem run its natural course?
Once cruciate ligament disease begins, and particularly if the ligament fails completely, then nature will try and stabilise the joint by making it arthritic. The scar (fibrous) tissue that forms around the joint will act like an internal bandage and help to stop the tibia from moving so much when weight is put on the leg. It is also quite likely that some dogs will be able to teach themselves how to use the muscles in the leg in a different way so as to help control the movement in the tibia – in a “functional” way. The latter is used extensively in human patients after cruciate ligament injury, with good success. However, in dogs the problem is a disease of the ligament rather than a true injury and so thinking of managing dogs in the same way as humans has, in the past, met with very different results.
In a study conducted many years ago to look at the outcome of dogs treated for this problem by letting it run its natural course (with some restriction of exercise and the administration of pain killers) the results showed the likelihood of regaining satisfactory function over a 5-6 month period was very closely related to the size of the patient – with smaller breeds having a much better chance than larger breeds. It is estimated that in dogs weighing about 30kg the likelihood of them regaining satisfactory function “on their own” so to speak, is about 30%.
There are two caveats to this result. One is that if such measures fail then any thoughts of surgical treatment at that stage ought to take into account that the expectations should be adjusted to take account of the degree of arthritis that will have developed (the surgery would still be of value but residual stiffness or mild lameness is more likely than if treatment had been carried out earlier). The second is that many dogs that develop cruciate failure in one knee will go on to develop it in the other knee. Studies following this seem to agree on the risk of the other leg becoming affected is about 60% within two years, across the board, and higher in Rottweilers! So how good a dog’s mobility will be after “natural” treatment of one leg might then become compromised if the other leg becomes affected later on.
What can we do to help – Surgery?
It has become well accepted, over many years, that surgical treatment of this problem tends to offer better outcomes then simply allowing nature to take its course. Success rates will vary as a result of many factors, including:
- Surgeon experience
- Technique used
- Patient (and Owner) co-operation with aftercare
Please note that the success rates outlined below are based on our continual monitoring of outcomes for patients treated at Weighbridge Referral Centre by Steve Butterworth, who has undertaken several hundred of each of the two main types of surgery used at this clinic to treat this problem over more than 15 years.
In the past, surgery has always been aimed at trying to use something to replace the cruciate ligament in a way that then prevents the tibia (shin bone) from moving forwards when the dog takes weight on the leg. These techniques, often referred to as “substitution techniques”, number over one hundred and all have met with similar results to those outlined below for this type of surgery. The most recent of these was developed by Professor Jimi Cook and is called the “Tightrope”. This, in his hands, produces similar results to those detailed below for the techniques involving “redesigning the knee” Although the reported results of the tightrope technique are better any advantage over the TPLO-type surgery, in terms of cost, is lost and the results of TPLO are comparable. At Weighbridge Referral Centre we have chosen one of the “substitution” techniques to use in appropriate patients – that of the Lateral Suture (see below).
Over the past decade a group of surgical techniques have evolved that aim to change the biomechanical forces within the stifle so that the tibia, put simply, does not want to move forwards rather than it being prevented from moving forwards. Essentially changing (“re-designing”) the knee so that it can manage without the cruciate ligament by creating what may be referred to as “functional stability”. The various techniques using this principle have some advantages and disadvantages compared with others in the group. At Weighbridge Referral Centre we use TWO of these (the tibial plateau levelling osteotomy – TPLO, and one form of tibial tuberosity advancement – TTA) in order to maintain what we consider to be a good success rate. Which of these two (TPLO or TTA) We recommend is dependant on assessment of the individual patient. If owners are interested to know more about this choice then Steve Butterworth is more than happy to discuss this further – though an interest in biomechanics would be helpful!
Lateral Suture Technique
An important part of the surgery is to look inside the joint to check for any damage to the cartilage pads and to trim away any injured part of these structures. Without doing this up to 30% of dogs might remain lame because of this problem.
The joint is then stabilised “mechanically” by placing a piece of very strong nylon around the back of a small bone just behind the knee joint and through one or two tunnels drilled in the front of the tibia just below the knee. Once tied this suture will prevent the tibia from moving forwards relative to the femur. However, if this was the end of the story then all these sutures would fail because of continual stretching – release – stretching – release – stretching etc, every time the dog put weight on the leg. But because the nylon is a foreign body, nature reacts to this and covers it in scar (fibrous) tissue and, ultimately, it is this that helps to stabilise the joint. In fact, if dogs with successful outcomes are examined under sedation 6 months after surgery, many of them have some instability in their knee. So why are they no longer lame? Perhaps because they have learnt to control the remaining (reduced) instability using their muscles in a different way – creating what is often called “functional stability” as opposed to “mechanical stability”.
The process of scar formation takes about 3 months and it is important that during this time the patient is restricted in his / her activities. They are allowed as much lead exercise (on a short leash) as they can tolerate – increasing the duration of walks as they recover. But they are not allowed freedom around the house or the garden, with no access to furniture or free access to stairs (can be walked up and down these if required, but not allowed to run up and down them at will). When not on the end of a lead they should be restricted to a pen or small room containing no furniture and with a non-slip floor. Once the three months has passed it is usually possible to steadily increase activity levels, with re-introduction of off lead exercise, over the next month or two.
So what results can be expected with this surgery? If there are no complications and the post-operative plan is kept to by the patient and their owners then the results are fairly consistent but influenced by the size of patient. In small breeds of dog, satisfactory results are seen in over 90% of cases, whilst in medium breeds this would be 80-90% and in large breeds about 70%. Of those considered satisfactory about half will be back to normal (as defined by their owners) and half will show mild signs of stiffness after rest or intermittent lameness at exercise. Of those that are unsatisfactory, a complication may be identified in a few that can be resolved with relative ease (i.e. without involving further major surgery such as TPLO).
Tibial Plateau Levelling Osteotomy (TPLO)
Again an important part of the surgery is to look inside the joint to check for any damage to the cartilage pads and to trim away any injured part of these structures. Without doing this up to 30% of dogs might remain lame because of this problem.
The joint is then stabilised “functionally” by changing the slope on the top of the tibia. It has been recognised that, in all dogs, the top of this bone is sloped (relative to the ground) almost all the time the dog has weight on the leg. This means the femur tries to slide off the back of the tibia, pushing that bone forwards. By cutting the bone in an arc and rotating that segment around it is possible to reduce the slope on the top of the bone. This will reduce the forces created in the joint such that the tibia is no longer being pushed forwards as leg is taken through the leg. The segment of bone then has to be stabilised using a specially designed bone plate whilst healing takes place. In most cases the bone plate stays in for good but occasionally it causes irritation and has to be removed.
The process of bone healing takes up to about 3 months and it is important that during that time the dog is restricted in his / her activities. They are allowed as much lead exercise (on a short leash) as they can tolerate – increasing the duration of walks as they recover. But they are not allowed freedom around the house or the garden, with no access to furniture or free access to stairs (can be walked up and down these if required, but not allowed to run up and down them at will). When not on the end of a lead they should be restricted to a pen or small room containing no furniture and with a non-slip floor. Once the three months has passed, and preferably an X-ray has shown bone healing is complete, it is usually possible to steadily increase activity levels, with re-introduction of off lead exercise, over the next month or two.
So what results can be expected with this surgery? If there are no complications and the post-operative plan is kept to by the patient and their owners then the results are fairly consistent and NOT influenced by the size of patient. Satisfactory results are seen in over 90% of cases. Of those considered satisfactory about two-thirds will be back to normal (as defined by their owners) and the other third will show mild signs of stiffness after rest or intermittent lameness at exercise. Of those that are unsatisfactory, a complication may be identified in most that can be resolved with additional treatment.
How do we choose which technique to use?
Both these techniques are discussed at the time of consultation. In general, the recommendation from Steve Butterworth will be that of a lateral suture in small breed dogs and TPLO in medium and large breeds. However, some small breed dogs have a very steep slope on their tibia and so TPLO might be considered, despite their size. In addition, owners have to take the financial aspects into consideration as TPLO surgery is far more involved in terms of technique and instrumentation and requires the use of a bone plate and screws, all of which makes it a more expensive treatment compared with a lateral suture. The final decision is taken by an owner once they are in a position to make an informed choice.
Tibial Tuberosity Advancement (TTA)
Again an important part of the surgery is to look inside the joint to check for any damage to the cartilage pads and to trim away any injured part of these structures. Without doing this up to 30% of dogs might remain lame because of this problem.
In a normal stifle (knee) joint of a dog (left hand drawing), when weight is put on the hindlimb (blue arrow 1) a force is created that tries to move the tibia forwards (blue arrow 2). Normally this is resisted by, not only the cruciate ligament, but also forces generated by the muscles. In particular the pull of the thigh (quadriceps) muscle (red arrow 1) creates a force that pushes the tibia backwards (red arrow 2). If the cruciate ligament has failed then, if weight is put on the limb, the tibia will move forwards because the tibial thrust (blue arrow 2) exceeds all the forces from the muscles (including red arrow 2). However, the joint can be stabilised “functionally” by advancing the tibial tuberosity. This has the effect of changing the action of the powerful quadriceps (thigh) muscle so that the force depicted by red arrow 2 (in the right hand drawing) is increased and matches or exceeds the tibial thrust (blue arrow 2). This will then hold the tibia back in its correct position In order to advance the point at which the tendon attaches to the bone, a cut is made down the bone and then the segment at the front is moved forwards, openening up a gap that is wedge-shaped. A titanium cage (size required calculated from X-rays) is then placed in the gap and secured with titanium screws (right hand drawing). The gap is then filled with a synthetic bone graft substitute to speed up the healing process.
The process of bone healing takes up to about 2-3 months and it is important that during that time the dog is restricted in his / her activities. They are allowed as much lead exercise (on a short leash) as they can tolerate – increasing the duration of walks as they recover. But they are not allowed freedom around the house or the garden, with no access to furniture or free access to stairs (can be walked up and down these if required, but not allowed to run up and down them at will). When not on the end of a lead they should be restricted to a pen or small room containing no furniture and with a non-slip floor. Once the three months has passed, and preferably an X-ray has shown bone healing is complete, it is usually possible to steadily increase activity levels, with re-introduction of off lead exercise, over the next month or two.
So what results can be expected with this surgery? If there are no complications and the post-operative plan is kept to by the patient and their owners then the results are fairly consistent and NOT influenced by the size of patient. Satisfactory results are seen in over 90% of cases. Of those considered satisfactory about two-thirds will be back to normal (as defined by their owners) and the other third will show mild signs of stiffness after rest or intermittent lameness at exercise. Of those that are unsatis factory, a complication may be identified in most that can be resolved with additional treatment.
How do we choose which technique to use?
Thes three techniques are discussed at the time of consultation. In general, the recommendation from Steve Butterworth will be that of a lateral suture in small breed dogs and TPLO/TTA in medium and large breeds. However, some small breed dogs have a very steep slope on their tibia and so TPLO or TTA might be considered, despite their size. Which of the TPLO or TTA is most appropriate for a particular individual is decided upon by assessment of radiographs of that individual. In addition, owners have to take the financial aspects into consideration as TPLO/TTA surgery is far more involved in terms of technique and instrumentation and requires the use of orthopaedic implants, all of which makes them more expensive treatments compared with a lateral suture. The final decision is taken by an owner once they are in a position to make an informed choice.