Cranial cruciate ligament injury in dogs - are we really making any progress?

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“Rupture of the cranial cruciate ligament is seen for the most part in active jumpers, and especially in those individuals (dogs) having the defect in conformation where the stifle and tarsus are carried in overextension. The absence of the normal flexion angle of these joints in the standing position appears to be a predisposing cause. Fixation (immobilization) for from three to six weeks will in most cases result in a recovery that at least approximates perfection as far as function is concerned.”

 –Erwin Schroeder 1939

After 25 years in veterinary surgery, I have become a bit of a sceptic. Our profession is inundated with poorly documented “dogma”, and the flawed logic that if enough intelligent people believe something to be true, then it must indeed be true. Evidence is frequently derived from uncontrolled case series, clinical case reports, the opinion of “experts” and “personal experience”. Well designed, placebo controlled, randomised and blinded prospective clinical studies are exceptionally rare. Perhaps nowhere is this problem more glaringly obvious than in our present approach to the clinical management of dogs with cranial cruciate ligament (CCL) injury.

CCL injury is one of the most common injuries encountered by veterinarians, and is by far the most common cause of lameness of the stifle joint (Ness and others 1996). Early surgical stabilisation is generally recommended, particularly in dogs weighing more than 15kg, because poor results are reported for most dogs that undergo non-operative management (Vasseur 1984). The Wall Street Journal recently reported that the incidence of cruciate ligament surgery in dogs actually exceeds that in humans in the USA, and the estimated repair costs of these surgeries was about 1.23 billion dollars in 2003 (Helliker 2006, Wilke and others 2005). Despite these staggering figures, it was recently demonstrated that not a single surgical technique consistently returns dogs to normal function (Aragon and Budsberg 2005).

Management of CCL injury by stabilisation of the stifle with a lateral fabellotibial suture (LFS) has been performed for over 30 years, and is generally considered to be quick, affordable, and safe. Problems with implant reaction and infection were initially reported to be common, but dogs in these early studies had been implanted with multifilament suture of questionable sterility from cassettes (Dulisch 1981). Implant loosening continues to be an issue, but problems have decreased with recent identification and utilisation of more isometric attachment sites (Roe and others 2008). It is often suggested that the great majority of dogs weighing less than 20 kg will return to near normal function after LFS, but larger and more athletic dogs will only have a fair outcome. Despite common usage of this surgical procedure for more than a third of a century, neither of these assumptions has ever been verified in a controlled clinical study. In fact, the only quantitative data available suggests that in at least one large breed dog (the Labrador retriever), animals will obtain a very respectable 95 percent of normal weight bearing by six months after surgery (Conzemius and others 2005).

In 1993, Dr Barclay Slocum revolutionised our thought process to CCL injury when he introduced the concept of dynamic (rather than static) function of the stifle, and first described treatment of CCL injury by tibial plateau levelling osteotomy (TPLO) (Slocum and Devine 1993). Access to TPLO was initially limited as both the procedure and implants were patented, but when patent rights expired TPLO became much more widely available. Recently, TPLO seems to have taken on a life of its own, with instrument companies flocking to the fray to produce new implants of every shape, size, and color. Popularity of this technique has now increased to the point that in some hospitals it is the most commonly performed treatment for CCL injury in all sized dogs and even cats.

Since its conception, TPLO has been the subject of tremendous discussion and debate. Early studies confirmed that the procedure is mechanically sound, and provides improvement in clinical function (Warzee and others 2001, Slocum and Devine 1993). Arthritis still develops, but at a slower rate than with LFS (Lazar and others 2005). The “professional opinion” of the great majority of veterinary surgeons (including my own) is that young, large, athletic dogs will often perform better after surgery with a TPLO than LFS. Unfortunately, although there is extensive literature describing the mechanics of TPLO and fine nuances of surgical technique, there is not a single piece of scientific evidence to support the belief that it is clinically superior. In the only well controlled prospective study comparing techniques, Dr Conzemius reported that weight bearing on a force plate was not statistically different between TPLO and LFS two months and six months after surgery, and both groups were significantly different from normal at all time intervals evaluated (Conzemius and others 2005). I have always argued that a major limitation of this study is that the dogs were walked over the force plate after rest, and perhaps a significant difference would have been detected after a period of exercise. It is also possible that differences in the two groups would have been noticed with longer follow-up. Despite these study limitations, it is clear that contrary to the statements of many veterinary surgeons, TPLO is certainly not markedly superior in clinical outcome to the less expensive, less risky, and more easily performed LFS.

Tibial tuberosity advancement (TTA) and triple tibial osteotomy (TTO) are the most recent advances in our surgical armamentarium for treatment of CCL injury in dogs. Each of these techniques attempts to stabilise abnormal stifle motion after CCL damage by advancing the patellar tendon into a position perpendicular to the tibial plateau. Like TPLO, the opinion of most veterinary surgeons is that these procedures are better than LFS for large athletic dogs. Mechanical evaluations have been performed, and fine nuances of surgical technique described (Apelt and others 2007, Lafaver and others 2007). TTA has been previously reported to give good results in a large majority of patients with minimal complications (Lafaver and others 2007), and similar encouraging outcome is reported after TTO in this issue of JSAP (Renwick and others 2009). What is missing, however, is a single piece of scientific evidence that confirms that either TTA or TTO is actually superior to other more simple surgical procedures.

It may seem that I am not a “believer” in any of the recently developed surgical techniques for management of CCL injury, yet I am. Personally, I perform surgery on several hundred dogs each year with a variety of surgical techniques including LFS, TPLO, and TTA. Although I have not performed TTO, the mechanics are identical to TTA, and clinical outcome should be the same. My professional opinion is that large athletic dogs generally perform better with TPLO or TTA, and when an owner asks the inevitable “what would you do if it were your dog” question I usually choose one of these techniques. That being said, I also firmly believe that LFS gives a very good outcome in most dogs, in fact better than TPLO or TTA in some cases. We recently reported that the complication rate with LFS is less than that reported for either TPLO or TTA, and some owners are firmly opposed to taking any increased risk (Casale and McCarthy 2009). In the current global economic climate financial considerations are more important than ever. In my practice the cost of performing TPLO or TTA is about double that of LFS and for many owners it comes down to the financial reality of either performing LFS or leaving the problem totally unaddressed.

So where should we go from here? Initially I think we need to simply slow down. Manufacturing of the implants and clinical use of the procedures are greatly preceding any real science on the clinical advantages or disadvantages of the procedures themselves. Surgical techniques already in common clinical use need to be evaluated more carefully and any new procedures developed should be examined more critically before widespread clinical application. We need to prove that more expensive and invasive surgical methods are warranted before asking clients to pay for them.

More scientific inquiry like the articles in this issue of JSAP is vital.

Dogma, common belief and professional opinion need to be questioned, evaluated, and authenticated. For example, veterinary students are generally taught that cranial drawer motion is the “gold standard” for diagnosis of CCL injury, yet in this issue of JSAPCarobbi and Ness (2009), demonstrate that cranial drawer motion is only present in about 60 per cent of dogs with confirmed CCL damage. A critical unanswered question continues to be the issue of why we are seeing such an explosion of CCL cases worldwide and what can we do to prevent it? Steepness of the tibial plateau slope has been investigated, but data is generally inconclusive (Morris and Lipowitz 2001, Wilke and others 2002). Genetic influence has been demonstrated in the Newfoundland breed, but what role the genes play in causing the injury is unknown (Wilke and others 2006). Dietary and hormonal influences are being investigated, and need to be much more extensively evaluated.

Seventy years ago Dr Erwin Schroeder suggested that we could obtain “near perfection as far as function is concerned” by immobilising the knee of dogs with CCL injury in a bandage. Twenty-five years ago we performed surgery on a small number of dogs each year using a simple technique that could be accomplished by a large number of private practice surgeons. Expected clinical outcome in these cases was about 90-95 per cent of normal. In 2009, we have a plethora of complex surgical techniques that involve fractures, advanced surgical instrumentation and expensive implants. Expected clinical outcome in the majority of dogs is around 95 per cent of normal. Clearly there is still work to be done!

Rob McCarthy graduated from Tufts University School of Veterinary Medicine in 1983 and has been a Diplomate of the American College of Veterinary Surgeons since 1992. He is currently Clinical Associate Professor at Tufts as well as owning a private surgery referral practice. His special interests include cranial cruciate ligament injury, canine elbow dysplasia, minimally invasive surgery (arthroscopy, thoracoscopy, laparoscopy), antibiotic usage, and diseases of growing dogs.

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