Feline cruciate rupture

Cranial cruciate ligament (CCL) rupture in the dog ranks 2nd to none as subject matter in veterinary orthopedic literature. It is most often a degenerative condition that has a genetic basis, and an offending allele has recently been isolated (1,2). By comparison, relatively little has been written about cruciate ligament rupture in the cat. Prior to the last 20 y, rupture of the feline cruciate ligament was generally described as or assumed to be of a traumatic etiology and its surgical repair was documented in individual cases (3–6).

Traumatic cruciate ruptures commonly occur as a result of falls. Cats with so-called “apartment syndrome,” that is fall from significant heights, may suffer stifle injuries, among other traumas. While rupture of the CCL is common in those circumstances, it is almost always part of “polytrauma” to the stifle. Caudal cruciate and medial collateral ligament injuries are most commonly associated with this type of trauma, along with meniscal tears in at least 50% of these cases (7,8).

Cats that develop CCL ruptures with little or no apparent trauma generally rupture the CCL only, but they may also have medial meniscal tears. Such cats are commonly overweight and the histological picture of their torn CCLs mirrors that of the degenerative changes that have been described in dogs: irregular arrangement of collagen fibers, fibrocyte proliferation, and occasional dystrophic mineralization.

In 9 cases of degenerative feline cruciate ruptures in 8 cats in our practice, the cats averaged 8.5 y of age and had a mean weight of 6.5 kg, which was a significantly higher average weight (P = 0.03) than that of a sampling of our practices general feline population. Significant differences in age or sex distribution could not be demonstrated (8). This population of cats with CCL rupture mirrored the profile of dogs with CCL rupture in our practice before 1991. In a survey of 165 dogs with CCL rupture, conducted from 1983 to 1990, 78% were small breeds (under 15 kg), with a mean age of 8.7 y. Many of these dogs were overweight (9).

Diagnosis of feline CCL rupture is usually easily confirmed on physical examination. Drawer motion is pronounced in most affected cats. Radiographic signs are similar to those seen in the dog and may include joint effusion, degenerative joint disease, and distal displacement of one or both popliteal sesamoid bones (10). Dystrophic mineralization, which can be seen radiographically in any stifle joint with CCL lesions, seems to be more common in the cat. The mineralization is most often located at the insertion point of the CCL on the cranial aspect of the tibia, but mineralization of a meniscus may also develop.

While feline CCL rupture is not rare, it is not nearly as common as in the dog. This may be because the CCL in the dog is smaller than the caudal cruciate ligament, whereas the reverse is true in the cat (11). It may be that the genetic inheritance of CCL rupture documented in the dog is absent or less likely in the more heterozygous feline population. The smaller size of cats is also a potential factor, since degenerative changes in stifle joints are known to be more severe and to occur earlier with increasing weight (12). Finally, the prevalence of CCL rupture in the cat is likely to be under-reported, since more cats than dogs appear to recover from this lameness without treatment.

A possible link between feline CCL rupture and hypertrophic cardiomyopathy, which may also involve hyperthyroidism, has been proposed. The death of 2 cats shortly after CCL rupture repair and a subsequent necropsy diagnosis of hypertrophic cardiomyopathy has been reported (13). Two of the 8 cats in our survey were diagnosed with hyperthyroidism within 2 y of their CCL surgery. The connection between hyperthyroidism and hypertrophic cardiomyopathy has been well documented.

Treatment of CCL rupture in cats is not without controversy. Multiligamentous traumatic injuries can be stabilized by ligament reconstruction techniques or the placement of a transarticular pin (7,14). The “dogma” concerning degenerative CCL rupture in cats has favored conservative therapy, including confinement and nonsteroidal anti-inflammatory medication. This recommendation is based primarily on 1 publication detailing the results of 16 cats (15). Published results of extracapsular surgical repair in cats, including those of our own practice survey, indicate that results are at least as good as those achieved with conservative treatment, and that surgery provides quicker and more reliable return to function (8).