Cranial Cruciate Ligament Injury

In a study recently published in Acta Veterinaria Scandinavica,¹ cats with a previous diagnosis of unilateral cranial cruciate ligament (CCL) injury displayed gait patterns and owner-assessed behavioral changes that differed from those of sound cats.

Older cats frequently suffer from appendicular joint osteoarthritis (OA),² which is quite painful and limits a cat’s physical abilities. Like other orthopedic conditions, feline OA can cause a body weight (BW) redistribution away from the affected limb.³ Diagnosing OA in cats remains a challenge, in part because cats are so adept at disguising their lameness.⁴ In addition, radiographic results are not always consistent with orthopedic examination findings in cats suspected of having OA, despite radiography being the primary diagnostic tool for identifying this condition.⁵

Kinetic data, such as measurement of peak vertical force (PVF), has proven useful in assessing feline appendicular OA. PVF is measured as a percentage of body weight (% BW) and is evaluated using a pressure-sensitive mat, which can detect gait pattern abnormalities potentially associated with OA. In a prior study comparing cats with coxofemoral joint OA and sound cats, hindlimb PVF was lower in cats with OA than in sound cats.⁶

CCL injury alters the normal mechanics in the feline stifle joint, contributing to OA. In previous studies, CCL transection has been used to demonstrate the degenerative changes associated with OA. In one study, CCL transection led to significantly decreased muscle mass in the experimental hindlimb compared with the contralateral hindlimb.⁷ In addition, the synovium within the experimental stifle joint was hypertrophic and hemorrhagic; medial joint capsule thickening and osteophyte formation were also present.

The exact etiology of feline OA is not yet known. There is continued debate within the veterinary community about whether obesity contributes to OA in cats, as it does in humans.⁸ Dr. Sarah Stadig, the lead author for this current study on feline CCL injury, offered her comments on obesity’s role in feline OA development. Based on her clinical experience, Dr. Stadig says there is “likely to be an association between OA and [excess weight] or obesity in cats.” However, she notes that “we cannot say whether [excess weight] or obesity contributes to OA or if the cats with OA are less physically active and therefore become overweight or obese.”

For this current study, authors used a patient database from a local animal hospital to select cats aged 1 to 12 years with a previous diagnosis of unilateral CCL injury (n = 10). Sound cats (n = 15), selected from a prior data set,⁹ were weight and body condition score (BCS)-matched with the cats with previous CCL injury to rule out the influence of weight on kinetic data.

Authors used a pressure-sensitive walkway to collect kinetic data on PVF and vertical impulse (VI; % BW*sec). After acclimatizing to the testing room, each cat walked along the walkway until it completed five valid trials—a straight walking path at an even pace with a forwardfacing head position. Following kinetic data collection, each cat underwent a clinical and orthopedic examination. The clinical examination included BCS assessment using the 5- and 9-point scoring systems; joint changes were categorized as mild, moderate, or severe during the orthopedic examination.

Cats with previous CCL injury and normal blood work were then sedated for radiographic examination of the joints determined to be affected on orthopedic examination; sound cats did not undergo blood sampling or radiography.

During kinetic data collection, cat owners completed a questionnaire asking them to classify behaviors within four behavioral domains (mobility, activity, grooming, temperament) as normal or abnormal in their cats. Owners rated abnormal behaviors from 1 (mild) to 10 (severe).

A significant difference in average age was observed between cats with previous CCL injury (9.5 years ± 1.8) and sound cats (5.9 years ± 3.3). Because the sound cats were BCS-matched with the cats with previous CCL injury, no correlations between body weight, BCS, and gait parameters were identified.

Compared with sound cats, cats with previous CCL injury had a significantly lower hindlimb PVF and significantly higher front limb/hindlimb symmetry index for PVF; VI was also lower in cats with previous CCL injury, but this was not statistically significant. In cats with previous CCL injury, PVF and VI were significantly lower in the affected hindlimb versus the unaffected hindlimb.

To analyze vertical force distribution within the paws, authors divided the hind and front limb paw prints into equally-sized quadrants: craniomedial, craniolateral, caudomedial, and caudolateral. Pressure distribution within the hindlimb paw quadrants varied between cats with previous CCL injury and sound cats; in each quadrant, PVF was lower and duration of stance phase was longer with cats with previous CCL injury. Significant differences in pressure distribution within the front limb paw quadrants were not observed between cats with previous CCL injury and sound cats.

Total scores on the questionnaires were significantly higher for cats with previous CCL injury than sound cats, indicating physical dysfunction and a negative change in daily activities due to CCL injury.

Authors suggested that biomechanical instability of the stifle joint and physical discomfort could explain the differences in kinetic data, particularly PVF, between the cats with previous CCL injury and sound cats. For cats with previous CCL injury, the pressure asymmetry observed between the affected and unaffected hindlimbs could be explained by stifle joint instability, as well as muscle atrophy and a different gait pattern to minimize pain in the affected limb. However, the pressure asymmetry does not have to be pain related; clinical examination findings would aid in determining why the pressure asymmetry is present.

Because cats in this current study were pet cats with naturally occurring OA, it is possible that OA was present in more than just the affected stifle joint; authors noted that this could be a limitation with studying naturally occurring OA, rather than experimentally inducing OA, such as with CCL transection. In addition, pressure-sensitive mats have a limited ability to detect bilateral changes in gait pattern; this limitation could be avoided by analyzing the pressure distribution within the paws.

Given the challenges in diagnosing feline OA, authors emphasized the need for improved assessment tools to evaluate chronic pain associated with OA. Dr. Stadig suggested the use of clinical metrology instruments (CMIs), also known as questionnaires. She said that “CMIs can be used both for screening for OA and other problems in the musculoskeletal apparatus, as well as evaluating ongoing treatment,” noting that “several CMIs for cats with musculoskeletal disease are undergoing validation at the moment.” Dr. Stadig believes it would be useful for a “cat owner to fill in the CMI before the vet performs the clinical examination.”

Because radiographic findings are not always consistent with orthopedic exam findings, Dr. Stadig commented that veterinarians could use a pressure-sensitive mat in clinical practice to evaluate a cat for OA. To use the mat most effectively, Dr. Stadig advises veterinarians to take a simultaneous video recording and be aware of “common sources of errors, such as a cat looking to the side” when walking on the mat.

Dr. JoAnna Pendergrass received her doctorate in veterinary medicine from the Virginia-Maryland College of Veterinary Medicine. Following veterinary school, she completed a postdoctoral fellowship at Emory University’s Yerkes National Primate Research Center. Dr. Pendergrass is the founder and owner of JPen Communications, LLC.

References:

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