Introduction

Cranial cruciate ligament disease (CCLD) is reported to be the most common cause of hind limb lameness in dogs, with the epidemiology and etiology of the disease being frequently studied topics in veterinary orthopedics. The exact pathogenesis of CCLD in dogs remains unclear; however, multiple risk factors, including obesity, abnormal conformation and gait, increased tibial plateau angle, age, and breed, have been implicated with the disease.^1–4 CCLD in cats has not garnered the same robust research initiatives, but it is thought to occur less frequently in the cat population with a similarly unclear pathogenesis.^5–7

Surgical stabilization has long been considered the treatment of choice for dog CCLD. Studies^8,9 have found that only 20% to 30% of dogs weighing greater than 15 kg had improvement in clinical signs with conservative management alone. Those same studies also identified that smaller-breed dogs (weighing < 15 kg) have a better success rate; however, this data has not been updated in over 35 years. Overall, epidemiological studies on CCLD in cats are lacking. Studies have shown that both conservative¹⁰ and surgical intervention, primarily through extracapsular stabilization¹¹ and some osteotomy procedures,^12,13 can be successful in managing CCLD in cats; however, these studies only reported short-term follow-up of 3 to 4 months. A more recent study¹⁴ published in 2020 was the first to describe the characteristics and long-term outcome of both surgically and conservatively treated cats with CCLD in Sweden and Norway. They had a follow-up period of 41 months and found that conservatively treated cats experienced less chronic pain long term than surgically treated cats, suggesting that conservative treatment of CCLD in cats is effective and may be superior to surgical intervention. Given the paucity of literature in this area, the purpose of this study was to describe long-term outcomes of cats managed medically for CCLD via a validated owner-based questionnaire.

Materials and Methods

Medical records of cats that were presented to 2 tertiary referral hospitals between January 1, 2000, and October 1, 2021, were searched to identify records of cats diagnosed with CCLD. Records were reviewed, and history and physical examination findings were recorded, including age, sex, neuter status, breed, onset of lameness, affected limb, body condition score, and comorbidities. Cats were subdivided by body condition score, with underweight being ≤ 2/5 or 3/9; ideal being 3/5, 4/9, or 5/9; overweight being 4/5, 6/9, or 7/9; and obese being 5/5 or ≥ 8/9. The diagnosis of CCLD was based on the presence of cranial drawer sign, cranial tibial thrust, or both during clinical examination. All recommended medical management strategies were recorded. When recommended, strict cage rest was defined as having the cat confined to a large kennel or a small room at all times with no furniture or high surfaces available for jumping.

Follow-up was obtained via phone or email correspondence interview and a 2-part questionnaire from October 11 through 31, 2021. The first part of the questionnaire consisted of 5 multiple-choice questions designed to evaluate short-term (< 6 months) outcomes following initiation of medical management for CCLD, with “normal” being defined as the cat returning to its preinjury level of mobility as assessed by the owner (Supplementary Appendix S1). To assess long-term (> 6 months) outcomes, the validated Feline Musculoskeletal Pain Index—short form (FMPI-sf) metrology instrument was utilized.¹⁵ The FMPI is the most widely studied of the clinical metrology instruments designed to standardize the collection of owner-reported information and has been evaluated for construct validity, internal consistency, reliability, and discriminatory ability in client-owned cats with degenerative joint disease.¹⁵ The FMPI-sf scores were calculated by assigning whole integer scores from 0 to 4, with 0 representing the option of the cat being least affected, and 4 representing the option of the cat being most affected. Total FMPI-sf scores were generated for each cat as mean score per question (maximum score possible was 4). Overall, information gained included whether additional veterinary care related to CCLD was required, assessment of persistent lameness or an approximate timeline for resolution of lameness, perceived outcome without surgical intervention, and the cat’s ability to do everyday activities (jumping, playing, standing up, stretching, grooming). Cats were excluded from the study if there was an uncertain diagnosis, surgical stabilization was performed, or incomplete follow-up information was available.

Results

Eighteen cats were included, with a mean ± SD follow-up time of 66.5 ± 46.7 months (range, 7 to 154 months). Mean ± SD age and body weight of the cats at presentation were 8.8 ± 5.0 years (range, 0.5 to 19.0 years) and 5.8 ± 2.7 kg (range, 2.5 to 15.5 kg). There were 9 spayed females, 8 castrated males, and 1 sexually intact male, with cats reported as domestic shorthair (n = 13), Maine Coon (3), Ragdoll (1), and American Shorthair (1). The left stifle was affected in 8 cats, the right stifle was affected in 8 cats, and 2 cats were affected bilaterally. On the basis of body condition category, 1 cat was underweight, 8 cats had an ideal body condition, 4 cats were overweight, and 2 cats were obese; the remaining 3 cats did not have body condition scores noted in their medical records.

Relevant comorbidities included a capital physeal fracture of the contralateral limb (n = 1), obesity (2), bilateral grade 2/4 medial patella luxations (1), and suspected myelopathy with placing deficits in the pelvic limbs (1). The cat with the capital physeal fracture underwent surgical intervention via a femoral head and neck ostectomy. Nine cats were confirmed to have been alive at the time of follow-up.

Of the 18 cats, 17 were prescribed oral analgesics (Table 1). Additional recommendations included exercise restriction for a mean duration of 6.7 weeks (range, 2 to 8 weeks; n = 14), treatment with polysulfated glycosaminoglycan (Adequan Canine; American Regent Inc; 3), or glucosamine hydrochloride and sodium chondroitin sulfate (Cosequin for Cats [2] or Dasquin for Cats [1]; Nutramax Laboratories Veterinary Sciences Inc) and weight loss (2).

Sixteen of the 18 (89%; 95% CI, 66% to 98%) cats required no additional veterinary care directly related to their CCLD beyond their initial evaluation by the tertiary referral hospital. Of the 2 remaining cats, 1 experienced worsening lameness 2 days after initial presentation and received additional oral analgesia, and 1 received 6 sessions of cold laser therapy with their primary veterinarian. Beyond this, no additional veterinary medical care was reported for any of the cats.

Thirteen of the 18 (72%; 95% CI, 49% to 88%) cats were always able to bear weight or became weight bearing within a week following initiation of medical management. Of the remaining 5 cats, 4 were weight bearing within 2 to 4 weeks, and 1 took > 1 month to become weight bearing. Fifteen of the 18 (83%; 95% CI, 60% to 95%) cats had owner-perceived clinically normal mobility with no observable lameness within 3 months after medical management was initiated, with complete resolution of lameness occurring in < 2 months in 12 of those cats. Of the remaining cats, 1 took > 3 months to become clinically normal, and 2 never became clinically normal. Long term, 17 of 18 (94%; 95% CI, 72% to 100%) owners reported they felt that their cat had a good to excellent outcome with medical management, with the last owner expressing that the outcome was fair.

The mean FMPI-sf ± SD score of all cats was 0.29 ± 0.53 (range, 0 to 2.13). Only 2 cats had FMPI-sf scores > 1 and thus were considered outliers. One of the cats was noted to have remained morbidly obese at the time of long-term follow-up and had an FMPI-sf score of 1.11, whereas the cat with bilateral CCLD coupled with suspected myelopathy had an FMPI-sf score of 2.13.

Discussion

Based on the findings of the present study, cats with CCLD can have excellent long-term outcomes when managed conservatively. The demographics of cats in the present study were consistent with those previously reported, including age, breed, body weight, body condition score, and laterality of the affected stifle.^5,11,14,17 Only one-third of the cats in the present study were classified as overweight or obese. Interestingly, although obesity has been reported to play a role in osteoarthritis development and secondary mobility impairment in both dogs and people, the same causal relationship has not been identified in cats.^18–20 Additional prospective studies of potential risk factors for CCLD in cats are warranted.

Despite variable pain management, activity restriction, and joint supplement treatment, nearly all cats were weight bearing within 1 month. The most commonly utilized orally administered analgesics in the present study were NSAIDs, particularly meloxicam and robenacoxib, which have been documented to be effective for pain control in cats.^21–23 All owners whose cats received NSAIDs reported administering the drugs as prescribed; however, several medical records were lacking information regarding the recommended duration of medication administration. Activity restriction was recommended in the majority of cats, with a minimum of 6 weeks’ restriction being recommended in most cases. It was unknown how strictly the cats were actually confined for the recommended duration of time. Although joint-directed treatment was recommended in several cases, again it was unknown how long cats received joint supplements. The efficacy of joint supplements is difficult to assess, but clinical efficacy of both polysulfated glycosaminoglycan (Adequan; American Regent Inc) and marine-based fatty acids (specifically green-lipped muscles) has been documented in cats.²⁴

Based on the results of the present study, this population of cats had a high overall success rate with medical management alone, with over 90% (17/18 [94%; 95% CI, 72% to 100%]) of cats showing improvement or clinically normal function and nearly all owners feeling that their cats had a good to excellent long-term outcome. This finding is fairly comparable to medical management in small breed dogs, as around 80% of medically managed dogs with CCLD weighing < 15 kg were considered to be clinically normal or improved within 4 to 5 months in 1 study.⁸ The same success has not been documented in larger-breed dogs, and surgery remains the recommendation of choice in those cases.

Overall, the FMPI-sf score for this population of cats was remarkably low, indicating minimal to no evidence of chronic pain. Only 2 cats had FMPI-sf scores > 1, both of which had clinically important comorbidities, with one cat having been morbidly obese and the other having had bilateral CCLD coupled with suspected myelopathy. As the majority of the questions associated with the FMPI-sf were designed to assess mobility, it could have been that both of these cats were more hindered by their comorbidities than by their CCLD. Since cats were not examined by a veterinarian long term, whether they were more hindered by their comorbidities or CCLD remained unknown.

Limitations of this study include its retrospective nature and relatively small number of cases. Importantly, patients were not available for physical examination to assess stability of their stifle joints or for veterinarian evaluation of signs of pain, joint range of motion, or subtle lameness that may be missed by owners. Given that 9 patients were confirmed to have been deceased at the time of surveying and that there was a long duration of follow-up, there was also the potential for a recall bias or difficulties accurately reporting timelines from owners when answering the survey questions. As this was not a prospective study, we could not determine whether patients treated conservatively, versus undergoing surgical repair, take longer to start bearing weight on affected limbs. Additionally, as the cats in the present study did not undergo surgery, the degree of cruciate rupture (ie, partial vs complete) and meniscal status (intact vs torn) was unknown. Although the majority of cats in this study were reported to do well, there may be cases in which surgical intervention is more appropriate to treat cats with CCLD. It was possible that the population of cats in the present study did not have meniscal injury and therefore were able to do well with conservative management, whereas cats that do sustain a concurrent meniscal injury may be better suited for a positive long-term outcome if treated surgically. The consequences of postponing surgical intervention in lieu of medical management in these cases remain unknown. Further studies evaluating the epidemiology of cats with cruciate disease and prospectively assessing long-term outcome of cats treated with surgical stabilization versus conservative treatment are needed to determine what treatment is most ideal for cats with CCLD. Lastly, this was a very small sample size and may not be representative of the larger cat population as a whole. Caution should be taken in interpreting these results when management of cat CCLD is considered.

In conclusion, based on long-term owner follow-up, conservative, nonsurgical management of CCLD can be an effective and appropriate management strategy for cats. However, as we did not compare nonsurgical management to surgical intervention, we cannot say whether one treatment is superior to another. Therefore, when cats are being treated conservatively for CCLD, they should be reevaluated within 2 to 3 months to assess response to treatment, with surgical stabilization being considered if they are not responding well. For cats with severe instability and lameness, surgery may be the best option for treatment at the time of initial diagnosis. Future studies should include prospective assessment of different treatment strategies as well as potential risk factors for development of CCLD in cats to better guide treatment recommendations for CCLD.

Supplementary Material

Supplementary materials are posted online at the journal website: avmajournals.avma.org