Abstract
Objectives
The aim of this study was to describe the characteristics and long-term outcome of surgically and conservatively treated cats with cranial cruciate ligament disease (CCLD).
Methods
A retrospective cohort study of cats with CCLD, diagnosed at two university animal hospitals between January 2011 and December 2016, was performed. Signalment, history, treatment and follow-up information were retrieved. Cat owners were contacted for additional long-term follow-up information. The cases were divided into two groups: one conservatively managed and one surgically treated with the lateral fabellotibial suture technique. A quality of life questionnaire, the Feline Musculoskeletal Pain Index (FMPI), was distributed to the owners of cats alive at follow-up for assessment of chronic pain as a long-term outcome. Univariable statistical methods were used to evaluate the data.
Results
Fifty cats were identified and were followed for a median of 41 months after diagnosis of CCLD. Seven cats (14%) developed bilateral CCLD. Twenty-eight cats (56%) were treated conservatively and 22 (44%) surgically. All surgically treated cats in which arthrotomy was performed (19/22) had total cranial cruciate ligament rupture and 9/19 (47%) had meniscal injuries. Postoperative surgical complications were recorded in 6/22 cats (27%). Owners of 24/29 (83%) cats still alive at follow-up completed the FMPI questionnaire. The conservatively treated cats had a lower FMPI score, indicating less chronic pain, than those cats treated surgically (P = 0.017).
Conclusions and relevance
Conservatively treated cats with CCLD experienced less chronic pain at long-term follow-up than surgically treated cats. Bilateral disease is not uncommon in cats with CCLD.
Keywords
Introduction
While cranial cruciate ligament disease (CCLD) in dogs is one of the most discussed and studied topics in veterinary orthopaedics, the condition in cats has gained little attention. Even though the exact aetiopathogenesis of canine CCLD is unknown, multiple risk factors – including breed, sex, age and body weight – have been identified.1–4 The aetiopathogenesis of CCLD in cats is unclear,5,6 and although the disease is reported less frequently in cats than in dogs, 7 epidemiological studies are lacking. In dogs with CCLD, bilateral rupture is reported in approximately 20–50% of cases.8–13 To our knowledge, the occurrence of bilateral disease in cats has not been reported, and the literature is limited to a few cases in case series.6,14 The incidence of meniscal injury in cats with CCLD 14 has been reported to be in the same range as for dogs. 15 Both conservative and different surgical treatments have been deemed successful in feline CCLD.16–18 Extracapsular stabilisation with lateral suture is commonly used, 6 but different osteotomy procedures have been described.17,19
Objective measures of musculoskeletal function in cats can be challenging. Quality of life (QoL) questionnaires provide an opportunity for a standardised assessment of long-term outcome. One such QoL is the Feline Musculoskeletal Pain Index (FMPI), 20 which was designed to assess chronic pain caused by degenerative joint disease in cats. The questionnaire has been validated and undergone reliability testing,20–24 and a Swedish version is available. 25
The objective of this study was to describe the characteristics and long-term outcome of surgically and conservatively treated cats with CCLD. We also aimed to evaluate if treatment method affected the QoL of cats with CCLD.
Materials and methods
Case selection
The medical records of cats with CCLD presented at two university hospitals (University Animal Hospital, Swedish University of Agricultural Sciences; and University Animal Hospital, Norwegian University of Life Sciences) between January 2011 and December 2016 were reviewed retrospectively between 1 March and 1 September 2018. The case population included both referral and primary cases. The diagnosis of CCLD was based on a cranial drawer during clinical examination. Exclusion criteria were an uncertain diagnosis, euthanasia at the time of diagnosis or incomplete follow-up information (eg, where information about whether the cat was alive or not was missing, or the owner could not be contacted).
The records were evaluated for signalment at presentation, including date of birth, breed, sex and body weight. The cats were registered as overweight if they had a body condition score >3.5/5 or >5/9. Neuter status was not registered. History and clinical examination findings were recorded and included onset of lameness, affected limb, time from injury to diagnosis and surgery, contralateral cranial cruciate ligament (CCL) status, insurance status and concurrent orthopaedic diagnosis. Date and cause of death were registered if available. If the cat was diagnosed with bilateral disease during the study period, the characteristics from the first injury was used. For all surgically treated cases, additional information was recorded, including surgeon, date of surgery, arthrotomy, multi-ligament injuries (caudal cruciate ligament [CaCL] rupture, collateral ligament rupture), meniscal injury, antimicrobial therapy, surgical technique and postoperative complications. Owing to the small number of complications, we chose not to classify the complications as major or minor.
Follow-up
Owners and referring veterinarians were contacted by telephone and/or email to obtain additional follow-up information between 1 August and 15 September 2018. Information regarding subsequent contralateral CCLD, additional complications after surgery, date and type of complications, whether the cat was alive or dead, and the date and cause of death was registered. Owners of conservatively treated cats were asked if the cats later had surgery of the affected stifle at other clinics. Follow-up time was calculated as the time from diagnosis to owner contact in the cases where the cat was alive and from diagnosis to euthanasia in the cases where the cat was dead. Cats were presumed to be alive if the information in the medical records was complete and the last registered veterinary visit was in 2018.
Owners of cats that were still alive were asked to complete the FMPI questionnaire in December 2018. The questionnaire contained 18 questions about the cats’ ability to perform different activities, such as running, eating and jumping, and the cats’ overall activity, on a 6 point Likert scale. The results were scored from −1 (above normal ability to perform the activity) to 4 (not at all able to perform the activity), according to Benito et al. 20 The questionnaire also contained two questions about pain in the last week and on the day of assessment, scored from 0 (no pain) to 4 (severe pain), and one question about the overall QoL, scored from 0 (excellent) to 3 (poor) A more detailed description of the questionnaire can be found in the supplementary material, Appendix S1. A low score indicated less chronic pain and a total score of 3 was used as the cut-off value for normal cats. 25 Three additional questions regarding treatment with non-steroid anti-inflammatory drugs (NSAIDs) were included in the questionnaire.
Statistical analysis
Data were compiled in Microsoft Excel and imported into Stata 15, which was used for all statistical analyses. A P value of <0.05 was considered statistically significant. Normality was assessed graphically for continuous variables and is presented as median (range). Categorical variables were described as percentages. Association between categorical and continuous variables were explored by the two-sample t-test and Wilcoxon rank sum test for normally and non-normally distributed variables, respectively. Associations between categorical variables were tested using the χ2 test or Fisher’s exact test. A multivariable analysis was not performed owing to the homogeneity of the material and lack of statistical power because of the limited number of cases.
Results
Case inclusion
During the 6 year period, 60/493 (12.2%) of the patients diagnosed with CCLD were feline, of which 50 had complete follow-up information and were included in this study. Sex distribution was even. Median age at time of diagnosis was 9.0 years. Median weight was 4.9 kg and 20 cats were registered as overweight. Thirty-seven cats were insured (see Table 1). Seven breeds were represented. Thirty-nine cats (78.0%) were mixed breed (domestic shorthair and domestic longhair). The remaining cats included three British Shorthairs, two Maine Coons, two Norwegian Forest Cats and two Siberians, one European Shorthair and one Persian.
Descriptive features of 50 cats with cranial cruciate ligament disease presented at two university animal hospitals
Continuous variables reported as median (range) and categorical variables as n (%)
P = 0.03. These were the only variables where a statistically significant difference was detected between the groups
Missing value from one surgically treated cat, n = 49
SLU = Swedish University of Agricultural Sciences; NMBU = Norwegian University of Life Sciences; QoL = quality of life questionnaire
The left CCL was injured in 28 cats, and the right in 22. The most common clinical presentation was acute onset of lameness with duration <1 week prior to diagnosis (Table 1). Two cases of concurrent medial patellar luxation (MPL) and one case of femoral fracture were diagnosed. Both cats with MPL were conservatively treated, while the femoral fracture was treated surgically with a femoral head and neck resection during the same procedure.
Treatment
Of the 50 cats, 28 were treated conservatively and 22 received surgical treatment. None of the initially conservatively treated cats needed surgical intervention later. The time from injury to diagnosis was shorter for the conservatively compared with the surgically treated cats (P = 0.03) and conservative treatment was chosen more often at the Swedish University of Agricultural Sciences than at the Norwegian University of Life Sciences (P = 0.03). None of the other variables included were significantly different between the groups (Table 1).
Twelve surgeons with different levels of experience performed the procedures; the lateral fabellotibial suture (LFS) technique was used in all cats. Arthrotomy was performed in 19/22 surgeries and a complete CCL rupture was noted in all. Multi-ligament stifle injuries were diagnosed in five surgically treated cats; four had collateral ligament damage and two of these had an additional complete rupture of the CaCL. The fifth cat had CaCL rupture but intact collateral ligaments. Meniscal injury was noted in nine cats. However, information regarding treatment of the meniscal injuries, and the extent and type of meniscal damage was inconsistent in the records and was therefore not included. Further details for the surgically treated cats are given in Table 2.
Data from 22 surgically treated cats with cranial cruciate ligament disease presented at two university animal hospitals
Percentage of cats with arthrotomy performed
CaCL = caudal cruciate ligament
Complications and follow-up
Postoperative complications were recorded in 6/22 (27.3%) surgically treated cats. There was no statistical difference in complication frequency between the two clinics (P = 0.35), or between the cases with multi-ligament stifle injuries and those without (P = 0.59). Two cats had one postoperative complication, while four cats had two. Three of the six cats with complications underwent a second surgery (Table 3).
Details for the six surgically treated cases with postoperative complications in a retrospective study of 50 cats with cranial cruciate ligament disease
CaCL = caudal cruciate ligament; FMPI = Feline Musculoskeletal Pain Index; NSAIDs = non-steroidal anti-inflammatory drugs; OA = osteoarthritis; NA = not applicable; ROM = range of motion; FeLV = feline leukaemia virus
Eighteen of the surgically treated cases received perioperative antibiotic treatment. Seven of these were also administered antibiotic treatment postoperatively. One of these cats had a wound injury, while no justification for antibiotic use was given in the others.
Two conservatively and five surgically treated cats developed bilateral disease (14.0%). The median interval between the bilateral injuries was 18.8 months. There was no difference in either median weight or percentage of overweight cats among the cats with bilateral disease vs cats with unilateral disease (5.1 kg and 42.9% vs 4.9 kg and 39.5%, respectively). The number of bilateral cases was not statistically different between the conservatively and surgically treated cats (P = 0.12).
The median follow-up time for the 50 cats was 41.1 months (Table 1). Twenty-nine were alive and 21 were dead at follow-up.
QoL questionnaire
The FMPI questionnaire was completed by 24/29 (82.8%) of the cat owners with a median total score of 3 (range −6 to 15). The FMPI was answered by the owners of 2/5 cats with multi-ligament injuries. These two cats had a median total score of 13 (range 11−15) vs 4 (range 0–15) in the 10 surgically treated cats without multi-ligament injuries. The median total score of all the surgically treated cats was 5 (range 0−15) vs 0.5 (range −6 to 7) in the conservatively treated cats (P = 0.02).
When the two cats with multi-ligament injuries were excluded, the difference between the groups was still significant (P = 0.05). Three of 12 conservatively treated and 8/12 surgically treated cats had a total score >3, with the difference in proportions being statistically significant (P = 0.04). None of the cats received NSAID treatment at the time of follow-up. Further results are given in Table 4, and the FMPI scores from the cats with postoperative complications in Table 3.
Comparison of Feline Musculoskeletal Pain Index (FMPI) results at long-term follow-up between conservatively and surgically treated cats with cranial cruciate ligament disease
Results from 18 activity questions (scored −1 [above normal activity] to 4 [no activity at all]), two pain questions (scored 0 [no pain] to 4 [severe pain]) and one quality of life (QoL) question (scored 0 [excellent] to 3 [poor]). A low total score indicated less chronic pain.
P values from Wilcoxon signed rank test
NA = not analysed owing to high number of zero values
Discussion
CCLD is considered an uncommon disease in cats. Even though several sources state that CCLD is less common in cats than in dogs,7,26,27 this is the first time a comparison has been published. The low percentage (12.2%) of feline patients with CCLD in our study supports the previous assumption that CCLD is more common in dogs than in cats.
The age of the cats in our study is comparable to earlier reports,6,14,17 and the weight is similar to that of randomly selected healthy controls in two earlier studies of CCLD in cats.5,6 A greater proportion of cats in our study was insured vs the general insurance coverage (35.7% in 2012) of cats in Sweden. 28 This discrepancy in insurance coverage could indicate that owners of insured cats are more likely to seek veterinary advice in cases of CCLD. This is in agreement with Taylor-Brown et al, 3 who reported that insured dogs had four times higher odds of a CCLD diagnosis than uninsured dogs. As the number of insured cats in our study was approximately equal in the two treatment groups (Table 1), we can assume that insurance status did not influence the choice of treatment.
The incidence (47%) of meniscal injury in surgically treated cats in our study was somewhat lower than an earlier report of 67% meniscal injuries in cats surgically treated for CCLD, 14 but in the same range as the percentage of meniscal injuries reported in canine studies.15,29 It should also be noted that another study with a limited number of cats identified meniscal tears in only 2/11 cats. 17
None of the surgically treated cats in the current study had partial CCL ruptures. This is in agreement with an earlier study in cats, 14 but is in contrast to the higher proportion of partial CCL ruptures in dogs. 15 As the degree of rupture was unknown in the conservatively managed cats, it is possible that this group had a higher percentage of partial ruptures than the cats treated with surgery. Other studies have suggested that partial ruptures can be clinically silent and thus not detected by the owners.14,17 If a partial rupture produces only mild or no clinical signs, it is likely that the actual proportion of partial CCL rupture in cats is higher than reported in this study. To address this question, a post-mortem examination of a larger number of cats would have to be performed.
A degenerative process in the ruptured CCL has been reported in dogs,30,31 and there is an ongoing discussion about the aetiology of CCLD in cats.5,6 A recent study by Wessely et al 5 found no histological evidence of a degenerative process in the CCL of cats, while a study by Harasen 6 supported both a traumatic and a degenerative aetiology of the disease. However, only a single CCL was examined histologically in the latter study.
The percentage of cats with bilateral disease in our study was substantially lower than the 20–50% typically reported in canine studies,8–13 despite a long follow-up. In addition, several of the cats had CaCL ruptures and collateral ligament injuries, which is rare in dogs with CCLD.32,33 Together, this could support a degenerative aetiology in dogs and a traumatic aetiology in cats. However, with CCLD being an uncommon disease in cats, 14% of bilateral disease is a substantial number if the aetiology is solely traumatic. We emphasise the need for prospective studies of potential risk factors for CCLD in cats, preferably with a larger number of cases, including histological examinations of the ruptured ligaments.
Postoperative complications were relatively common in our study. Even though the reason for this is unknown, several surgeons with different levels of experience performed the procedures and we cannot exclude the possibility that the low number of LFS surgeries per surgeon contributed to the complication risk.
The results from the QoL investigation showed that a substantial proportion of the cats had a FMPI score indicative of chronic pain. However, none of the cats received NSAID treatment at follow-up. Moreover, most of the owners with cats scoring high on the FMPI did not perceive their cat as being painful. This implies that signs of chronic pain in cats can be subtle and may go unnoticed by the owners.
This is the first epidemiological study of CCLD in cats including both surgically and conservatively treated cats. A higher proportion of the surgically than the conservatively treated cats had an FMPI score >3, indicating chronic pain. It is perhaps not surprising that all the cats with postoperative complications had high scores.
Previous studies have reported a normal locomotion pattern 1 year after experimental CCL transection in cats, 34 and good functional recovery after conservative treatment of CCLD. 16 This is in contrast to the study by Ruthrauff et al, 14 which suggested that surgical stabilisation with stifle exploration should be considered in cases of feline CCLD due to the progression of degenerative joint disease as a result of meniscal injury. As mentioned, meniscal injuries were common among the surgically treated cats in our study. Nevertheless, the FMPI scores indicated that chronic pain was more common in the surgically treated than in the conservatively treated cats. Even though the degree of meniscal injury was unknown in the conservatively treated cats, these findings do not support meniscal injury as an argument for surgical treatment is cases of feline CCLD.
In cats where multi-ligament injuries result in a severely unstable stifle joint, surgical stabilisation is recommended. 35 The FMPI results of the cats with multi-ligament injuries in the current study show that chronic pain could be expected in these cats, even after surgical correction. However, even after excluding these cats, the median FMPI scores were significantly higher for the surgically treated than the conservatively treated cats.
Cats treated conservatively were not evaluated by arthrotomy, and information about partial or full CCL rupture or meniscal injury is therefore not available. A possible selection bias due to a clinical decision to treat less lame cats with less severe joint disease conservatively cannot be excluded. It is unknown whether this has affected the long-term FMPI score.
Surgical procedures are always associated with some degree of stress and pain for the animal, in addition to substantial costs for the owner. From this perspective, the current findings support conservative treatment in cases of isolated CCLD in cats. However, one should refrain from drawing definite conclusions owing to the risk of bias, the small number of cats and the lack of a clinical assessment of long-term function in our study.
Our study has several important limitations. The retrospective study design introduces several potential sources of bias, such as recall bias and misclassification errors. Another limitation is the unbalanced number of cats at the two clinics and the relatively small number of cases. In addition, information regarding the severity of lameness at initial presentation was not available and it is possible that the degree of lameness affected treatment choice and consequently the FMPI scores. Even though the response rate to the FMPI questionnaire was high, there is a risk of non-responder bias. Moreover, the cats in our study may not reflect the general population as both clinics are referral hospitals. Even though cats with osteoarthritis often do not show signs of overt lameness, 36 the absence of osteoarthritis grading in the cats in our study is another limitation. The degree of osteoarthritis in relation to treatment and long-term outcome in cats with CCLD should be addressed in the future.
Conclusions
In the present study, conservatively treated cats with CCLD experienced less chronic pain at long-term follow-up compared with surgically treated cats, according to a QoL assessment. Multi-ligament stifle injuries, meniscal disease and postoperative complications were frequently observed in surgically treated cats. Subsequent CCLD in the contralateral stifle occurred in 14% of the cats. Prospective studies with an objective assessment of different treatment strategies and risk factors for bilateral CCLD are warranted.
Supplemental Material
Appendix S1
Shortened English version of the quality of life questionnaire with descriptive rating scale. The data that support the findings of this study are available from the corresponding author upon reasonable request
Footnotes
Acknowledgements
The authors would like to acknowledge the assistance of Professor Ulf Emanuelson and Professor Eystein Skjerve in the preparation of this manuscript and for advising on the statistical analysis, and Caroline Mason for help in collecting data.
Supplementary material
The following files are available: Appendix S1: Shortened English version of the quality of life questionnaire with descriptive rating scale. The data that support the findings of this study are available from the corresponding author upon reasonable request.
Conflict of interest
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The PhD project of one of the authors (KE) is financed by Agria Pet Insurance Research Foundation. No other financial support for the research, authorship, and/or publication of this article was received.
References
Supplementary Material
Please find the following supplemental material available below.
For Open Access articles published under a Creative Commons License, all supplemental material carries the same license as the article it is associated with.
For non-Open Access articles published, all supplemental material carries a non-exclusive license, and permission requests for re-use of supplemental material or any part of supplemental material shall be sent directly to the copyright owner as specified in the copyright notice associated with the article.
