Evaluation of the radiographic infrapatellar fat pad sign of the contralateral stifle joint as a risk factor for subsequent contralateral cranial cruciate ligament rupture in dogs with unilateral rupture: 96 cases (2006�2007)

• Localización: JAVMA: Journal of the American Veterinary Medical Association, ISSN-e 0003-1488, Vol. 244, Nº. 3, 2014, págs. 328-338
• Idioma: inglés
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• Resumen

  • Objective�To determine prevalence of the contralateral radiographic infrapatellar fat pad sign and contralateral radiographic degenerative sign (degenerative changes) and evaluate both signs as risk factors for subsequent contralateral cranial cruciate ligament (CrCL) rupture in dogs with unilateral CrCL rupture.

    Design�Retrospective cohort study.

    Animals�96 dogs with unilateral CrCL rupture and 22 dogs with bilateral CrCL rupture.

    Procedures�Dogs with unilateral CrCL rupture were classified as having normal (n = 84) or abnormal (12) contralateral stifle joints on the basis of joint palpation. Associations between potential predictive variables and rates of subsequent contralateral CrCL rupture were evaluated.

    Results�Of the 84 dogs with unilateral CrCL rupture in which the contralateral stifle joint was palpably normal, 29 (34.5%) had a contralateral fat pad sign and 31 (36.9%) had a degenerative sign. All dogs with unilateral CrCL rupture in which the contralateral stifle joint was palpably abnormal had a contralateral fat pad sign and degenerative sign. The contralateral fat pad sign was the most important risk factor for subsequent rupture of the contralateral CrCL. For dogs with unilateral CrCL rupture and palpably normal contralateral stifle joint with and without a contralateral fat pad sign, median time to subsequent rupture was 421 and 1,688 days, respectively, and the 3-year probability of subsequent rupture was 85.3% and 24.9%, respectively.

    Conclusions and Clinical Relevance�Bilateral stifle joint radiography should be performed for all dogs with CrCL rupture. Bilateral stifle joint arthroscopy should be considered for dogs with a contralateral fat pad sign.

    Cranial cruciate ligament rupture is a leading cause of lameness in dogs, with a prevalence of 4.9% for dogs evaluated at veterinary medical teaching hospitals in North America.1 Although the epidemiological aspects are diverse, most dogs develop CrCL rupture as a result of progressive pathological ligamentous failure of unknown cause.1,2 Many theories exist, but pelvic limb conformation, in particular deformities of the proximal portion of the tibia leading to an excessive TPA, has garnered much attention as a potential cause of CrCL rupture.3�6 Tibial deformities are assessed partly through measurement of the TPA and the tibial mechanical joint orientation angles.7�11 An important aspect of CrCL rupture is that although many dogs have a history of acute lameness, they often have chronic degenerative changes that are identified on stifle joint radiographs. This suggests that the development of radiographic signs may precede the onset of clinical signs. Another important aspect of CrCL rupture is the high rate of bilateral CrCL rupture, with a lifetime prevalence of 59% to 61%.12,13 Only 4% to 17% of dogs have bilateral CrCL rupture diagnosed on initial evaluation, yet 22% to 54% of dogs with an initial diagnosis of unilateral CrCL rupture will subsequently have contralateral CrCL rupture diagnosed after a median of 10 to 17 months.12�18 As determined on the basis of Kaplan-Meier survival analysis, the median time to subsequent rupture is 947 days, with an exponential decay curve.18 This suggests that subsequent CrCL rupture is diagnosed relatively soon after the initial diagnosis in many dogs.18 The high prevalence of contralateral CrCL rupture subsequent to the initial diagnosis has profound implications for client education, the study of the etiopathogenesis, and the design of potential preventative therapeutics. Several studies12�14,16�19 have investigated potential risk factors to help identify patients at greatest risk for subsequent CrCL rupture. Two early studies14,16 highlighted the importance of bilateral stifle joint radiography in evaluating dogs with unilateral CrCL rupture. Prior to these studies,14,16 the distinction between unilateral and bilateral CrCL rupture was based solely on the clinical signs and orthopedic examination findings, and bilateral radiography was only performed if bilateral CrCL rupture was suspected on the basis of the orthopedic examination findings. In these studies,14,16 50% to 52% of dogs with unilateral CrCL rupture had radiographic findings consistent with CrCL rupture in the contralateral stifle joint. The presence and progression of these findings were both significant risk factors for subsequent contralateral CrCL rupture.14,16 These results suggest that many dogs with diagnosed unilateral CrCL rupture may actually have subclinical bilateral CrCL rupture and that the reported prevalence of bilateral CrCL rupture on initial evaluation may be highly underestimated.14,16,20 One limitation of these studies is that both inflammatory and degenerative radiographic findings of CrCL rupture were grouped together when evaluating potential risk factors for subsequent CrCL rupture.14,16,21 Radiographic effacement of the infrapatellar fat pad shadow is the primary inflammatory finding observed on stifle joint radiographs and has traditionally been termed the infrapatellar fat pad sign.22�24 The fat pad sign is one of the earliest and most consistent findings in dogs with CrCL rupture and is consistent with joint effusion, edema of the fat pad, or periarticular fibrosis.22�24 Radiographic degenerative findings (ie, the degenerative sign) include osteophytosis, enthesiophytosis, and subchondral sclerosis, which signify some degree of chronicity.22�24 Other limitations are that only 49% of the dogs in one study14 had bilateral radiography performed and that the other study16 had a small sample size. It is also unclear how many dogs were excluded from both studies14,16 because of bilateral CrCL rupture.

    Other studies18,19 have since been reported, identifing lymphoplasmacytic synovitis and expression of T-lymphocyte�associated genes as significant risk factors, whereas neutering, a young age at onset, and an increased TPA of the index stifle joint have been inconsistently identified as significant risk factors for subsequent rupture.12,13,17,18 Interestingly, in these studies,12,13,17�19 bilateral radiographs were not routinely obtained and radiographic abnormalities of the contralateral stifle joint were neither assessed nor evaluated as potential risk or confounding factors for subsequent rupture. This suggests that bilateral stifle joint radiography has not yet become a standard of care when evaluating dogs with CrCL rupture.24 It also suggests that unilateral and bilateral CrCL rupture are still being distinguished on the basis of the clinical signs and orthopedic examination findings only.

    The first objective of the study reported here was to retrospectively determine the prevalence of the contralateral fat pad sign and contralateral degenerative sign in a large population of dogs with unilateral CrCL rupture diagnosed on the basis of clinical signs and orthopedic examination findings and for which bilateral radiographs were available. The second objective was to independently evaluate the contralateral fat pad sign and contralateral degenerative sign as potential risk factors for subsequent rupture, controlling for potential confounding variables. The third objective was to evaluate the clinical effect of these risk factors on the pattern of subsequent CrCL rupture by use of regression model survival curves.