Evaluation of trochlear dysplasia in dogs with medial patellar luxation: comparative studies

Medial patellar luxation (MPL) is one of the commonest orthopaedic diseases in small dog breeds. Although the bone deformities associated with canine medial patellar luxation are described in numerous studies, the pathogenesis of the condition is still disputable. What is more, there is no categorical evidence that luxation of the patella is associated to a shallow trochlear groove as no objective method for determination of trochlear depth and shape has been proposed. The aim of the present study was to evaluate the depth and shape of femoral trochlear groove on radiographs obtained from healthy dogs and dogs affected with grade II and grade III MPL. A total of 45 dogs (33 with MPL and 12 healthy) from 4 small breeds (Mini-Pinscher, Pomeranian, Chihuahua and Yorkshire terrier) were included in the study. After deep sedation, stifle radiographs were obtained in tangential projection (skyline view). The dogs were positioned in ventral recumbency, the examined stifle bent as much as possible, and the central beam focused on the patella between femoral condyles. Six morphometric parameters associated with the onset of trochlear dysplasia similar to those used in human medicine were measured: trochlear sulcus angle (SA), lateral and medial trochlear inclination angles (LTI; MTI), trochlear groove depth (TD), patellar thickness (PaT) and the ratio between trochlear depth and patellar thickness (PaT/TD). The non-parametric Mann-Whitney test was used for evaluation of differences between healthy joints and those affected with grade II and III MPL. The association between measured variables was evaluated via the Spearman's rank-order correlation. TD was greater in healthy joints as compared to those affected with MPL grade II and III (P < 0.001). In healthy stifles, PaT value exceeded significantly (P < 0.01) that in joints with grade III MPL. The TD/PaT ratio was significantly greater in healthy joints vs both those with grade II (P < 0.01) and grade III MPL (P < 0.001). In healthy joints, there was a significant negative relationship (rho­0.508; P = 0.0113) between SA and TD: smaller sulcus angles corresponded to deeper trochleas. This correlation was even stronger in joints with patellar luxation (rho ­0.723; P < 0.0001). The LTI and MTI showed a very strong positive correlation in healthy joints (rho 0.854; P < 0.0001) and at the same time, lack of significant association in joints affected with MPL (rho -0.163; P = 0.327 for grade II MPL and rho 0.175; P = 0.448 for grade III MPL) was demonstrated. The altered trochlear shape and depth were more pronounced in joints with grade III MPL. As MPL grade increased, the SA became statistically significantly greater. In grade III MPL it was accompanied with considerably reduced trochlear depth, medial trochlear inclination angle and trochlear depth/patellar thickness ratio. Five of the measured morphometric parameters for radiographic detection of trochlear dysplasia in dogs were found to be important in the evaluation of trochlear morphology in dogs. The obtained results indicated the presence of trochlear dysplasia in dogs with MPL. A 3-stage classification system for assessment of abnormal trochlear development in small dog breeds: mild; moderate and severe trochlear dysplasia, was proposed. The occurrence of shallow trochlear groove and medial femoral condyle's hypoplasia could be accepted as signs of mild and moderate trochlear dysplasia. The pre-operative measurements of these parameters could improve surgical planning and decisions-making.

Tratamiento de la inestabilidad femoropatelar objetiva. Resultados a cinco años de seguimiento / Treatment of objective patellar instability. Results after five years of follow-up

Resumen: Objetivo: Presentar los diferentes procedimientos quirúrgicos en el tratamiento de las inestabilidades femoropatelares objetivas, incluyendo la osteotomía de la tuberosidad tibial anterior y la trocleoplastía femoral. Material y métodos: Con un diseño prospectivo con seguimiento a cinco años que incluyó a 21 pacientes (21 rodillas) tratados por luxación rotuliana recidivante entre Marzo de 2010 y Agosto de 2014, tratándose de forma quirúrgica mediante dos técnicas diferentes según el tipo de inestabilidad estructural de base. Para determinarlo, se analizó el índice radiográfico de Caton-Deschamps (para la evaluación de la altura rotuliana) y parámetros tomográficos para valorar el configuración troclear y distancia desde la tuberosidad tibial anterior hasta la tróclea femoral (TT-TG) en la superposición de imágenes en el plano axial. Resultados: Hemos tenido resultados satisfactorios tanto con la transferencia de la tuberosidad tibial anterior como con la trocleoplastía. En ambos procedimientos se realizó una reconstrucción del ligamento patelofemoral medial (LPFM). Conclusiones: La recurrencia de inestabilidad es muy rara después de estos procedimientos y es más probable que ésta resulte de anomalías asociadas no diagnosticadas o subestimadas. Se requiere una planificación precisa preoperatoria para determinar la altura rotuliana, la ubicación de la tuberosidad tibial anterior y la configuración troclear para obtener resultados satisfactorios.

Abstract: Objective: To present the different surgical procedures in the treatment of objective femoropateral instability, including osteotomy of anterior tibial tuberosity and femoral trocleoplasty. Material and methods: With a prospective 5-year follow-up design that included 21 patients (21 knees) treated for relapsing patellar dislocation between March 2010 and August 2014, treated surgically using 2 different techniques depending on the type of basic structural instability. To determine this, the Caton-Deschamps X-Ray Index (for the evaluation of the patellar height) and tomographic parameters were analyzed to assess the troclear configuration and distance from the anterior tibial tuberosity to the femoral trochlea (TT-TG) in the overlapping of images in the axial plane. Results: We have had satisfactory results both with the transfer of the anterior tibial tuberosity and with the trocleoplasty. In both procedures, a reconstruction of the medial patelo-femoral ligament (LPFM) was performed. Conclusion: Recurrence of instability is very rare after these procedures and is more likely to result from undiagnosed or underestimated associated abnormalities. Precise preoperative planning is required to determine the patellar height, location of the anterior tibial tuberosity, and troclear configuration for satisfactory results.