Evaluation of Trochlear Dysplasia in Dogs with Medial Patellar Luxation - Comparative Studies

Abstract

Background: 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.Materials, Methods & Results: 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 (rho –0.508; 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. Discussion: 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.Keywords: medial patellar luxation, trochlear dysplasia, trochlear depth, small dog breeds.

Computed tomographic measurements of the femoral trochlea in dogs with and without medial patellar luxation

“…We accept our first hypothesis, as in this study the overall FTGA in dogs without MPL was smaller compared to MPL dogs, similarly to what other authors have recently reported. 8,14,15 Among SB and MLB populations, we discovered a mean FTGA of 128 ± 4.7 in SB and 119 ± 5.6 in MLB with cutoff values of 134 and 128 respectively. These data slightly differ from human literature, which suggests that a normal trochlea has an average sulcus angle of 138 ± 6 , while dysplastic trochleae have a sulcus angle >145 .…”

“…[4][5][6] In people, the sulcus angle is usually assessed via radiographic skyline projection. 4,16,30 In veterinary medicine, this projection has been described to evaluate the FTGD, 8,31 but it is not routinely used. In this study, we opted for CT rather than radiographs, since a CT standardized methodology to accurately perform measurements on the femoral trochlear groove has been established.…”

“…Radiographs, 8 ultrasound, 9,10 and computed tomographic (CT) 11–13 examinations were described for measuring the FTGD preoperatively. Radiographs are rarely reported in dogs to evaluate the FTGD, and neither inter‐ and inter‐rater agreement nor accuracy were evaluated 8 …”

“…7 Traditionally, the FTGD has been assessed intraoperatively by subjective visual inspection to evaluate whether the femoral groove requires a trochleoplasty to provide a deeper accommodation for the patella. 1 Radiographs, 8 ultrasound, 9,10 and computed tomographic (CT) [11][12][13] examinations were described for measuring the FTGD preoperatively. Radiographs are rarely reported in dogs to evaluate the FTGD, and neither inter-and interrater agreement nor accuracy were evaluated.…”

“…Radiographs are rarely reported in dogs to evaluate the FTGD, and neither inter-and interrater agreement nor accuracy were evaluated. 8 Ultrasound has shown some benefits for FTGD measurement, as it allows for the simultaneous evaluation of the whole femoral trochlear groove and detection of the cartilage. However, US showed some pitfalls due to the dynamic nature of the examination.…”