Abstract
The direction of the force of the quadriceps muscle group is expressed by the value of the quadriceps angle, between the long axis of the muscle rectus femoris and the patellar ligament. This value is often modified in dogs with patellar luxation, a common orthopaedic disease of the stifle joint in both small and large dogs. The aims of the present study were to give a reference value for the quadriceps angle in healthy small and medium-large breed dogs. The medical records of healthy dogs and their pelvic limb radiographs (2014–2016) were reviewed. The radiographs were then divided into two groups: Group A (small dogs <15 kg body weight) and Group B (medium-large dogs >15 kg). The quadriceps angle of each pelvic limb was assessed using a digital software program in order to compare values between the two groups. The radiographs of 160 dogs, 80 per group were studied along with the assessment of the 320 pelvic limbs. The median quadriceps angle values obtained were in contrast with the literature: in Group A, it was 18.3° and, in Group B, it was 8.7°; moreover, the quadriceps angle value for Group A was statistically higher than for Group B (p<0.0001). No significant difference was present between males and females, or between right and left hindlimbs. In Group B, the Labrador Retriever breed influenced the quadriceps angle (p = 0.0005). The outcome of this survey provides an objective parameter, or additional information, to explain the different quadriceps mechanisms of small and medium-large dogs. In future studies the QA range values assessed in the two size groups may be useful in defining the magnitude of the malalignment of the extensor mechanism in both healthy dogs and ones with patellar luxation.
Highlights
Patellar luxation (PL) is a common orthopaedic disease of the stifle joint in both small and large dogs
The findings obtained from the entire sample, from the small and medium-large dogs (QA = 12.4 ̊, 18.3 ̊ and 8.7 ̊, respectively) were in contrast with the quadriceps angle (QA) values found in the literature, referred to as a physiological angle of 10 ̊
In the present study a significant QA difference was found among the two groups (Group A = 18.3 ̊ vs Group B = 8.7 ̊) of normal dogs
Summary
Patellar luxation (PL) is a common orthopaedic disease of the stifle joint in both small and large dogs. Small breed dogs are 12 times more predisposed than large breed dogs to develop medial patellar luxation (MPL) [1]. This statement has been reported in several papers at different times over the last 40 years, i.e. from Trotter [2] and Hayes et al [3] to Hayashi et al [4] and Olimpo et al [5]. The high frequency of MPL in small dogs suggests a hereditary basis and a genetic predisposition [3,6]. The pathogenesis is complex; the patella is part of the extensor mechanism, composed of the quadriceps muscle group, patella, trochlear groove, patellar
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