Abstract
BackgroundFrench bulldogs exhibit significantly larger femoral external rotation and abduction than other breeds. We were curious as to whether this peculiar leg kinematic affects patellar motion and/or might induce medial patellar subluxation (MPSL) or medial patellar permanent luxation (MPPL). We hypothesized that the more abducted leg posture during stance causes an unusual medial pull direction of the rectus femoris muscle during stance, and that this may facilitate the occurrence of MPSL or even MPPL during locomotion. To test our hypothesis, we analyzed existing stifle-joint X-ray-sequences collected during the treadmill walk and trot of seven adult female French bulldogs. We estimated 3D-patellar kinematics using Scientific Rotoscoping.ResultsThe three-dimensional motion of the patella comprises rotations and translations. From the seven dogs analyzed, three exhibited MPSL and one MPPL during the gait cycle. Medial patellar luxation (MPL) occurred mostly around toe-off in both gaits studied.Patellar position was generally not gait-related at the analyzed timepoints. In dogs with MPL, the patella was placed significantly more distally (p = 0.037) at touch-down (TD) and at midswing (p = 0.024), and significantly more medial at midswing (p = 0.045) compared to dogs without MPL.ConclusionsMedial patellar luxation seems to be the consequence of the far from parasagittal position of the stifle joint during stance due to a broad trunk, and a wide pelvis. This peculiar leg orientation leads to a medial sideway pull caused by the rectus femoris muscle and the quadriceps femoris and may initiate plastic deformation of the growing femur and tibia. Thus, a way to avoid MPL could be to control breeding by selecting dogs with lean bodies and narrow pelvis. Actual breeding control programs based on the orthopedic examination are susceptible to errors. Systematic errors arise from the fact that the grading system is highly dependent on the dog’s condition and the veterinarians’ ability to perform the palpation on the stifle. Based on our results, the position of the patella at TD, or even perhaps during stand might offer a possibility of an objective radioscopic diagnostic of the MPL.
Highlights
French bulldogs exhibit significantly larger femoral external rotation and abduction than other breeds
If one takes the mechanical advantage of the knee into account, which can be described as the fraction between the lever arm of the extensor tendon to the patellar tendon [3], the patella works as an idler gear [4]
We found Medial patellar luxation (MPL) in four of the seven dogs occurring during the gait cycle
Summary
French bulldogs exhibit significantly larger femoral external rotation and abduction than other breeds. It is said that the leverage of the musculus quadriceps femoris is altered and increased, because the torque about the joint depends on the muscle force and the distance to the joint’s center of rotation, so that increased leverage would reduce the necessary muscle force [2]. It is a somewhat more complicated than that. In humans the mechanical advantage of the knee remains mostly lower than 1 during walking and running [5,6,7] This indicates that flexion/extension velocity at the expense of force is being amplified.
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