Abstract
To determine the influence of anatomical features of the distal femur on the proximodistal patellar position and compare the proximodistal patellar position between dogs with and without medial patellar luxation (MPL). Retrospective case series (n = 71). Mediolateral-view radiographs of clinical cases of dogs weighing less than 15 kg were obtained. The stifle joint angle, patellar ligament length, patellar length, size of the femoral condyle, trochlear length, and trochlear angle were measured and included in multiple linear regression analyses to ascertain their effects on the proximodistal patellar position. Radiographs were divided into MPL and control groups. The effects of MPL on the proximodistal patellar position and morphological factors were also examined. The final model for the proximodistal patellar position revealed that the patella became distal as the ratio of the patellar ligament length to patellar length decreased, the trochlear angle relative to the femur increased, the trochlear length relative to the patellar length increased, or the trochlear length relative to the femoral condyle width decreased. The proximodistal patellar position in the MPL group was not significantly different from that in the control group despite the trend towards a distally positioned patella (p = 0.073). The MPL group showed a significantly shorter trochlea (p<0.001) and greater trochlear angle relative to the femur (p = 0.029) than the control group. The proximodistal patellar position depends on multiple factors, and its determination based on PLL/PL alone may not be appropriate. Dogs with MPL did not have a proximally positioned patella compared with dogs without MPL. Although hindlimbs with MPL had a shorter trochlea than those without patellar luxation, this difference did not appear to be sufficient to displace the patellar position proximally in small dogs, possibly compensated by increased trochlear angle relative to the femur.
Highlights
The proximodistal patellar position has long been discussed in relation to patellar luxation in dogs [1,2,3,4,5,6,7,8], it is difficult to assess since it changes with stifle flexion or extension [8]
The final model for the proximodistal patellar position revealed that the patella became distal as the ratio of the patellar ligament length to patellar length decreased, the trochlear angle relative to the femur increased, the trochlear length relative to the patellar length increased, or the trochlear length relative to the femoral condyle width decreased
The proximodistal patellar position depends on multiple factors, and its determination based on patellar ligament length (PLL)/patellar length (PL) alone may not be appropriate
Summary
The proximodistal patellar position has long been discussed in relation to patellar luxation in dogs [1,2,3,4,5,6,7,8], it is difficult to assess since it changes with stifle flexion or extension [8]. The ratio of the patellar ligament length to patellar length (PLL/PL) based on the Insall-Salvati index in humans was introduced as an index that is minimally affected by the stifle angle [6, 9,10,11]. One previous study suggested that the long proximal tibia might be the reason for the distally positioned patella of large dogs with lateral patellar luxation instead of a short patellar ligament [5]. No study has evaluated the effect of the anatomical features of the distal femur on the proximodistal patellar position in dogs
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