Examination of the proximodistal patellar position in small dogs in relation to anatomical features of the distal femur and medial patellar luxation

Abstract

Objective 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). Study design Retrospective case series (n = 71). Methods 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. Results 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. Conclusion 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.

Ideal Anchor Points for Patellar Anti-rotational Sutures for Management of Medial Patellar Luxation in Dogs: A Radiographic Survey

“…23 26 27 28 29 A trend to a more “vertically” oriented trochlea was noted in small breeds with medial patellar luxation. 23 Visually, many of our small breed dogs had “hockey-stick”-shaped distal femora and a relatively large radius to the trochlear arc, resulting in placement of the best-fit centre caudal to the metaphysis. In such cases, placement of a bone anchor relatively distally to ensure appropriate suture tension with the stifle in extension while avoiding excessive tension at other angles might be a solution: if both distal and proximal stabilization is required, a double anchor/suture system may be required, or an alternative means of stabilizing the patella should be employed.…”

“…Limited data are available on femoral condylar morphology, despite morphological studies in medium to large breed dogs, and in small breeds. 23 26 27 28 29 A trend to a more “vertically” oriented trochlea was noted in small breeds with medial patellar luxation. 23 Visually, many of our small breed dogs had “hockey-stick”-shaped distal femora and a relatively large radius to the trochlear arc, resulting in placement of the best-fit centre caudal to the metaphysis.…”

“…A proximally positioned patella (patella alta) is associated with medial patellar instability, since the patella exits the femoral trochlea proximally and loses support from the trochlear ridges, increasing the risk of luxation as the patella moves distally with flexion. 11,20,22,23 Use of a fabellopatellar suture for medial patellar luxation and patella alta should therefore focus on attaining sufficient tension with the stifle joint in extension and the patella in its most exposed position. Our results indicate that this will lead to excessive suture tension at flexed stifle angles.…”

Comparison of patellar position and moment arm between tibial plateau leveling osteotomy and cranial closing wedge ostectomy: An ex vivo study

“…In human medicine, the Insall-Salvati index, which is minimally affected by flexion and extension, is among the most common measurement used in diagnosing patellar alta ( Biedert and Tscholl, 2017 ). Veterinary medicine has applied a similar measurement to the Insall-Salvati index known as the patellar ligament length to patella length ratio (PLL:PL) ( Johnson et al , 2002 , 2006 ; Mostafa et al , 2008 ; Murakami et al , 2021 ). Unfortunately, the PLL:PL cannot directly assess the patellar position relative to the femoral trochlea.…”

“…Therefore, the PLL:PL may be an inappropriate measure for the morphological comparison of the pre-and postoperative patellofemoral joint. In the veterinary field, the proximal and distal patellar positions (PPP and DPP, respectively) are used to evaluate the patellar position relative to the femoral trochlea ( Murakami et al , 2021 ; Johnson et al , 2002 ). However, PPP and DPP are not direct measures of the patellar height as they can be affected by changes in other degrees of freedom of the patella, such as patellar tilt and rotation.…”