Table 1. Radiographic measurements of the stifle and tibia used to derive principal components and phenotypes for genome wide association study.

Lateral projection	Radiographic measurement
Tibial plateau angle	One line connecting the center of the talus to the center of the tibial intercondylar eminences. A second line along the tibial condyles connecting the point just caudal the insertion of the cranial cruciate ligament and extending caudally to pass through the caudal tibial plateau as it deviated distally to join the proximal tibial metaphysis. The obtuse angle between these two intersecting lines was the TPA.
Tibia length	A line originating at the center-point of the lateral malleolus of the fibula and ending at the proximal intercondylar eminence.
Tibial diaphyseal width	The distance between the outside cortices at the mid tibial diaphysis
Tibial tuberosity length	A line connecting the proximal and distal tibial tuberosity
Infrapatellar fat pad height	The distance at the caudal edge of the patellar ligament from the distal patella to its insertion on the tibial tuberosity
Infrapatellar fat pad width	At its widest point, a line perpendicular to the height of the infrapatellar fat pad caudal to the edge of the soft tissue opacity within the joint space
Cranial Caudal Projection
Tibial diaphyseal width	At the mid-point of the tibial diaphysis, the width to each outer cortex
Femoral condyle width	A line perpendicular to the long axis of the femur at the level of the base of the intercondylar fossa, extending from the medial to the lateral femoral condyles
Femoral notch width	A line perpendicular to the long axis of the femur at the mid-point of the intercondylar fossa and extending between the axial borders of the femoral condyles
Tibial plateau width	A line perpendicular to the long axis of the tibia at the proximal aspect of the tibial metaphysis