Proximal femoral joint orientation line

The proximal femoral joint orientation line is a landmark used to assess angular deformities of the femur and provide guidance for corrections. In particular, it is used to determine and measure the anatomic lateral proximal femoral angle.

In the frontal plane, the proximal femoral joint orientation line is determined from a ventrodorsal radiograph of the hips and femurs or a multiplanar reconstructions of the femur. For radiography, the dog is positioned in dorsal recumbency, pelvic limbs extended caudally, femurs parallel to each other. Positioning is considered satisfactory if :

• the pelvis is symmetrical: the iliums and obturator foramina are symmetrical.

• the femur cortex pass through the middle of the sesamoid bones of the gastrocnemius muscle

• the patellas are centred on the trochlea of the femur.

A best fit circle outlining the head of femur is drawn and it center is determined. The proximal femoral joint orientation line is the line that runs from the center of the femoral head to the dorsal-most aspect of the greater trochanter of the femur.

In the sagittal plane, the proximal femoral joint orientation line is determined from a medio-lateral radiograph of the femur or a multiplanar reconstructions of the femur. For radiography, the positioning is considered satisfactory if the medial condyle and lateral condyle are superimposed.

A best-fit circle is first superimposed over the head of femur and its center is detemined. The portion of the circle (arc) that crosses the femoral neck is redefined as a chord, and the midpoint of this chord is determined. The proximal femoral joint orientation line in the sagittal plane is defined by a straight line connecting the center of the femoral head and the midpoint of the chord.