Mechanical tibial axis

The mechanical tibial axis is a landmark used to assess angular deformities of the tibia and provide guidance for corrections. It is determined in the frontal and sagittal plane from a radiograph or multiplanar reconstructed CT images of the entire tibia.

In the frontal plane

For radiographic evaluation, the dog is positioned in sternal recumbency, pelvic limbs extended caudally. The caudocranial x-ray beam is centered over the proximal tibia. Positioning is considered satisfactory if :

• the medial and lateral femur corticals passes through the middle of the sesamoid bones of the gastrocnemius muscle.

• the medial aspect of the calcaneus and the intermediate ridge of tibial cochlea are aligned.

The mechanical tibial axis in the frontal plane is the line joining the center of the proximal-most aspect of the intercondylar fossa of the femur and the most distal point of the intermediate ridge of tibial cochlea .

In the sagittal plane

For radiographic evaluation, the dog is positioned in lateral recumbency and a mediolateral radiograph is taken: the view includes the tibia, the stifle joint and the tarsal joint: the beam is centered on the mid-tibial diaphysis with the stifle and tarsus joints both at 90° flexion.

The mechanical tibial axis in the sagittal plane is the line joining the midpoint between the apices of the medial intercondylar tubercule and the lateral intercondylar tubercule proximally, and the center of the head of talus distally.