Accuracy of fragment positioning after TPLO and effect on biomechanical stability

To compare tibial plateau rotation after tibial plateau leveling osteotomy with the radiographically planned rotation and to determine the effect of translations and rotations of the tibial plateau fragment on the biomechanical stability of the construct under cyclic loading.

Experimental biomechanical study.

Cadaveric canine pelvic limbs (n=10).

Titanium pins were inserted into the tibial plateau and the proximal metaphysis to track the fragment movements by means of computed tomography (CT) imaging. CT scans were performed (1) before osteotomy, (2) after osteotomy and tibial plateau rotation, and (3) after stabilization with plate and screws. The bones were then cyclically loaded in axial compression.

The radiographically planned tibial plateau rotation correlated significantly with the achieved rotation (r=0.73, P=.016), although deviations of up to 4.7 degrees were observed. A significant positive correlation between the amount of rotation about the sawing axis and the plastic deformation of the construct after 30,000 test cycles could be found (r=0.81, P=.005).

Considerable deviation occurred between planned and achieved rotation of the tibial plateau fragment. Lower degrees of rotation were beneficial for biomechanical stability.

Dogs with larger tibial plateau angles may be at a relatively higher risk for fixation failure, but further studies are needed to establish a safe margin of tibial plateau rotation.