34th Annual Scientific Meeting proceedings

Objectives:

To propose a failure model applicable to a subset of TPLO cases that can be used for further laboratory analysis and prediction of technique and bone geometry-related risk factors of TPLO failure.

Methods:

Cases with failed fixation of a TPLO procedure were retrieved retrospectively from clinical records. Cases were included if at least a set of orthogonal pre and post-operative radiographic views of the affected limb were available. Radiographs and CT images were assessed for the presence of three failure components: 1. Rock-back, 2. Tibial valgus at the osteotomy site, and 3. Internal rotation of the proximal tibial segment at the osteotomy site. Based on the imaging findings, we hypothesised that the fixations failed after the lateral cortical support collapsed in all cases. To test the hypothesis, we constructed a 3D mechanical model of TPLO failure and conducted mathematical analysis of the tendency of the proximal segment to move relative to the distal one after the bone-implant fixation had failed and the lateral cortical support had collapsed.

Results:

The mathematical analysis concluded that if the lateral cortical support collapses, the resultant deformity at the osteotomy site after the implant-bone fixation has failed would consist of all three failure components tested.

Conclusions:

Rock-back, tibial valgus and internal stifle rotation at the osteotomy site can be the components of TPLO failure after a lateral cortical support collapse. The magnitude of each component and the tendency of failure depend on well-defined parameters. Rock-back could be the sole radiographically detected component of failure in some cases.