How to plan a MCCWO modified cranial closing wedge ostectomy in VPOP PRO eTPA series

Welcome to another VPOP Pro tutorial! This is the first in a series of ETPA levelling videos. Today, we’ll cover two precise planning options for achieving a five-degree post-op TPA consistently using a modified cranial closing wedge ostectomy technique. We will demonstrate how to set your target TPA to 5 degrees and utilize the reposition tool and wedge tool to create a reproducible, intuitive plan that can be executed in the OR.

Introduction

Thanks to Frederick and Cross’s paper in 2016 and special thanks to Dr. Cross for allowing direct references, we know that a modified wedge technique can level those stifles with ETPA. The approach involves taking an asymmetric wedge to level the ETPA while minimizing the loss in tibial length associated with wedge techniques.

Setting the Target TPA

1. Defining the Mechanical Axis:
   • On the left image, we have a proximal target mechanical axis based on a target post-op TPA of 5 degrees, intersecting with the blue existing mechanical axis.
   • The existing mechanical axis is defined by landmarks proximally at the intercondylar eminences and distally through the centre of the talus.
2. Planning the Osteotomy:
   • On the right image, to achieve this, we take out an asymmetric wedge and define the proximal fragment to reduce.
   • This involves an initial cranial long-axis shift followed by a caudal long-axis shift, optimizing cortical alignment.

Detailed Planning Steps

Step 1: Defining the Osteotomy

1. Define the transverse osteotomy level at the distal end of the tibial tuberosity.
2. Realign the proximal fragment with the target mechanical axis, passing through the centre of the talus.

Step 2: Using the Wedge Tool

1. Identify the surplus bone that needs to be removed.
2. Select the wedge tool from the top right menu.
3. Place the wedge over the area of bone to be removed. In this case, it’s a wedge of 49.9 degrees.

Step 3: Measurement and Annotation

1. Measure and annotate using the tools provided.
2. Measure distances (D1, D2, D3) from known landmarks in surgery.
3. Use the annotation tool to document these measurements.

Step 4: Selecting an Implant

1. Go to the implant menu and choose the appropriate implant from various manufacturers.
2. Adjust the implant size and orientation to ensure robust fixation for the patient.

Detailed Walkthrough

Using the Reposition Tool

1. Defining the Wedge:
   • Use the annotations tool to define the distal component of your wedge, starting at the distal extremity of the tibial crest.
2. Setting the Target Lines:
   • Use the line tool to create two lines: one for the long axis from the distal landmark (centre of the talus) and another 5 degrees off perpendicular.
3. Reposition Tool Application:
   • Select the reposition tool and align the osteotomy fragments. Adjust cranial and caudal alignment to achieve the target 5-degree TPA.
4. Final Adjustments:
   • Make precise adjustments using the axis and angle tools until the 5-degree target is met.

Using the Wedge Tool

1. Defining and Placing the Wedge:
   • Place the wedge over the surplus bone stock, ensuring the green hypotenuse aligns with the proximal end.
2. Repositioning the Wedge:
   • Reposition the wedge to match the transverse osteotomy, ensuring the base height and angle are correct.
3. Measuring and Annotating:
   • Measure the wedge position from known landmarks and annotate these measurements.

Starter Wedge Method

1. Setting Initial Axes:
   • Define proximal and distal axes and apply the cora magnitude to a wedge.
2. Adjusting the Wedge:
   • Track the long-axis shift and adjust the wedge as needed to achieve the 5-degree TPA.
3. Final Measurement and Annotation:
   • Measure and document the wedge’s position, ensuring precise planning for surgery.

Conclusion

By the end of this tutorial, you should be able to plan precisely for a 5-degree TPA using either the superimposition method or the starter wedge method in VPOP Pro. This plan will guide you through a modified cranial closing wedge ostectomy with confidence and accuracy.

Special thanks to Dr. Scott Featherston for supplying the radiographs used in this video tutorial.

This concludes the tutorial on ETPA levelling with VPOP Pro. Thank you for following along, and stay tuned for more detailed planning and surgical techniques in our upcoming videos!