Problem
ACL revision surgery evaluation to determine the possibility of one-stage repair or the need for two-stage repair, based on computer-aided planning and 3D open source software.

Background

CT or MRI images alone provide information about tunnel length and diameter, but the spatial orientation of the resulting graft direction and relations must be 'imagined' by the surgeon, relying on its expertise.

Objective

We propose a workflow that allows direct visual graft and tunnel positioning. We can preoperatively evaluate future tunnels entry point, superposition, graft direction, and bony defects. This pre op plan allows us to determine whether a revision surgery may need a previous procedure for bony defect filling or its suitable for one-stage graft revision.

Hypothesis

3D planning and guided surgery are currently accepted practices that have demonstrated its added value surpasses the direct cost of their implementation.
In cases of ACL primary surgery failure, the position of the tunnels, their trajectory, entry points and diameter are of crucial importance. The surgical procedure will not be equal in cases with properly oriented small diameter tunnels, as when large bony defects requiring first stage bone grafting are found. In the same scenario, major defects can be avoided if the orientation of the revision tunnel does not overlap the path of the initial tunnel. In case of malposition of previous tunnels, it allows addressing if the proposed location would prevent a new failure, tunnel overlap or graft impingement during the knee ROM.

Methods

We use open source software for all the stages of the procedure.
The DICOM images from the CT are processed with Slicer3D to obtain the mesh model after segmentation. We use either the Threshold or the Grow from seeds method for segmentation. Tunnels and graft trajectory simulation with Blender.
We evaluated the trajectory of the failed ACL at different points of the mobile arc of the joint, the diameter and path of the initial tunnels. We then simulated the trajectory and diameter of future tunnels and verified the positioning of the future graft at different angles of the flexion. We are currently working on the development of a surgical guide adapted to the anatomy of each particular case for guiding the tibial and femoral tunnels.

Results

Our Computer-assisted 3D workflow allows us to plan a surgery, avoiding unexpected situations and overcoming possible inaccuracies occurred at the time of the primary procedure. Relying on the diameter, direction and bony defects measured during the planification, we plan a single or staged surgery.

Conclusion

We have applied for the first time computer-aided 3D design technology to arthroscopic knee surgery to plan ACL graft revisions with a reproducible result. This method is a fundamental tool for designing specific instruments for ACL surgery, allowing to save time and effort in the less standardized steps of the procedure such as tunnel positioning.