Summary

A high resolution MRI scanning tool to assist clinicians to evaluate and subsequently improve ACL reconstruction technique, as well as improve surgical planning for revision procedures.

Abstract

Introduction

Positioning of the graft ACL in the native footprint center is important to replicate the anatomy and function of the ACL for each individual patient, as sub-optimal placement is a contributor to poor clinical outcomes postoperatively. Currently, the success of tunnel placement is determined by a combination of diagnostic two-dimensional imaging such as X-ray, MRI or CT, which are time consuming and expensive, lack necessary detail, are largely subjective, and there is no universally accepted quantifiable and objective method to evaluate these imaging studies. High resolution MRI affords the opportunity to evaluate tunnel placement as well as soft tissue characteristics such as cartilage and menisci status or graft integration using a single imaging modality, whilst not imparting radiation to the patient. The goal of this project was to develop a novel MRI-based method for routine assessment of ACL reconstruction, which enables accurate evaluation of femoral and tibial tunnel position as a component of assessing ACLR outcomes, and also to assist in pre-surgical planning for revision reconstruction.

Methods

The study recruited failed primary ACL reconstructed patients (N=25) who had elected to undergo revision ACL reconstruction, to establish the placement of the primary ACL tunnel apertures in the femur and tibia. Prior to surgery each participant underwent high resolution 3T MRI of their injured knee, and 3D models were generated through segmentation of soft and hard tissue knee structures. During surgery previous graft tunnels and prominent reference landmarks visible on MRI and arthroscopically, were registered during the revision procedure using intraoperative navigation to act as the reference standard. Post-surgery the 3D models were aligned to the registered intraoperative landmarks to establish the error between modalities. Using local coordinate systems on the tibia and femur, the position of primary tunnel apertures and graft orientation were quantitatively described relative to the reference landmarks.

Results

The analysis demonstrated that this measurement method can assess the placement of tunnel apertures in the femur and tibia within 0.1 – 1.0 mm of the intraoperative data, using the reference landmarks identifiable in both MRI and arthroscopic assessment. Visual perspective of tunnel placement in three-dimensions identified both gross and subtle tunnel misplacement that may have been misinterpreted from traditional imaging analyses. The combination of accurate measurement and visualisation determined where the graft should be placed in revision surgery relative to anatomical landmarks and the desired graft orientation.

Conclusions

Correct placement of graft ACL bone tunnels inside the native ACL footprint is critical to the outcome of ACL reconstruction. Development of an accurate reproducible method for routine assessment of tunnel placement relative to the anatomical footprint provides an accessible clinical method for objective assessment. The results suggest that graft tunnel placement can be objectively assessed accurately using high resolution MRI scanning, to assist clinicians to evaluate and subsequently improve ACL reconstruction technique, as well as improve surgical planning for revision procedures. Objective measurement of the important variable of tunnel position will also improve the ability to evaluate ACL outcomes in a more meaningful manner.